[Feat] (MG_State, MG_Util): async shader compilation behind the default-off flag (P1 stage 3)

glCompileShader with MOBILEGL_ASYNC_SHADER_COMPILE=1 snapshots its inputs on
the GL thread (source SharedPtr, CompileEnv, cache handle) and runs the whole
pure pipeline - preprocess, validators, extractors, glslang parse - as a
ShaderCompileTask on the worker pool, returning immediately. Every read of
compile-produced state joins through the single Compiled() gate; links stay
synchronous this stage and join their attached shaders at the top of the
body. Flag off, the path is the same code run inline.

Mechanics: the job node owns all its inputs (no back-pointer, no lifetime
tie to the shader object), so re-sourcing or deleting a pending shader is
cancel-and-drop, never a wait; glslang worker hygiene is a TLS-allocator
scope guard plus GL-thread builtin prewarm (gated on the flag, latch reset
on Destroy so re-initialization re-warms); worker-side diagnostics defer
through the job and replay on the GL thread at the join, enforced by
IsPoolThread asserts in RecordError and an empty-deferred-errors tripwire.
A body that throws publishes a COMPLETE failed compile (status false, real
info log) rather than an abandoned node, and never memoizes away the retry;
a failed enqueue (OOM) cancels the node instead of stranding the joiner -
including inside the dispatch loop, where the in-flight slot is repaid.
The pool StopAndDrains from an atexit sentinel too: workers still inside
glslang parse while exit() ran static destructors was a real 2-in-5 SIGSEGV,
reproduced and fixed (15/15 clean after).

Backend-internal shader objects (default FS, DirectVulkan blit/mipmap) are
cache-less and always compile inline - compile-and-read-in-one-breath needs
no round trip.

Gates: unit suite 488/488 with the flag off AND on (x5); AsyncCompileTest
(12 e2e cases: pending re-source/delete/recompile, byte-identical failure
logs across modes, 48-compile cache stress) x10 repeats clean both modes;
full NVIDIA DirectGLES retrace identical result sets flag off/on (zero new
deltas); compile-phase timing flat as designed (links still serial - the
parallel win arrives with stage 4's async link + stage 5's
KHR_parallel_shader_compile).

CMakeLists.txt

@@ -294,6 +294,7 @@ set(SOURCE_FILES
     MobileGL/MG_State/GLState/TextureState/TextureUnit.cpp
     MobileGL/MG_State/GLState/TextureState/TextureState.cpp
     MobileGL/MG_State/GLState/ProgramState/ProgramObject.cpp
+    MobileGL/MG_State/GLState/ProgramState/ShaderCompileTask.cpp
     MobileGL/MG_State/GLState/ProgramState/ShaderObject.cpp
     MobileGL/MG_State/GLState/ProgramState/ShaderPreprocessCache.cpp
     MobileGL/MG_State/GLState/ProgramState/ProgramState.cpp

MobileGL/Init.cpp

@@ -16,6 +16,7 @@
 #include <MG_Impl/GLImpl/Framebuffer/GL_Framebuffer.h>
 #include <MG_Impl/GLImpl/Sync/GL_Sync.h>
 #include <MG_Util/Async/ShaderCompilePool.h>
+#include <MG_Util/ShaderTranspiler/ShaderCompiler.h>
 
 #include <atomic>
 #include <mutex>
@@ -61,6 +62,10 @@ namespace MobileGL {
             // still reference levels adopted from those tables. Finalizing first left live
             // glslang objects pointing at freed memory for the rest of the teardown.
             glslang::FinalizeProcess();
+            // Immediately after, and never apart from it: FinalizeProcess just deleted the
+            // built-in symbol tables the prewarm latch stands for, so leaving it set would
+            // make the next Initialize() skip a prewarm it genuinely needs.
+            MG_Util::ShaderTranspiler::ShaderCompiler::ResetPrewarmLatch();
             MG_Backend::gBackendFunctionsTable = {};
             g_isInitialized = false;
             if (logLifecycle) {
@@ -88,6 +93,19 @@ namespace MobileGL {
         MG_Impl::Init();
         MGLOG_D("MG_Impl initialized");
         glslang::InitializeProcess();
+        // On the GL thread, before any worker can exist. glslang builds its built-in symbol
+        // tables lazily under a process-wide lock held for the whole build, so without this
+        // the first concurrent compiles of a shaderpack all serialize behind the very first
+        // parse and asynchronous compilation looks like it is doing nothing.
+        //
+        // Gated on the flag, because the problem it solves only exists when there are
+        // workers: with compilation synchronous, nothing ever contends for that lock and the
+        // three throwaway parses buy nothing - they just add to every eglInitialize. Read the
+        // flag here rather than inside PrewarmBuiltins so ShaderCompiler keeps no dependency
+        // on the async subsystem (ProgramUtilTest compiles that file without it).
+        if (MG_Util::Async::AsyncShaderCompileEnabled()) {
+            MG_Util::ShaderTranspiler::ShaderCompiler::PrewarmBuiltins();
+        }
         MGLOG_D("glslang initialized");
         g_isInitialized = true;
         MGLOG_I("MobileGL initialized");

MobileGL/MG_State/GLState/Core.cpp

@@ -10,6 +10,7 @@
 #include "MG_State/GLState/RenderbufferState/RenderbufferObject.h"
 #include "MG_State/EGLState/Core.h"
 #include <MG_Backend/BackendObjects.h>
+#include <MG_Util/Async/ShaderCompilePool.h>
 #include <MG_Util/ShaderTranspiler/CompileEnv.h>
 #include <Config.h>
 
@@ -40,6 +41,13 @@ namespace MobileGL::MG_State {
 
         // Error
         void GLContext::RecordError(ErrorCode code, UniquePtr<ErrorInfo> info) {
+            // Invariant I1, mechanically enforced: the GL error state is GL-thread-owned.
+            // A compile or link body that needs to raise an error must append to its node's
+            // JobDiagnostics and let the join replay it here (see the P1 design section 6);
+            // reaching this from a worker would corrupt the sticky-flag set that
+            // glGetError's ordering depends on.
+            MOBILEGL_ASSERT(!MG_Util::Async::ShaderCompilePool::IsPoolThread(),
+                            "GLContext::RecordError() called from a shader-compile pool thread");
             m_errorState.RecordError(code, Move(info));
         }
 

MobileGL/MG_State/GLState/ProgramState/ProgramObject.cpp

@@ -572,6 +572,20 @@ namespace MobileGL::MG_State::GLState {
         // below is a pure function of the snapshot taken here, which is what lets stage 4
         // lift it into a ProgramLinkTask. `env` is the first piece of that snapshot: the
         // link's only window onto the backend.
+
+        // P1 stage 3: linking is still synchronous, so every attached shader's compile has
+        // to be settled before the body below touches a single one of its artifacts. One
+        // loop up front rather than leaning on the per-accessor gate, deliberately: it lets
+        // all the outstanding compiles finish concurrently and blocks once at the end,
+        // instead of serializing them one join at a time down the loop below.
+        //
+        // Placed AFTER the prologue, not before it, so it joins exactly the shader set this
+        // link will read. Shaders removed by the detach pass above are not joined - the link
+        // never reads them, their objects are still alive, and whoever queries one next
+        // joins it then.
+        for (const auto& shader : m_shaders) {
+            shader->JoinCompile();
+        }
         const SharedPtr<const MG_Util::ShaderTranspiler::CompileEnv> envPtr =
             MG_Util::ShaderTranspiler::GetCurrentCompileEnv();
         const MG_Util::ShaderTranspiler::CompileEnv& env = *envPtr;

MobileGL/MG_State/GLState/ProgramState/ProgramState.cpp

@@ -120,6 +120,11 @@ namespace MobileGL::MG_State::GLState {
         auto& shaderObject = m_shaderObjects[shader];
         if (shaderObject == nullptr || !shaderObject->GetDeleteStatus()) return;
         if (ShaderHasGLVisibleAttachment(shaderObject)) return;
+        // The name is about to go: nothing can observe this shader's compile any more, so a
+        // job still in flight for it is pure waste. Cancel-not-join - the job owns its
+        // inputs, so dropping the object out from under it is safe and the GL thread never
+        // blocks on a delete.
+        shaderObject->CancelCompile();
         shaderObject.reset();
         m_programShaderNameGenerator.Delete(shader);
     }

MobileGL/MG_State/GLState/ProgramState/ShaderCompileTask.cpp

@@ -0,0 +1,303 @@
+// MobileGL - MobileGL/MG_State/GLState/ProgramState/ShaderCompileTask.cpp
+// Copyright (c) 2025-2026 MobileGL-Dev
+// Licensed under the GNU Lesser General Public License v3.0:
+//   https://www.gnu.org/licenses/gpl-3.0.txt
+//   https://www.gnu.org/licenses/lgpl-3.0.txt
+// SPDX-License-Identifier: LGPL-3.0-only
+// End of Source File Header
+
+#include "ShaderCompileTask.h"
+
+#include <MG_Util/Converters/MGToGL/ProgramEnumConverter.h>
+#include <MG_Util/ShaderTranspiler/ShaderCompiler.h>
+#include <MG_Util/ShaderTranspiler/ShaderSourceProcessor.h>
+#include <MG_Util/ShaderTranspiler/Types.h>
+
+#include <glslang/Include/PoolAlloc.h>
+
+#include <charconv>
+
+namespace {
+    struct ComputeLocalSize {
+        MobileGL::Uint x = 1;
+        MobileGL::Uint y = 1;
+        MobileGL::Uint z = 1;
+        bool declared = false;
+    };
+
+    static MobileGL::String StripGlslComments(const MobileGL::String& source) {
+        MobileGL::String result;
+        result.reserve(source.length());
+
+        bool inLineComment = false;
+        bool inBlockComment = false;
+        for (MobileGL::SizeT i = 0; i < source.length(); ++i) {
+            if (inLineComment) {
+                if (source[i] == '\n') {
+                    inLineComment = false;
+                    result.push_back(source[i]);
+                } else {
+                    result.push_back(' ');
+                }
+                continue;
+            }
+
+            if (inBlockComment) {
+                if (source[i] == '*' && i + 1 < source.length() && source[i + 1] == '/') {
+                    inBlockComment = false;
+                    result.append("  ");
+                    ++i;
+                } else {
+                    result.push_back(source[i] == '\n' ? '\n' : ' ');
+                }
+                continue;
+            }
+
+            if (source[i] == '/' && i + 1 < source.length()) {
+                if (source[i + 1] == '/') {
+                    inLineComment = true;
+                    result.append("  ");
+                    ++i;
+                    continue;
+                }
+                if (source[i + 1] == '*') {
+                    inBlockComment = true;
+                    result.append("  ");
+                    ++i;
+                    continue;
+                }
+            }
+
+            result.push_back(source[i]);
+        }
+
+        return result;
+    }
+
+    // Hoisted out of ParseComputeLocalSize: constructing a std::regex costs far more than
+    // running it over a small source, and it was being rebuilt on every compute compile. A
+    // const regex carries no mutable state, so sharing one instance across workers is safe.
+    static const std::regex kComputeLocalSizePattern(R"(local_size_([xyz])\s*=\s*([0-9]+))");
+
+    static ComputeLocalSize ParseComputeLocalSize(const MobileGL::String& source) {
+        ComputeLocalSize localSize;
+        const MobileGL::String uncommentedSource = StripGlslComments(source);
+
+        for (std::sregex_iterator it(uncommentedSource.begin(), uncommentedSource.end(), kComputeLocalSizePattern),
+             end;
+             it != end; ++it) {
+            const char axis = (*it)[1].str()[0];
+            // The [0-9]+ capture is unbounded, so `local_size_x = 99999999999999999999999`
+            // is a legal match. std::stoull would throw std::out_of_range on it and let the
+            // exception escape glCompileShader; std::from_chars reports the overflow instead.
+            // An overflowing literal saturates to UINT_MAX, which the device-limit check
+            // below rejects anyway - the same verdict a non-overflowing huge value gets.
+            const MobileGL::String digits = (*it)[2].str();
+            unsigned long long value = 0;
+            const std::from_chars_result parsed =
+                std::from_chars(digits.data(), digits.data() + digits.size(), value);
+            const MobileGL::Uint clampedValue = (parsed.ec != std::errc() || value > UINT_MAX)
+                                                    ? UINT_MAX
+                                                    : static_cast<MobileGL::Uint>(value);
+
+            // TODO: Replace this literal layout scanner with parser/AST-backed validation so expressions and
+            // specialization-id layouts are handled consistently with glslang.
+            localSize.declared = true;
+            if (axis == 'x') {
+                localSize.x = clampedValue;
+            } else if (axis == 'y') {
+                localSize.y = clampedValue;
+            } else {
+                localSize.z = clampedValue;
+            }
+        }
+
+        return localSize;
+    }
+
+    // The device limits come from the CompileEnv snapshot, never from a live driver query.
+    // GL_MAX_COMPUTE_WORK_GROUP_SIZE is a real GLES call on the DirectGLES backend: issued
+    // off the context thread it would silently no-op and turn a legal local_size_z into
+    // COMPILE_STATUS=FALSE. CaptureCompileEnv() issues it once, on the GL thread.
+    static std::optional<MobileGL::String> ValidateComputeLocalSizeLimits(
+        const MobileGL::String& source, const MobileGL::MG_Util::ShaderTranspiler::CompileEnv& env) {
+        const ComputeLocalSize localSize = ParseComputeLocalSize(source);
+        if (!localSize.declared) return std::nullopt;
+
+        if (localSize.x > env.maxComputeWorkGroupSize[0] || localSize.y > env.maxComputeWorkGroupSize[1] ||
+            localSize.z > env.maxComputeWorkGroupSize[2]) {
+            return "Compute shader local_size exceeds GL_MAX_COMPUTE_WORK_GROUP_SIZE.";
+        }
+
+        const unsigned long long invocations = static_cast<unsigned long long>(localSize.x) * localSize.y * localSize.z;
+        if (invocations > env.maxComputeWorkGroupInvocations) {
+            return "Compute shader local_size product exceeds GL_MAX_COMPUTE_WORK_GROUP_INVOCATIONS.";
+        }
+
+        return std::nullopt;
+    }
+
+    // The half of a compile that depends on nothing but the source text, the stage and the
+    // environment snapshot: preprocessing, the two lexical rejections, and the two lexical
+    // side-channel extractions. Split out so P0b layer 2 can memoize exactly this and
+    // nothing else - the glslang parse stays per-object because its TShader is consume-once.
+    // Deliberately free of any per-object state so the memo is sound.
+    //
+    // The compute local-size verdict reads `env` rather than the live backend, and
+    // env.fingerprint is part of the P0b cache key, so a memo can never be returned against
+    // limits other than the ones it was computed against.
+    static MobileGL::MG_State::GLState::ShaderPreprocessResult RunSourceOnlyPipeline(
+        const MobileGL::ShaderStage stage, const MobileGL::String& source,
+        const MobileGL::MG_Util::ShaderTranspiler::CompileEnv& env) {
+        using namespace MobileGL;
+        using namespace MobileGL::MG_Util::ShaderTranspiler;
+        using MobileGL::MG_State::GLState::ShaderPreprocessOutcome;
+
+        MobileGL::MG_State::GLState::ShaderPreprocessResult result;
+        result.preprocessedSource = source;
+        PreprocessShaderSource(stage, result.preprocessedSource, env);
+
+        if (stage == ShaderStage::Compute) {
+            if (const std::optional<String> localSizeError =
+                    ValidateComputeLocalSizeLimits(result.preprocessedSource, env)) {
+                result.outcome = ShaderPreprocessOutcome::ComputeLocalSizeRejected;
+                result.infoLog = *localSizeError;
+                return result;
+            }
+        }
+
+        if (const std::optional<String> reservedError = FindReservedIdentifierViolation(result.preprocessedSource)) {
+            result.outcome = ShaderPreprocessOutcome::ReservedIdentifierRejected;
+            result.infoLog = *reservedError;
+            return result;
+        }
+
+        // The parse this feeds runs in the link-compatible configuration (Vulkan-client
+        // env with relaxed rules): the TShader it produces is what glLinkProgram links and
+        // what the backends' SPIR-V is generated from - there is no second, GL-client
+        // parse. The GL frontend semantics the relaxed parse cannot provide are restored
+        // on top: explicit default-block uniform locations through the lexical
+        // side-channels below, dead-uniform/global-UBO filtering in
+        // ProgramObject::DoReflection.
+        result.explicitUniformLocations = ExtractExplicitUniformLocations(result.preprocessedSource);
+        result.explicitOpaqueBindings = ExtractExplicitOpaqueBindings(result.preprocessedSource);
+        result.outcome = ShaderPreprocessOutcome::Preprocessed;
+        return result;
+    }
+
+    // glslang has no "detach this thread" API in the vendored revision (there is no
+    // InitThread/DetachThread pair any more; thread attachment is implicit through
+    // thread_local state, and glslang::InitializeProcess() is process-wide, refcounted and
+    // mutex-guarded, so it needs no per-worker counterpart).
+    //
+    // What DOES need undoing is the thread pool allocator: TShader::parse sets the calling
+    // thread's TLS allocator to the shader's own pool and never restores it. Left pointing
+    // there, the next allocation this worker makes - in an unrelated job, or in glslang code
+    // reached from a different object - would come out of a pool the GL thread may already
+    // have deleted with the TShader. SetThreadPoolAllocator(nullptr) reverts the thread to
+    // its own thread_local default and is the documented idiom. A scope guard, so it also
+    // runs when a body throws.
+    struct GlslangThreadAllocatorGuard {
+        ~GlslangThreadAllocatorGuard() { glslang::SetThreadPoolAllocator(nullptr); }
+    };
+} // namespace
+
+namespace MobileGL::MG_State::GLState {
+    // Pure CPU work only. Everything this reads is either an input the node owns or a
+    // process-wide constant; everything it writes is `artifacts`. Do not add a GL/EGL call,
+    // a pActiveBackendObject read, or a pGLContext->RecordError() here - the first two are
+    // what CompileEnv exists to replace, and the third is why the design's section 6
+    // deferral mechanism (and JobNode's debug assert on it) exists.
+    void ShaderCompileTask::RunBody() {
+        // Own the failure rather than letting JobNode's backstop settle the node as
+        // Cancelled: an abandoned node publishes nothing, so the shader would report
+        // COMPILE_STATUS false with an EMPTY info log. GL models a failed compile as
+        // status + log, so turn a throw into exactly that - a completed job whose result
+        // is "this shader did not compile", with a log the application can read.
+        // (JobNode still catches: it is the last resort for anything below.)
+        try {
+            RunCompilePipeline();
+        } catch (const std::exception& e) {
+            artifacts = {};
+            artifacts.env = env;
+            artifacts.compileStatus = false;
+            artifacts.infoLog = std::format("Error: shader compilation failed: {}", e.what());
+        } catch (...) {
+            artifacts = {};
+            artifacts.env = env;
+            artifacts.compileStatus = false;
+            artifacts.infoLog = "Error: shader compilation failed: unknown exception";
+        }
+    }
+
+    void ShaderCompileTask::RunCompilePipeline() {
+        using namespace MG_Util::ShaderTranspiler;
+        const GlslangThreadAllocatorGuard glslangGuard;
+
+        const CompileEnv& compileEnv = *env;
+        artifacts.env = env;
+
+        // P0b layer 2: another shader object in this context may already have run the
+        // source-only half over byte-identical text under the same environment.
+        ShaderPreprocessResultPtr cached =
+            cache ? cache->Find(stage, sourceHash, *source, compileEnv.fingerprint) : nullptr;
+        SharedPtr<ShaderPreprocessResult> fresh;
+        if (!cached) fresh = MakeShared<ShaderPreprocessResult>(RunSourceOnlyPipeline(stage, *source, compileEnv));
+        const ShaderPreprocessResult& shared = cached ? *cached : *fresh;
+        const Bool shouldPopulateCache = !cached && cache != nullptr;
+
+        if (!shared.Preprocessed()) {
+            // Rejected lexically, or a glslang failure this context has already seen for
+            // this exact source (ParseFailed) - either way the parse can be skipped.
+            artifacts.infoLog = shared.infoLog;
+            if (shouldPopulateCache) {
+                cache->Insert(stage, sourceHash, *source, compileEnv.fingerprint, Move(fresh));
+            }
+            return;
+        }
+
+        ShaderAttrib attrib{.shaderType = MG_Util::ConvertShaderStageToGLEnum(stage),
+                            .sourceStr = shared.preprocessedSource,
+                            .flags = 0,
+                            .env = &compileEnv};
+
+        auto result = ShaderCompiler::CompileShader(attrib);
+        if (result) {
+            artifacts.compileStatus = true;
+            artifacts.shader = result.value();
+            // Copy, not move: `shared` may alias a cache entry that has to outlive us, and
+            // `fresh` is about to be handed to the cache.
+            artifacts.preprocessedSource = shared.preprocessedSource;
+            artifacts.explicitUniformLocations = shared.explicitUniformLocations;
+            artifacts.explicitOpaqueBindings = shared.explicitOpaqueBindings;
+            artifacts.infoLog.clear();
+            if (shouldPopulateCache) {
+                cache->Insert(stage, sourceHash, *source, compileEnv.fingerprint, Move(fresh));
+            }
+        } else {
+            artifacts.infoLog = result.error().log;
+            // Deferred, not logged here, for two reasons. MGLOG from a pool thread interleaves
+            // mid-line with the GL thread's own output and lands out of order relative to the
+            // glCompileShader that caused it; diagnostics.logLines is replayed by the join, on
+            // the GL thread, exactly where a serial implementation would have printed it.
+            // And a one-line summary rather than the old full source dump: a shaderpack stage
+            // is ~100KB, so the dump was the single largest thing this driver ever wrote to
+            // the log, for every failing shader. The info log is what names the offending
+            // line; the source is recoverable from the application.
+            const SizeT firstLineEnd = artifacts.infoLog.find('\n');
+            diagnostics.logLines.push_back(std::format(
+                "ShaderCompileTask: shader {} (stage {}) failed to compile; compileStatus = false. "
+                "Preprocessed source: {} bytes. First log line: {}",
+                externalIndex, static_cast<Int>(stage), shared.preprocessedSource.length(),
+                artifacts.infoLog.substr(0, firstLineEnd == String::npos ? artifacts.infoLog.length()
+                                                                        : firstLineEnd)));
+            if (shouldPopulateCache) {
+                fresh->outcome = ShaderPreprocessOutcome::ParseFailed;
+                fresh->infoLog = artifacts.infoLog;
+                fresh->explicitUniformLocations.clear();
+                fresh->explicitOpaqueBindings.clear();
+                cache->Insert(stage, sourceHash, *source, compileEnv.fingerprint, Move(fresh));
+            }
+        }
+    }
+} // namespace MobileGL::MG_State::GLState

MobileGL/MG_State/GLState/ProgramState/ShaderCompileTask.h

@@ -0,0 +1,83 @@
+// MobileGL - MobileGL/MG_State/GLState/ProgramState/ShaderCompileTask.h
+// Copyright (c) 2025-2026 MobileGL-Dev
+// Licensed under the GNU Lesser General Public License v3.0:
+//   https://www.gnu.org/licenses/gpl-3.0.txt
+//   https://www.gnu.org/licenses/lgpl-3.0.txt
+// SPDX-License-Identifier: LGPL-3.0-only
+// End of Source File Header
+
+#pragma once
+#include <Includes.h>
+#include <MG_Util/Async/JobNode.h>
+#include <MG_Util/ShaderTranspiler/CompileEnv.h>
+#include <MG_State/GLState/ProgramState/ShaderPreprocessCache.h>
+
+namespace MobileGL::MG_State::GLState {
+    // Everything one glCompileShader PRODUCES, in one block.
+    //
+    // This is exactly the set a single run of the compile pipeline writes, which is what
+    // makes "discard the artifacts" a complete invalidation and "move the artifacts" a
+    // complete publish. It lives on the job node rather than on ShaderObject: a worker fills
+    // it in, and the GL thread reads it through ShaderObject's join gate.
+    struct ShaderCompileArtifacts {
+        // The CompileEnv snapshot this compile ran against. Held so the consume-once
+        // re-parse in TakeShaderForLink() reproduces the original parse exactly, instead of
+        // re-reading whatever the backend says now.
+        SharedPtr<const MG_Util::ShaderTranspiler::CompileEnv> env;
+        SharedPtr<glslang::TShader> shader;
+        // The source the parse actually consumed (after PreprocessShaderSource), kept for
+        // TakeShaderForLink's re-parse so a later link never depends on the preprocessor
+        // being deterministic across backend-state changes.
+        String preprocessedSource;
+        UnorderedMap<String, Int> explicitUniformLocations;
+        UnorderedMap<String, Uint> explicitOpaqueBindings;
+        // GL-thread-owned, and the one field here a worker never touches: TakeShaderForLink
+        // flips it after the join. Stage 4 replaces it with an atomic claim on this node,
+        // because two ProgramLinkTasks for two programs sharing this shader can then race
+        // for the parse on two workers.
+        Bool shaderConsumedByLink = false;
+        String infoLog;
+        Bool compileStatus = false;
+    };
+
+    // The unit of asynchronous shader compilation: one glCompileShader's worth of pure CPU
+    // work - preprocess, the two lexical rejections, the two lexical extractions, and the
+    // glslang parse - with every input it needs owned by the node itself.
+    //
+    // That ownership is the whole point. The node reads no GL-thread state (the source is a
+    // SharedPtr<const String> snapshot, the device limits come from the CompileEnv snapshot,
+    // the P0b cross-object memo is shared-owned and internally locked) and writes nothing
+    // but its own `artifacts`. So a node whose ShaderObject was re-sourced, deleted, or
+    // destroyed while it was still running is safe to simply abandon - no wait, no
+    // synchronization with the GL thread beyond the node's own terminal state.
+    class ShaderCompileTask final : public MG_Util::Async::JobNode {
+    public:
+        ShaderCompileTask(const ShaderStage stage, SharedPtr<const String> source, const Uint64 sourceHash,
+                          SharedPtr<const MG_Util::ShaderTranspiler::CompileEnv> env,
+                          SharedPtr<ShaderPreprocessCache> cache, const Uint externalIndex)
+            : stage(stage), source(Move(source)), sourceHash(sourceHash), env(Move(env)), cache(Move(cache)),
+              externalIndex(externalIndex) {}
+
+        // ---- inputs: immutable after construction, all owned by the node ----
+        const ShaderStage stage;
+        // The exact text at enqueue. ShaderObject compares this pointer against its own
+        // m_source to decide whether its layer-1 memo is armed, which is why glShaderSource
+        // only ever swaps the pointer when the text genuinely differs.
+        const SharedPtr<const String> source;
+        const Uint64 sourceHash;
+        const SharedPtr<const MG_Util::ShaderTranspiler::CompileEnv> env;
+        // P0b layer 2, or null. Null is the "no context" case (the default fragment shader,
+        // the backends' internal blit/mipmap shaders) and doubles as the marker for
+        // "compile inline regardless of the async flag" - see ShaderObject::Compile().
+        const SharedPtr<ShaderPreprocessCache> cache;
+        const Uint externalIndex; // logs only
+
+        // ---- output: valid iff IsComplete(), immutable afterwards ----
+        ShaderCompileArtifacts artifacts;
+
+    private:
+        void RunBody() override;
+        // The real body; RunBody wraps it so a throw becomes a GL-visible compile failure.
+        void RunCompilePipeline();
+    };
+} // namespace MobileGL::MG_State::GLState

MobileGL/MG_State/GLState/ProgramState/ShaderObject.cpp

@@ -8,313 +8,127 @@
 
 #include "ShaderObject.h"
 #include "ShaderPreprocessCache.h"
-#include <MG_Util/ShaderTranspiler/Types.h>
-#include <MG_Util/ShaderTranspiler/ShaderCompiler.h>
+#include <MG_Util/Async/ShaderCompilePool.h>
 #include <MG_Util/Converters/MGToGL/ProgramEnumConverter.h>
-#include <MG_Util/ShaderTranspiler/ShaderSourceProcessor.h>
 #include <MG_Util/ShaderTranspiler/CompileEnv.h>
-#include <MG_Util/ShaderTranspiler/glslang/UniformTraverser.h>
-
-#include <charconv>
-
-namespace {
-    struct ComputeLocalSize {
-        MobileGL::Uint x = 1;
-        MobileGL::Uint y = 1;
-        MobileGL::Uint z = 1;
-        bool declared = false;
-    };
-
-    static MobileGL::String StripGlslComments(const MobileGL::String& source) {
-        MobileGL::String result;
-        result.reserve(source.length());
-
-        bool inLineComment = false;
-        bool inBlockComment = false;
-        for (MobileGL::SizeT i = 0; i < source.length(); ++i) {
-            if (inLineComment) {
-                if (source[i] == '\n') {
-                    inLineComment = false;
-                    result.push_back(source[i]);
-                } else {
-                    result.push_back(' ');
-                }
-                continue;
-            }
-
-            if (inBlockComment) {
-                if (source[i] == '*' && i + 1 < source.length() && source[i + 1] == '/') {
-                    inBlockComment = false;
-                    result.append("  ");
-                    ++i;
-                } else {
-                    result.push_back(source[i] == '\n' ? '\n' : ' ');
-                }
-                continue;
-            }
-
-            if (source[i] == '/' && i + 1 < source.length()) {
-                if (source[i + 1] == '/') {
-                    inLineComment = true;
-                    result.append("  ");
-                    ++i;
-                    continue;
-                }
-                if (source[i + 1] == '*') {
-                    inBlockComment = true;
-                    result.append("  ");
-                    ++i;
-                    continue;
-                }
-            }
-
-            result.push_back(source[i]);
-        }
-
-        return result;
-    }
-
-    // Hoisted out of ParseComputeLocalSize: constructing a std::regex costs far more than
-    // running it over a small source, and it was being rebuilt on every compute compile. A
-    // const regex carries no mutable state, so sharing one instance is safe.
-    static const std::regex kComputeLocalSizePattern(R"(local_size_([xyz])\s*=\s*([0-9]+))");
-
-    static ComputeLocalSize ParseComputeLocalSize(const MobileGL::String& source) {
-        ComputeLocalSize localSize;
-        const MobileGL::String uncommentedSource = StripGlslComments(source);
-
-        for (std::sregex_iterator it(uncommentedSource.begin(), uncommentedSource.end(), kComputeLocalSizePattern),
-             end;
-             it != end; ++it) {
-            const char axis = (*it)[1].str()[0];
-            // The [0-9]+ capture is unbounded, so `local_size_x = 99999999999999999999999`
-            // is a legal match. std::stoull would throw std::out_of_range on it and let the
-            // exception escape glCompileShader; std::from_chars reports the overflow instead.
-            // An overflowing literal saturates to UINT_MAX, which the device-limit check
-            // below rejects anyway - the same verdict a non-overflowing huge value gets.
-            const MobileGL::String digits = (*it)[2].str();
-            unsigned long long value = 0;
-            const std::from_chars_result parsed =
-                std::from_chars(digits.data(), digits.data() + digits.size(), value);
-            const MobileGL::Uint clampedValue = (parsed.ec != std::errc() || value > UINT_MAX)
-                                                    ? UINT_MAX
-                                                    : static_cast<MobileGL::Uint>(value);
-
-            // TODO: Replace this literal layout scanner with parser/AST-backed validation so expressions and
-            // specialization-id layouts are handled consistently with glslang.
-            localSize.declared = true;
-            if (axis == 'x') {
-                localSize.x = clampedValue;
-            } else if (axis == 'y') {
-                localSize.y = clampedValue;
-            } else {
-                localSize.z = clampedValue;
-            }
-        }
-
-        return localSize;
-    }
-
-    // The device limits come from the CompileEnv snapshot, never from a live driver query.
-    // GL_MAX_COMPUTE_WORK_GROUP_SIZE is a real GLES call on the DirectGLES backend: issued
-    // off the context thread it would silently no-op and turn a legal local_size_z into
-    // COMPILE_STATUS=FALSE. CaptureCompileEnv() issues it once, on the GL thread.
-    static std::optional<MobileGL::String> ValidateComputeLocalSizeLimits(
-        const MobileGL::String& source, const MobileGL::MG_Util::ShaderTranspiler::CompileEnv& env) {
-        const ComputeLocalSize localSize = ParseComputeLocalSize(source);
-        if (!localSize.declared) return std::nullopt;
-
-        if (localSize.x > env.maxComputeWorkGroupSize[0] || localSize.y > env.maxComputeWorkGroupSize[1] ||
-            localSize.z > env.maxComputeWorkGroupSize[2]) {
-            return "Compute shader local_size exceeds GL_MAX_COMPUTE_WORK_GROUP_SIZE.";
-        }
-
-        const unsigned long long invocations = static_cast<unsigned long long>(localSize.x) * localSize.y * localSize.z;
-        if (invocations > env.maxComputeWorkGroupInvocations) {
-            return "Compute shader local_size product exceeds GL_MAX_COMPUTE_WORK_GROUP_INVOCATIONS.";
-        }
-
-        return std::nullopt;
-    }
-
-    // The half of ShaderObject::Compile() that depends on nothing but the source text and
-    // the stage: preprocessing, the two lexical rejections, and the two lexical
-    // side-channel extractions. Split out so P0b layer 2 can memoize exactly this and
-    // nothing else - the glslang parse stays per-object because its TShader is
-    // consume-once. Deliberately free of any per-object state so the memo is sound.
-    //
-    // The former caveat is gone: the compute local-size verdict reads `env` rather than the
-    // live backend, and env.fingerprint is part of the P0b cache key, so a memo can never be
-    // returned against limits other than the ones it was computed against.
-    static MobileGL::MG_State::GLState::ShaderPreprocessResult RunSourceOnlyPipeline(
-        const MobileGL::ShaderStage stage, const MobileGL::String& source,
-        const MobileGL::MG_Util::ShaderTranspiler::CompileEnv& env) {
-        using namespace MobileGL;
-        using namespace MobileGL::MG_Util::ShaderTranspiler;
-        using MobileGL::MG_State::GLState::ShaderPreprocessOutcome;
-
-        MobileGL::MG_State::GLState::ShaderPreprocessResult result;
-        result.preprocessedSource = source;
-        PreprocessShaderSource(stage, result.preprocessedSource, env);
-
-        if (stage == ShaderStage::Compute) {
-            if (const std::optional<String> localSizeError =
-                    ValidateComputeLocalSizeLimits(result.preprocessedSource, env)) {
-                result.outcome = ShaderPreprocessOutcome::ComputeLocalSizeRejected;
-                result.infoLog = *localSizeError;
-                return result;
-            }
-        }
-
-        if (const std::optional<String> reservedError = FindReservedIdentifierViolation(result.preprocessedSource)) {
-            result.outcome = ShaderPreprocessOutcome::ReservedIdentifierRejected;
-            result.infoLog = *reservedError;
-            return result;
-        }
-
-        // The parse this feeds runs in the link-compatible configuration (Vulkan-client
-        // env with relaxed rules): the TShader it produces is what glLinkProgram links and
-        // what the backends' SPIR-V is generated from - there is no second, GL-client
-        // parse. The GL frontend semantics the relaxed parse cannot provide are restored
-        // on top: explicit default-block uniform locations through the lexical
-        // side-channels below, dead-uniform/global-UBO filtering in
-        // ProgramObject::DoReflection.
-        result.explicitUniformLocations = ExtractExplicitUniformLocations(result.preprocessedSource);
-        result.explicitOpaqueBindings = ExtractExplicitOpaqueBindings(result.preprocessedSource);
-        result.outcome = ShaderPreprocessOutcome::Preprocessed;
-        return result;
-    }
-}
+#include <MG_Util/ShaderTranspiler/ShaderCompiler.h>
+#include <MG_Util/ShaderTranspiler/Types.h>
 
 namespace MobileGL::MG_State::GLState {
     void ShaderObject::SetShaderSource(const String& source) {
         // P0b layer 1. glShaderSource always REPLACES the source, but replacing it with a
         // byte-identical one cannot change what a compile would produce: the whole
-        // pipeline below (preprocess -> lexical checks -> glslang parse) is a pure
-        // function of (stage, source) plus context-lifetime backend limits. So keeping the
-        // compiled state is not an optimization that changes observable behaviour - the
-        // COMPILE_STATUS, the info log and the reflection a caller can query are exactly
-        // what a real recompile would have rebuilt, byte for byte.
+        // pipeline (preprocess -> lexical checks -> glslang parse) is a pure function of
+        // (stage, source, CompileEnv). So keeping the compiled state is not an optimization
+        // that changes observable behaviour - the COMPILE_STATUS, the info log and the
+        // reflection a caller can query are exactly what a real recompile would have
+        // rebuilt, byte for byte. A compile still IN FLIGHT is left running for the same
+        // reason: it is computing the right answer for text this object still holds.
         if (SourceMatchesCompiledState(source)) return;
-        m_source = source;
+        // The text genuinely changed, so whatever a running job is computing is now about
+        // an old source. Drop it where it stands - it owns its own copy of that old string,
+        // so swapping the pointer below cannot race its storage.
+        CancelCompile();
+        m_source = MakeShared<const String>(source);
         InvalidateCompiledState();
     }
 
     void ShaderObject::SetShaderSource(String&& source) {
         if (SourceMatchesCompiledState(source)) return;
-        m_source = Move(source);
+        CancelCompile();
+        m_source = MakeShared<const String>(Move(source));
         InvalidateCompiledState();
     }
 
     Bool ShaderObject::SourceMatchesCompiledState(const String& candidate) const {
-        if (!m_hasCompiledState) return false;
-        if (candidate.length() != m_compiledSourceLength) return false;
-        if (ShaderPreprocessCache::HashSource(candidate) != m_compiledSourceHash) return false;
-        // The hash is a fast reject only; confirm against the actual stored text. While
-        // m_hasCompiledState holds, m_source IS the source that produced the state.
-        return candidate == m_source;
+        // The memo is armed exactly while a job exists that was built from the string this
+        // object still points at - pending or finished, success or failure.
+        if (!HasMemoizedCompile()) return false;
+        if (candidate.length() != m_source->length()) return false;
+        // Never let correctness ride on a hash: the answer is the full text comparison.
+        // (The stored hash on the node is a cache-lookup accelerator, not a substitute.)
+        return candidate == *m_source;
     }
 
-    void ShaderObject::RememberCompiledSource(const Uint64 sourceHash) {
-        m_hasCompiledState = true;
-        m_compiledSourceHash = sourceHash;
-        m_compiledSourceLength = m_source.length();
+    void ShaderObject::JoinPendingCompile() const {
+        MOBILEGL_ASSERT(!MG_Util::Async::ShaderCompilePool::IsPoolThread(),
+                        "ShaderObject::EnsureCompileJoined() reached from a pool thread; a job body must never read "
+                        "GL-thread-owned objects");
+        m_compiled->Wait();
+        m_compileJoined = true;
+        // Errors and worker-side log lines are raised HERE, on the GL thread, at the first
+        // join of the job that produced them - which for a single shader is trivially the
+        // order a serial implementation would have produced them in.
+        MG_Util::Async::ApplyDeferredDiagnostics(*m_compiled);
+        // A node that settled as Cancelled published nothing. Dropping it here is what keeps
+        // the object's state machine to two reachable cases - "no job" and "a job that
+        // completed" - so every reader below can treat a live node as authoritative.
+        if (!m_compiled->IsComplete()) m_compiled.reset();
     }
 
-    // EnsureCompileJoined() is defined inline in ShaderObject.h (see the comment there for
-    // why: no LTO, and it is called from every Compiled() read).
-
     void ShaderObject::InvalidateCompiledState() {
-        // The compile artifacts are exactly what one Compile() writes, so discarding them
-        // wholesale IS the invalidation. (Kept as an explicit reset rather than a
-        // default-construct so the intent survives a future field addition.)
-        Compiled() = CompileArtifacts{};
-        m_hasCompiledState = false;
-        m_compiledSourceHash = 0;
-        m_compiledSourceLength = 0;
+        // The job node holds exactly what one Compile() produces, so discarding it IS the
+        // invalidation - and it re-arms nothing, so the next Compile() genuinely recompiles.
+        m_compiled.reset();
+    }
+
+    void ShaderObject::CancelCompile() {
+        if (!m_compiled || m_compiled->IsTerminal()) return;
+        // Cooperative and non-blocking. A node that no worker has picked up settles
+        // immediately; one that is running is flagged and settles when its body returns,
+        // writing only into itself the whole time.
+        m_compiled->Cancel();
+        m_compiled.reset();
     }
 
     void ShaderObject::Compile() {
-        using namespace MG_Util::ShaderTranspiler;
-
-        // P0b layer 1: the state this object holds was produced by a previous Compile() of
-        // the exact source it still holds, so a recompile is a no-op. This covers the
-        // failure case too - the info log stays queryable because nothing is cleared.
+        // P0b layer 1, as a tri-state: the memo is "the node in m_compiled was built from
+        // the string m_source still points at". SetShaderSource only swaps that pointer when
+        // the text actually differs, so this is a pointer compare, and it covers Pending as
+        // well as Complete - a second glCompileShader on an in-flight object is a no-op, not
+        // a duplicate job racing to write the same fields.
         //
-        // shaderConsumedByLink interaction: if the stored TShader already fed a link,
-        // the no-op leaves preprocessedSource and both side-channel maps intact, which
-        // is precisely what TakeShaderForLink's on-demand re-parse needs. A real recompile
-        // would have handed the next link a fresh parse; the no-op hands it a fresh
-        // re-parse of the identical source instead. Same result, one parse either way.
-        if (m_hasCompiledState) return;
+        // The failure case is covered too: the info log stays queryable because nothing is
+        // cleared. And if the stored TShader already fed a link, the no-op leaves
+        // preprocessedSource and both side-channel maps intact, which is precisely what
+        // TakeShaderForLink's on-demand re-parse needs - a real recompile would have handed
+        // the next link a fresh parse, the no-op hands it a fresh re-parse of the identical
+        // source instead. Same result, one parse either way.
+        if (HasMemoizedCompile()) return;
 
-        InvalidateCompiledState();
+        // The compile-environment snapshot is taken HERE, on the GL thread, and handed to
+        // the job. Everything the pipeline needs to know about the device comes through it,
+        // never through pActiveBackendObject - that is what makes the body movable.
+        m_compiled = MakeShared<ShaderCompileTask>(m_stage, m_source, ShaderPreprocessCache::HashSource(*m_source),
+                                                   MG_Util::ShaderTranspiler::GetCurrentCompileEnv(),
+                                                   m_preprocessCache, m_externalIndex);
+        m_compileJoined = false;
 
-        const Uint64 sourceHash = ShaderPreprocessCache::HashSource(m_source);
-
-        // The compile-environment snapshot, taken here on the GL thread. Everything below
-        // reads the device through it and never through pActiveBackendObject, which is what
-        // makes the whole body movable onto a worker in stage 3.
-        CompileArtifacts& compiled = Compiled();
-        compiled.env = MG_Util::ShaderTranspiler::GetCurrentCompileEnv();
-        const MG_Util::ShaderTranspiler::CompileEnv& env = *compiled.env;
-
-        // P0b layer 2: another shader object in this context may already have run the
-        // source-only half over byte-identical text under the same environment.
-        ShaderPreprocessResultPtr cached =
-            m_preprocessCache ? m_preprocessCache->Find(m_stage, sourceHash, m_source, env.fingerprint) : nullptr;
-        SharedPtr<ShaderPreprocessResult> fresh;
-        if (!cached) fresh = MakeShared<ShaderPreprocessResult>(RunSourceOnlyPipeline(m_stage, m_source, env));
-        const ShaderPreprocessResult& shared = cached ? *cached : *fresh;
-        const Bool shouldPopulateCache = !cached && m_preprocessCache != nullptr;
-
-        if (!shared.Preprocessed()) {
-            // Rejected lexically, or a glslang failure this context has already seen for
-            // this exact source (ParseFailed) - either way the parse can be skipped.
-            compiled.infoLog = shared.infoLog;
-            if (shouldPopulateCache) {
-                m_preprocessCache->Insert(m_stage, sourceHash, m_source, env.fingerprint, Move(fresh));
-            }
-            RememberCompiledSource(sourceHash);
+        // Two reasons to stay on this thread, one rule. Without the async flag the whole
+        // path must be byte-identical to the synchronous implementation, and a cache-less
+        // object is an internal shader that compiles and reads its status in the same
+        // breath (see the constructor comment) - a job would only add a round trip.
+        if (!m_preprocessCache || !MG_Util::Async::AsyncShaderCompileEnabled()) {
+            m_compiled->RunInline();
+            // Inline means the node is already terminal, so this join only replays
+            // diagnostics; it is here so the synchronous and asynchronous paths publish
+            // through the identical code.
+            EnsureCompileJoined();
             return;
         }
-
-        ShaderAttrib attrib{.shaderType = MG_Util::ConvertShaderStageToGLEnum(m_stage),
-                            .sourceStr = shared.preprocessedSource,
-                            .flags = 0,
-                            .env = &env};
-
-        auto result = ShaderCompiler::CompileShader(attrib);
-        if (result) {
-            compiled.compileStatus = true;
-            compiled.shader = result.value();
-            // Copy, not move: `shared` may alias a cache entry that has to outlive us, and
-            // `fresh` is about to be handed to the cache.
-            compiled.preprocessedSource = shared.preprocessedSource;
-            compiled.explicitUniformLocations = shared.explicitUniformLocations;
-            compiled.explicitOpaqueBindings = shared.explicitOpaqueBindings;
-            compiled.infoLog.clear();
-            if (shouldPopulateCache) {
-                m_preprocessCache->Insert(m_stage, sourceHash, m_source, env.fingerprint, Move(fresh));
-            }
-        } else {
-            compiled.infoLog = result.error().log;
-            MGLOG_D("ShaderObject::Compile: Shader %d compilation failed.\nSource:\n%s\nInfoLog:\n%s\nSetting "
-                    "compileStatus = false as a result.",
-                    m_externalIndex, shared.preprocessedSource.c_str(), compiled.infoLog.c_str());
-            if (shouldPopulateCache) {
-                fresh->outcome = ShaderPreprocessOutcome::ParseFailed;
-                fresh->infoLog = compiled.infoLog;
-                fresh->explicitUniformLocations.clear();
-                fresh->explicitOpaqueBindings.clear();
-                m_preprocessCache->Insert(m_stage, sourceHash, m_source, env.fingerprint, Move(fresh));
-            }
-        }
-        RememberCompiledSource(sourceHash);
+        MG_Util::Async::ShaderCompilePool::Get().Post(m_compiled);
     }
 
     SharedPtr<glslang::TShader> ShaderObject::TakeShaderForLink(String& outReparseLog) {
-        CompileArtifacts& compiled = Compiled();
+        EnsureCompileJoined();
+        // Unreachable through the GL frontend: callers gate on GetCompileStatus().
+        if (!m_compiled) return nullptr;
+
+        // Mutating the node's artifacts from here is legal precisely because the node is
+        // terminal by now: no worker will ever touch it again, and this thread is the GL
+        // thread. Stage 4, where two link JOBS can reach the same node concurrently,
+        // replaces this flag with an atomic claim on the node.
+        ShaderCompileArtifacts& compiled = m_compiled->artifacts;
         if (compiled.shader && !compiled.shaderConsumedByLink) {
             compiled.shaderConsumedByLink = true;
             return compiled.shader;

MobileGL/MG_State/GLState/ProgramState/ShaderObject.h

@@ -8,39 +8,47 @@
 
 #pragma once
 #include <Includes.h>
-#include <MG_Util/ShaderTranspiler/CompileEnv.h>
+#include <MG_State/GLState/ProgramState/ShaderStage.h>
+#include <MG_State/GLState/ProgramState/ShaderCompileTask.h>
 
 namespace MobileGL {
-    enum class ShaderStage {
-        Vertex,
-        TessControl,
-        TessEval,
-        Geometry,
-        Fragment,
-        Compute,
-        ShaderStageCount,
-        Unknown = -1
-    };
-
     namespace MG_State::GLState {
-        // P0b layer 2. Declared, not included: the cache keys on ShaderStage, so including
-        // its header here would be circular.
-        class ShaderPreprocessCache;
-
+        // The GL-visible shader name. It owns the source text and one compile job node; the
+        // job node owns everything a compile produces.
+        //
+        // Every member below is GL-thread-owned, and every read of worker-produced state
+        // goes through Compiled(), which joins first. That is invariant I5 of the P1 design:
+        // because Compiled() is the SOLE accessor of the node's artifacts, the compiler
+        // enumerates every reader for us and none can be forgotten.
         class ShaderObject {
         public:
-            // `preprocessCache` is the owning context's cross-object memo (P0b layer 2);
-            // null is fully supported and simply means "no sharing" - that is what the
-            // context-less internal shader objects (the default FS, the blit pipeline) use.
-            // Shared ownership rather than a raw pointer: once compiles run on a worker the
-            // job outlives neither the object nor the context deterministically, and the
-            // cache has to stay alive for whoever is still reading it.
+            // `preprocessCache` is the owning context's cross-object memo (P0b layer 2).
+            // Null is fully supported and means two things at once: "no sharing", and
+            // "compile inline, never on a worker". Those coincide exactly - the only
+            // cache-less shader objects are the internal ones (ProgramObject's default
+            // fragment shader, the DirectVulkan blit and depth-mipmap shaders) and every one
+            // of them compiles and reads its status in the same breath, so a job would only
+            // add a round trip. Shared ownership rather than a raw pointer: a compile job
+            // outlives neither the object nor the context deterministically, and the cache
+            // has to stay alive for whoever is still reading it.
             ShaderObject(const ShaderStage stage, Uint externalIndex,
                          SharedPtr<ShaderPreprocessCache> preprocessCache = nullptr)
                 : m_stage(stage), m_externalIndex(externalIndex), m_preprocessCache(Move(preprocessCache)) {}
+            // Cancel-not-join: the node owns its inputs, so an in-flight compile whose
+            // object just went away is safe to abandon where it stands. Nothing can observe
+            // its result any more - this object was the only route to it.
+            ~ShaderObject() { CancelCompile(); }
+
+            ShaderObject(const ShaderObject&) = delete;
+            ShaderObject& operator=(const ShaderObject&) = delete;
+
             void SetShaderSource(const String& source);
             void SetShaderSource(String&& source);
             void Compile();
+            // Drops a compile that is still in flight, without waiting for it. Called at the
+            // points where the object's compiled state stops being observable: a real source
+            // change, and the release of an orphaned shader name.
+            void CancelCompile();
             void MarkAsDeleted();
 
             // Hands out a link-consumable TShader. glslang's mapIO mutates the TShader's
@@ -54,10 +62,14 @@ namespace MobileGL {
 
             Uint GetExternalIndex() const { return m_externalIndex; }
             ShaderStage GetShaderStage() const { return m_stage; }
-            const String& GetShaderSource() const { return m_source; }
+            // No join: the source is GL-thread-owned, and a worker only ever reads the
+            // immutable snapshot it was handed at enqueue.
+            const String& GetShaderSource() const { return *m_source; }
+            // The snapshot itself, for whoever needs to hand it to a job.
+            const SharedPtr<const String>& GetShaderSourcePtr() const { return m_source; }
+
             const SharedPtr<glslang::TShader>& GetCompiledShader() const { return Compiled().shader; }
             const String& GetInfoLog() const { return Compiled().infoLog; }
-            const UnorderedMap<String, Uint>& GetUniformLocations() const { return Compiled().uniforms; }
             // Explicit layout(location = N) qualifiers on this shader's default-block
             // uniforms, captured lexically at Compile() because the relaxed parse drops
             // them from reflection (see ExtractExplicitUniformLocations).
@@ -73,96 +85,98 @@ namespace MobileGL {
             Bool GetCompileStatus() const { return Compiled().compileStatus; }
             Bool GetDeleteStatus() const { return m_deleteStatus; }
 
-            // Blocks until a pending compile (P1 stage 3 onwards) has published its
-            // artifacts. Public for the few sites that must join without reading anything.
-            // A no-op today - nothing is ever pending.
+            // Blocks until a pending compile has published its artifacts. Public for the
+            // sites that must join without reading anything - ProgramObject::Link's
+            // prologue, which needs every attached shader settled before it runs.
             void JoinCompile() const { EnsureCompileJoined(); }
 
-            // True while this object holds the outcome (success OR failure) of a previous
-            // Compile() of exactly the source it currently holds - i.e. while the P0b
-            // layer-1 memo is armed and a glCompileShader would be a no-op. Diagnostics
-            // and tests only; nothing in the GL frontend branches on it.
+            // True while this object holds the outcome (success OR failure) of a Compile()
+            // of exactly the source it currently holds - i.e. while the P0b layer-1 memo is
+            // armed and a glCompileShader would be a no-op. Diagnostics and tests only;
+            // nothing in the GL frontend branches on it.
             //
-            // Deliberately does NOT join: the memo bookkeeping below is GL-thread-owned and
-            // says nothing about whether a worker has finished, which is exactly the
-            // property GL_COMPLETION_STATUS_KHR needs when stage 3 lands.
-            Bool HasMemoizedCompile() const { return m_hasCompiledState; }
+            // Tri-state, and deliberately NOT joining: an in-flight compile of the current
+            // source counts as memoized (a second glCompileShader must not enqueue a
+            // duplicate job), but asking that question must never block.
+            // A node that settled as Cancelled (the job body threw, or the enqueue failed)
+            // carries no result, so it must NOT satisfy the memo: otherwise a second
+            // glCompileShader on the same source enqueues nothing and the eventual join
+            // reports GL_FALSE forever. The synchronous path retries in exactly this case.
+            Bool HasMemoizedCompile() const {
+                return m_compiled != nullptr && m_compiled->source == m_source && !m_compiled->IsCancelled();
+            }
+
+            // MUST NOT JOIN - this is what GL_COMPLETION_STATUS_KHR will read when the
+            // extension surface lands. "No job at all" counts as complete: there is nothing
+            // outstanding to wait for.
+            Bool IsCompileComplete() const { return m_compiled == nullptr || m_compiled->IsTerminal(); }
 
         private:
-            // ---- P1: everything a compile PRODUCES, in one block ----
-            //
-            // Same rule as ProgramObject::LinkArtifacts: this is exactly what
-            // InvalidateCompiledState() clears, i.e. exactly what one run of Compile()
-            // writes. Stage 3 lifts this struct wholesale into ShaderCompileTask, where a
-            // worker fills it in and the GL thread reads it through the same gate.
-            struct CompileArtifacts {
-                // The CompileEnv snapshot this compile ran against. Held so the
-                // consume-once re-parse in TakeShaderForLink() reproduces the original
-                // parse exactly, instead of re-reading whatever the backend says now.
-                SharedPtr<const MG_Util::ShaderTranspiler::CompileEnv> env;
-                SharedPtr<glslang::TShader> shader;
-                // The source Compile() actually parsed (after PreprocessShaderSource), kept
-                // for TakeShaderForLink's re-parse so a later link never depends on the
-                // preprocessor being deterministic across backend-state changes.
-                String preprocessedSource;
-                UnorderedMap<String, Uint> uniforms;
-                UnorderedMap<String, Int> explicitUniformLocations;
-                UnorderedMap<String, Uint> explicitOpaqueBindings;
-                Bool shaderConsumedByLink = false;
-                String infoLog;
-                Bool compileStatus = false;
-            };
-
             // ---- The one and only join gate for compile output (P1 invariant I5) ----
-            // Blocks until a pending compile has published into m_compiled. Today nothing
-            // is ever pending - glCompileShader still runs the whole body inline - so this
-            // is an unconditional no-op. It exists NOW so that every reader of compile
-            // output is already routed through it when stage 3 makes it block.
+            // The fast path - no job, or a job whose result this object has already pulled -
+            // is two predictable branches and stays inline: it runs on every Compiled() read
+            // and the project never builds with LTO, so an out-of-line body would be a real
+            // cross-TU call at each of those sites. The blocking half is out of line.
             //
-            // Defined inline (not in ShaderObject.cpp): called from every Compiled() read,
-            // and the project never builds with LTO, so an out-of-line empty body would be
-            // a real cross-TU call at each of those call sites instead of folding away.
-            void EnsureCompileJoined() const {}
-            CompileArtifacts& Compiled() {
-                EnsureCompileJoined();
-                return m_compiled;
+            // The gate keys on "has this object pulled the job's result yet", NOT on "is the
+            // job terminal". Those differ in the case that matters: a worker can finish a
+            // compile before the GL thread ever looks at it, and the pull is where deferred
+            // diagnostics get replayed and an abandoned node gets dropped. Keying on
+            // terminality would silently skip both.
+            void EnsureCompileJoined() const {
+                if (m_compiled && !m_compileJoined) JoinPendingCompile();
             }
-            const CompileArtifacts& Compiled() const {
+            void JoinPendingCompile() const;
+
+            // The artifacts of a compile that ran to completion. A node that was abandoned
+            // (cancelled at teardown, or whose body threw) never publishes: JoinPendingCompile
+            // drops it, so anything reachable here is either Complete or absent, and "absent"
+            // reads as the never-compiled defaults - COMPILE_STATUS false, empty info log,
+            // which is exactly what GL requires before the first glCompileShader.
+            static const ShaderCompileArtifacts& EmptyArtifacts() {
+                static const ShaderCompileArtifacts empty;
+                return empty;
+            }
+            const ShaderCompileArtifacts& Compiled() const {
                 EnsureCompileJoined();
-                return m_compiled;
+                return m_compiled ? m_compiled->artifacts : EmptyArtifacts();
             }
 
             void InvalidateCompiledState();
             // ---- P0b layer 1: per-object no-op recompile ----
-            // True iff `candidate` is byte-identical to the source that produced the
-            // compiled state this object is currently holding. The stored hash and length
-            // are only a fast reject; the answer is always confirmed against the full
-            // stored text, so no behaviour rides on a 64-bit hash.
+            // True iff `candidate` is byte-identical to the source that produced (or is
+            // producing) the compiled state this object currently holds.
             Bool SourceMatchesCompiledState(const String& candidate) const;
-            // Arms the layer-1 memo for the source that Compile() just processed.
-            void RememberCompiledSource(Uint64 sourceHash);
 
             // ---- GL-thread-owned state: never produced by a compile, so it never joins ----
-            const Uint m_externalIndex = 0;
             const ShaderStage m_stage;
-            // glShaderSource text. A worker only ever reads the snapshot handed to it, so
-            // GL_SHADER_SOURCE_LENGTH and glGetShaderSource never join.
-            String m_source;
+            const Uint m_externalIndex = 0;
+            // The pre-glShaderSource state, shared by every untouched object rather than
+            // allocated per glCreateShader.
+            static const SharedPtr<const String>& EmptySource() {
+                static const SharedPtr<const String> empty = MakeShared<const String>();
+                return empty;
+            }
+            // glShaderSource text, as an immutable snapshot. Never null. A job holds its own
+            // SharedPtr to the exact string it was given, so replacing the source under a
+            // running compile cannot race its storage - and the layer-1 memo collapses to a
+            // pointer comparison against the job's snapshot, because the setter only swaps
+            // the pointer when the text genuinely differs.
+            SharedPtr<const String> m_source = EmptySource();
 
-            // P0b layer 2: the owning context's cross-object memo, or null.
+            // P0b layer 2: the owning context's cross-object memo, or null. Internally
+            // locked, because several workers hit it at once.
             const SharedPtr<ShaderPreprocessCache> m_preprocessCache;
-            // P0b layer 1. m_hasCompiledState is the invariant "m_source is byte-identical
-            // to the source that produced the compile artifacts"; it is armed at the end of
-            // every Compile() and disarmed by InvalidateCompiledState(). Stage 3 replaces
-            // all three with a pointer compare against the in-flight job's source snapshot.
-            Bool m_hasCompiledState = false;
-            Uint64 m_compiledSourceHash = 0;
-            SizeT m_compiledSourceLength = 0;
 
             Bool m_deleteStatus = false;
 
-            // ---- Compile OUTPUT ---- reachable only through Compiled().
-            CompileArtifacts m_compiled;
+            // ---- Compile OUTPUT ---- pending OR completed; reachable only through Compiled().
+            // Mutable because the join is a read-side operation: a const getter has to be
+            // able to settle an outstanding job before answering.
+            mutable SharedPtr<ShaderCompileTask> m_compiled;
+            // Exactly-once latch for the pull above. Armed with every new job node, set by
+            // the one join that consumes it.
+            mutable Bool m_compileJoined = false;
         };
     } // namespace MG_State::GLState
 } // namespace MobileGL

MobileGL/MG_State/GLState/ProgramState/ShaderPreprocessCache.h

@@ -10,7 +10,9 @@
 #include <Includes.h>
 #include <list>
 #include <mutex>
-#include <MG_State/GLState/ProgramState/ShaderObject.h>
+// Deliberately NOT ShaderObject.h: ShaderCompileTask.h needs this header, and ShaderObject.h
+// needs ShaderCompileTask.h. Only ShaderStage was ever used from there.
+#include <MG_State/GLState/ProgramState/ShaderStage.h>
 
 namespace MobileGL::MG_State::GLState {
     // Where the shared, source-only half of ShaderObject::Compile() stopped. The two

MobileGL/MG_State/GLState/ProgramState/ShaderStage.h

@@ -0,0 +1,25 @@
+// MobileGL - MobileGL/MG_State/GLState/ProgramState/ShaderStage.h
+// Copyright (c) 2025-2026 MobileGL-Dev
+// Licensed under the GNU Lesser General Public License v3.0:
+//   https://www.gnu.org/licenses/gpl-3.0.txt
+//   https://www.gnu.org/licenses/lgpl-3.0.txt
+// SPDX-License-Identifier: LGPL-3.0-only
+// End of Source File Header
+
+#pragma once
+
+namespace MobileGL {
+    // Split out of ShaderObject.h so the compile pipeline's headers form a DAG:
+    // ShaderStage.h <- ShaderPreprocessCache.h <- ShaderCompileTask.h <- ShaderObject.h.
+    // Every existing includer of ShaderObject.h still sees this type unchanged.
+    enum class ShaderStage {
+        Vertex,
+        TessControl,
+        TessEval,
+        Geometry,
+        Fragment,
+        Compute,
+        ShaderStageCount,
+        Unknown = -1
+    };
+} // namespace MobileGL

MobileGL/MG_Test/Program/AsyncCompileTest.cpp

@@ -0,0 +1,571 @@
+// MobileGL - MobileGL/MG_Test/Program/AsyncCompileTest.cpp
+// Copyright (c) 2025-2026 MobileGL-Dev
+// Licensed under the GNU Lesser General Public License v3.0:
+//   https://www.gnu.org/licenses/gpl-3.0.txt
+//   https://www.gnu.org/licenses/lgpl-3.0.txt
+// SPDX-License-Identifier: LGPL-3.0-only
+// End of Source File Header
+
+// P1 stage 3: glCompileShader enqueues, and every observable read joins.
+//
+// Every test here drives the real GL entry points and flips
+// MG_Config::Features.AsyncShaderCompile itself rather than reading the environment. That is
+// what lets one binary assert the property that actually matters - the async path and the
+// synchronous path are indistinguishable through the GL surface - and it makes the file
+// behave identically whether or not the suite was launched with
+// MOBILEGL_ASYNC_SHADER_COMPILE=1.
+
+#include <gtest/gtest.h>
+
+#include <chrono>
+#include <string>
+#include <vector>
+
+#include "Config.h"
+#include "Includes.h"
+#include "Init.h"
+#include "MG_Impl/GLImpl/Getter/GL_Getter.h"
+#include "MG_Impl/GLImpl/Program/GL_Program.h"
+#include "MG_State/GLState/Core.h"
+#include "MG_Util/Async/ShaderCompilePool.h"
+
+using namespace MobileGL;
+using namespace MobileGL::MG_Impl::GLImpl;
+
+namespace {
+    // Restores whatever the environment asked for when the test ends, so a case that forces
+    // one mode cannot leak into the next.
+    class AsyncModeScope {
+    public:
+        explicit AsyncModeScope(const Bool async)
+            : m_saved(MG_Config::Features.AsyncShaderCompile) {
+            MG_Config::Features.AsyncShaderCompile =
+                async ? MG_Config::QuirkOverride::ForceOn : MG_Config::QuirkOverride::ForceOff;
+        }
+        ~AsyncModeScope() { MG_Config::Features.AsyncShaderCompile = m_saved; }
+        AsyncModeScope(const AsyncModeScope&) = delete;
+        AsyncModeScope& operator=(const AsyncModeScope&) = delete;
+
+    private:
+        const MG_Config::QuirkOverride m_saved;
+    };
+
+    const char* kVs = R"(#version 460
+layout(location = 0) in vec3 aPos;
+uniform mat4 uModel;
+uniform vec4 uColor;
+out vec4 vColor;
+void main() {
+    vColor = uColor;
+    gl_Position = uModel * vec4(aPos, 1.0);
+}
+)";
+
+    const char* kFs = R"(#version 460
+in vec4 vColor;
+layout(location = 0) out vec4 fragColor;
+uniform float uAlpha;
+void main() { fragColor = vec4(vColor.rgb, vColor.a * uAlpha); }
+)";
+
+    // Fails in glslang, not in the lexical pre-checks: that routes through the same
+    // ParseFailed path a real broken shaderpack source takes.
+    const char* kBrokenFs = R"(#version 460
+layout(location = 0) out vec4 fragColor;
+void main() { fragColor = thisIdentifierWasNeverDeclared; }
+)";
+
+    // Rejected by the lexical reserved-identifier scan, before glslang is ever reached - the
+    // other half of the "compile failed" surface, and the one that never allocates a parse.
+    const char* kReservedIdentifierFs = R"(#version 460
+layout(location = 0) out vec4 fragColor;
+float gl_NotAllowedToDeclareThis = 1.0;
+void main() { fragColor = vec4(gl_NotAllowedToDeclareThis); }
+)";
+
+    // Big enough that a compile is not instantaneous, so the pool actually has a backlog to
+    // observe. Templated on an index so every instance is a distinct source (no P0b hit).
+    String MakeBulkySource(const int index) {
+        String source = "#version 460\nlayout(location = 0) out vec4 fragColor;\n";
+        source += "uniform float uSeed" + std::to_string(index) + ";\n";
+        source += "void main() {\n    float acc = uSeed" + std::to_string(index) + ";\n";
+        for (int i = 0; i < 220; ++i) {
+            source += "    acc = acc * 1.0001 + sin(acc + " + std::to_string(i) + ".0) * cos(acc);\n";
+        }
+        source += "    fragColor = vec4(acc, acc, acc, 1.0);\n}\n";
+        return source;
+    }
+
+    GLuint MakeShader(const GLenum type, const char* source) {
+        const GLuint shader = CreateShader(type);
+        ShaderSource(shader, 1, &source, nullptr);
+        return shader;
+    }
+
+    GLint QueryCompileStatus(const GLuint shader) {
+        GLint status = GL_FALSE;
+        GetShaderiv(shader, GL_COMPILE_STATUS, &status);
+        return status;
+    }
+
+    String QueryShaderInfoLog(const GLuint shader) {
+        GLint length = 0;
+        GetShaderiv(shader, GL_INFO_LOG_LENGTH, &length);
+        if (length <= 0) return String();
+        std::vector<GLchar> buffer(static_cast<size_t>(length));
+        GLsizei written = 0;
+        GetShaderInfoLog(shader, length, &written, buffer.data());
+        return String(buffer.data(), static_cast<size_t>(written));
+    }
+
+    GLint QueryLinkStatus(const GLuint program) {
+        GLint status = GL_FALSE;
+        GetProgramiv(program, GL_LINK_STATUS, &status);
+        return status;
+    }
+
+    // The non-joining view of the object, i.e. what GL_COMPLETION_STATUS_KHR will report.
+    Bool CompileIsSettled(const GLuint shader) {
+        const auto& object = MG_State::pGLContext->GetShaderObject(shader);
+        return object == nullptr || object->IsCompileComplete();
+    }
+
+    Bool HasMemoizedCompile(const GLuint shader) {
+        const auto& object = MG_State::pGLContext->GetShaderObject(shader);
+        return object != nullptr && object->HasMemoizedCompile();
+    }
+
+    // Enqueues `count` distinct heavy compiles and returns their names WITHOUT reading
+    // anything back, so the pool is left with a real backlog for the caller to race against.
+    Vector<GLuint> SaturatePool(const int count, Vector<String>& sourceStorage) {
+        Vector<GLuint> shaders;
+        shaders.reserve(static_cast<SizeT>(count));
+        sourceStorage.reserve(sourceStorage.size() + static_cast<SizeT>(count));
+        for (int i = 0; i < count; ++i) {
+            sourceStorage.push_back(MakeBulkySource(1000 + i));
+            const char* text = sourceStorage.back().c_str();
+            const GLuint shader = CreateShader(GL_FRAGMENT_SHADER);
+            ShaderSource(shader, 1, &text, nullptr);
+            CompileShader(shader);
+            shaders.push_back(shader);
+        }
+        return shaders;
+    }
+
+    class AsyncCompileTest : public ::testing::Test {
+    protected:
+        void SetUp() override { MobileGL::Initialize(); }
+    };
+} // namespace
+
+// ---------------------------------------------------------------------------------------
+// Correctness through the full GL surface
+// ---------------------------------------------------------------------------------------
+
+// N shaders compiled with the flag on: every status, every info log and every link has to
+// come out the same as the synchronous path produces.
+TEST_F(AsyncCompileTest, ManyShadersCompileAndLinkCorrectlyWithAsyncOn) {
+    const AsyncModeScope async(true);
+    ASSERT_TRUE(MG_Util::Async::AsyncShaderCompileEnabled());
+
+    constexpr int kCount = 24;
+    Vector<GLuint> vertexShaders;
+    Vector<GLuint> fragmentShaders;
+    Vector<String> sources;
+    sources.reserve(kCount);
+
+    // Enqueue everything first, read nothing: this is the shape a shaderpack load has, and
+    // the only shape where the pool has more than one job in flight at a time.
+    for (int i = 0; i < kCount; ++i) {
+        vertexShaders.push_back(MakeShader(GL_VERTEX_SHADER, kVs));
+        sources.push_back(MakeBulkySource(i));
+        const char* text = sources.back().c_str();
+        const GLuint fs = CreateShader(GL_FRAGMENT_SHADER);
+        ShaderSource(fs, 1, &text, nullptr);
+        CompileShader(fs);
+        fragmentShaders.push_back(fs);
+        CompileShader(vertexShaders.back());
+    }
+
+    for (int i = 0; i < kCount; ++i) {
+        EXPECT_EQ(QueryCompileStatus(vertexShaders[i]), GL_TRUE) << QueryShaderInfoLog(vertexShaders[i]);
+        EXPECT_EQ(QueryCompileStatus(fragmentShaders[i]), GL_TRUE) << QueryShaderInfoLog(fragmentShaders[i]);
+        EXPECT_TRUE(QueryShaderInfoLog(vertexShaders[i]).empty());
+        EXPECT_TRUE(QueryShaderInfoLog(fragmentShaders[i]).empty());
+    }
+
+    // And the artifacts are actually usable: link, and reflect a uniform out of each stage.
+    for (int i = 0; i < kCount; ++i) {
+        const GLuint program = CreateProgram();
+        AttachShader(program, vertexShaders[i]);
+        AttachShader(program, fragmentShaders[i]);
+        LinkProgram(program);
+        ASSERT_EQ(QueryLinkStatus(program), GL_TRUE) << "program " << i;
+        EXPECT_GE(GetUniformLocation(program, "uColor"), 0);
+        EXPECT_GE(GetUniformLocation(program, ("uSeed" + std::to_string(i)).c_str()), 0);
+    }
+    EXPECT_EQ(GetError(), GL_NO_ERROR);
+}
+
+// glCompileShader must return before the work is done. Timing-based assertions flake, so
+// this observes the state machine instead: with a saturated pool at least one of the just
+// -enqueued shaders has to be unsettled at the moment we ask. Skipped rather than failed if
+// the machine drained the whole batch first - it can then never be a false red.
+TEST_F(AsyncCompileTest, CompileShaderReturnsBeforeTheWorkIsDone) {
+    const AsyncModeScope async(true);
+    Vector<String> sources;
+    const Vector<GLuint> shaders = SaturatePool(64, sources);
+
+    int unsettled = 0;
+    for (const GLuint shader : shaders) {
+        if (!CompileIsSettled(shader)) ++unsettled;
+    }
+    if (unsettled == 0) {
+        GTEST_SKIP() << "the pool drained 64 compiles before the first observation; nothing to prove here";
+    }
+
+    // Whatever was outstanding still has to produce the right answer once asked.
+    for (const GLuint shader : shaders) {
+        EXPECT_EQ(QueryCompileStatus(shader), GL_TRUE) << QueryShaderInfoLog(shader);
+        EXPECT_TRUE(CompileIsSettled(shader)) << "reading COMPILE_STATUS must have joined";
+    }
+    EXPECT_EQ(GetError(), GL_NO_ERROR);
+}
+
+// The synchronous path must stay synchronous: with the flag off, a compile is finished by
+// the time glCompileShader returns. This is the guard that keeps the default shippable.
+TEST_F(AsyncCompileTest, CompileIsFullySynchronousWithAsyncOff) {
+    const AsyncModeScope async(false);
+    ASSERT_FALSE(MG_Util::Async::AsyncShaderCompileEnabled());
+
+    Vector<String> sources;
+    const Vector<GLuint> shaders = SaturatePool(8, sources);
+    for (const GLuint shader : shaders) {
+        EXPECT_TRUE(CompileIsSettled(shader));
+        EXPECT_TRUE(HasMemoizedCompile(shader));
+        EXPECT_EQ(QueryCompileStatus(shader), GL_TRUE) << QueryShaderInfoLog(shader);
+    }
+    EXPECT_EQ(GetError(), GL_NO_ERROR);
+}
+
+// ---------------------------------------------------------------------------------------
+// Diagnostics: the failing paths must read identically in both modes
+// ---------------------------------------------------------------------------------------
+
+// A compile failure is reported through COMPILE_STATUS and the info log, never through
+// glGetError - that is exactly why moving the work off-thread is legal. Both failure
+// classes are covered: the glslang parse failure and the lexical reserved-identifier
+// rejection (which never reaches glslang at all).
+TEST_F(AsyncCompileTest, FailingCompileLogIsByteIdenticalAcrossModes) {
+    for (const char* source : {kBrokenFs, kReservedIdentifierFs}) {
+        String syncLog;
+        {
+            const AsyncModeScope async(false);
+            const GLuint fs = MakeShader(GL_FRAGMENT_SHADER, source);
+            CompileShader(fs);
+            ASSERT_EQ(QueryCompileStatus(fs), GL_FALSE);
+            syncLog = QueryShaderInfoLog(fs);
+            EXPECT_FALSE(syncLog.empty());
+            // GL defines compile FAILURE as a status plus a log, not as a GL error.
+            EXPECT_EQ(GetError(), GL_NO_ERROR);
+        }
+        {
+            const AsyncModeScope async(true);
+            const GLuint fs = MakeShader(GL_FRAGMENT_SHADER, source);
+            CompileShader(fs);
+            EXPECT_EQ(QueryCompileStatus(fs), GL_FALSE);
+            EXPECT_EQ(QueryShaderInfoLog(fs), syncLog);
+            EXPECT_EQ(GetError(), GL_NO_ERROR);
+        }
+    }
+}
+
+// A link whose vertex shader failed to compile has to reproduce that shader's log verbatim
+// inside the program info log, whichever thread produced it.
+TEST_F(AsyncCompileTest, LinkDiagnosticsQuoteTheAsyncCompileLog) {
+    const AsyncModeScope async(true);
+    const GLuint vs = MakeShader(GL_VERTEX_SHADER, kVs);
+    const GLuint fs = MakeShader(GL_FRAGMENT_SHADER, kBrokenFs);
+    CompileShader(vs);
+    CompileShader(fs);
+
+    const GLuint program = CreateProgram();
+    AttachShader(program, vs);
+    AttachShader(program, fs);
+    // No status read between the enqueue and the link: the link's own prologue is what has
+    // to join the two compiles.
+    LinkProgram(program);
+    EXPECT_EQ(QueryLinkStatus(program), GL_FALSE);
+
+    GLint length = 0;
+    GetProgramiv(program, GL_INFO_LOG_LENGTH, &length);
+    ASSERT_GT(length, 1);
+    std::vector<GLchar> buffer(static_cast<size_t>(length));
+    GLsizei written = 0;
+    GetProgramInfoLog(program, length, &written, buffer.data());
+    const String programLog(buffer.data(), static_cast<size_t>(written));
+    const String shaderLog = QueryShaderInfoLog(fs);
+    ASSERT_FALSE(shaderLog.empty());
+    EXPECT_NE(programLog.find(shaderLog), String::npos)
+        << "program log:\n" << programLog << "\nshader log:\n" << shaderLog;
+    EXPECT_EQ(GetError(), GL_NO_ERROR);
+}
+
+// ---------------------------------------------------------------------------------------
+// Mutation over an in-flight compile
+// ---------------------------------------------------------------------------------------
+
+// glShaderSource with DIFFERENT text over a pending compile: the running job is abandoned
+// and the next compile reflects the new source. The re-source happens with the pool
+// saturated, so the job it replaces is very likely still queued or running.
+TEST_F(AsyncCompileTest, ShaderSourceOverAPendingCompileCancelsAndTheNewSourceWins) {
+    const AsyncModeScope async(true);
+    Vector<String> backlog;
+    SaturatePool(48, backlog);
+
+    const String firstSource = MakeBulkySource(7001);
+    const char* firstText = firstSource.c_str();
+    const GLuint fs = CreateShader(GL_FRAGMENT_SHADER);
+    ShaderSource(fs, 1, &firstText, nullptr);
+    CompileShader(fs);
+
+    // Replace the text while that compile is (very probably) still outstanding. This must
+    // not wait, must not corrupt the abandoned job's view of the old string, and must
+    // disarm the layer-1 memo.
+    const String secondSource = MakeBulkySource(7002);
+    const char* secondText = secondSource.c_str();
+    ShaderSource(fs, 1, &secondText, nullptr);
+    EXPECT_FALSE(HasMemoizedCompile(fs)) << "a real source change must invalidate the compiled state";
+    EXPECT_EQ(QueryCompileStatus(fs), GL_FALSE) << "the replaced compile must not publish";
+
+    CompileShader(fs);
+    ASSERT_EQ(QueryCompileStatus(fs), GL_TRUE) << QueryShaderInfoLog(fs);
+
+    const GLuint vs = MakeShader(GL_VERTEX_SHADER, kVs);
+    CompileShader(vs);
+    const GLuint program = CreateProgram();
+    AttachShader(program, vs);
+    AttachShader(program, fs);
+    LinkProgram(program);
+    ASSERT_EQ(QueryLinkStatus(program), GL_TRUE);
+    // The SECOND source's uniform is the one that exists.
+    EXPECT_GE(GetUniformLocation(program, "uSeed7002"), 0);
+    EXPECT_EQ(GetUniformLocation(program, "uSeed7001"), -1);
+    EXPECT_EQ(GetError(), GL_NO_ERROR);
+}
+
+// glShaderSource with byte-identical text over a pending compile is a no-op: the job stays,
+// the memo stays armed, and the result is still the right one.
+TEST_F(AsyncCompileTest, IdenticalShaderSourceOverAPendingCompileKeepsTheJob) {
+    const AsyncModeScope async(true);
+    Vector<String> backlog;
+    SaturatePool(48, backlog);
+
+    const String source = MakeBulkySource(7100);
+    const char* text = source.c_str();
+    const GLuint fs = CreateShader(GL_FRAGMENT_SHADER);
+    ShaderSource(fs, 1, &text, nullptr);
+    CompileShader(fs);
+
+    ShaderSource(fs, 1, &text, nullptr);
+    EXPECT_TRUE(HasMemoizedCompile(fs)) << "identical re-source must not disturb an in-flight compile";
+    EXPECT_EQ(QueryCompileStatus(fs), GL_TRUE) << QueryShaderInfoLog(fs);
+    EXPECT_EQ(GetError(), GL_NO_ERROR);
+}
+
+// A second glCompileShader on a pending object must be a no-op, not a duplicate job racing
+// the first one to write the same fields. Observed through the object identity of the node:
+// HasMemoizedCompile stays true across the second call, and the result is still correct.
+TEST_F(AsyncCompileTest, RepeatedCompileShaderOnAPendingObjectEnqueuesOneJob) {
+    const AsyncModeScope async(true);
+    Vector<String> backlog;
+    SaturatePool(48, backlog);
+
+    const String source = MakeBulkySource(7200);
+    const char* text = source.c_str();
+    const GLuint fs = CreateShader(GL_FRAGMENT_SHADER);
+    ShaderSource(fs, 1, &text, nullptr);
+
+    // A copy, not the slot reference: creating another shader can reallocate the table.
+    const SharedPtr<MG_State::GLState::ShaderObject> object = MG_State::pGLContext->GetShaderObject(fs);
+    ASSERT_NE(object, nullptr);
+    EXPECT_FALSE(object->HasMemoizedCompile());
+    CompileShader(fs);
+    EXPECT_TRUE(object->HasMemoizedCompile());
+    for (int i = 0; i < 8; ++i) {
+        CompileShader(fs);
+        EXPECT_TRUE(object->HasMemoizedCompile());
+    }
+
+    EXPECT_EQ(QueryCompileStatus(fs), GL_TRUE) << QueryShaderInfoLog(fs);
+    EXPECT_EQ(GetError(), GL_NO_ERROR);
+}
+
+// glDeleteShader on an unattached object with a compile still in flight. The name goes away
+// immediately - no wait for a worker - and the abandoned job must neither crash nor keep the
+// object alive in a way anything can observe.
+TEST_F(AsyncCompileTest, DeleteShaderWhileACompileIsPending) {
+    const AsyncModeScope async(true);
+    Vector<String> backlog;
+    SaturatePool(48, backlog);
+
+    Vector<GLuint> doomed;
+    Vector<String> sources;
+    for (int i = 0; i < 16; ++i) {
+        sources.push_back(MakeBulkySource(7300 + i));
+        const char* text = sources.back().c_str();
+        const GLuint fs = CreateShader(GL_FRAGMENT_SHADER);
+        ShaderSource(fs, 1, &text, nullptr);
+        CompileShader(fs);
+        doomed.push_back(fs);
+    }
+    for (const GLuint fs : doomed) {
+        DeleteShader(fs);
+        EXPECT_EQ(IsShader(fs), GL_FALSE) << "an unattached deleted shader's name goes immediately";
+    }
+    EXPECT_EQ(GetError(), GL_NO_ERROR);
+
+    // The context still works afterwards - the abandoned jobs did not take the pool, the
+    // preprocess cache or the glslang process state down with them.
+    const GLuint vs = MakeShader(GL_VERTEX_SHADER, kVs);
+    const GLuint fs = MakeShader(GL_FRAGMENT_SHADER, kFs);
+    CompileShader(vs);
+    CompileShader(fs);
+    const GLuint program = CreateProgram();
+    AttachShader(program, vs);
+    AttachShader(program, fs);
+    LinkProgram(program);
+    EXPECT_EQ(QueryLinkStatus(program), GL_TRUE);
+    EXPECT_EQ(GetError(), GL_NO_ERROR);
+}
+
+// glDeleteShader on a shader still ATTACHED to a program only flags it: the pending compile
+// has to survive, because the link that follows still needs its artifacts.
+TEST_F(AsyncCompileTest, DeleteShaderWhileAttachedKeepsThePendingCompileAlive) {
+    const AsyncModeScope async(true);
+    Vector<String> backlog;
+    SaturatePool(48, backlog);
+
+    const GLuint vs = MakeShader(GL_VERTEX_SHADER, kVs);
+    const GLuint fs = MakeShader(GL_FRAGMENT_SHADER, kFs);
+    const GLuint program = CreateProgram();
+    AttachShader(program, vs);
+    AttachShader(program, fs);
+    CompileShader(vs);
+    CompileShader(fs);
+    DeleteShader(vs);
+    DeleteShader(fs);
+
+    LinkProgram(program);
+    ASSERT_EQ(QueryLinkStatus(program), GL_TRUE);
+    EXPECT_GE(GetUniformLocation(program, "uColor"), 0);
+    EXPECT_GE(GetUniformLocation(program, "uAlpha"), 0);
+    EXPECT_EQ(GetError(), GL_NO_ERROR);
+}
+
+// ---------------------------------------------------------------------------------------
+// Stress
+// ---------------------------------------------------------------------------------------
+
+// The adversarial interleaving: enqueue, query, re-source, re-enqueue, delete, all with the
+// pool busy. Nothing here asserts timing - what it hunts for is a missed join or a use of an
+// abandoned node, both of which surface as a wrong status, a wrong log, or a crash.
+TEST_F(AsyncCompileTest, StressCompileQueryResourceDeleteInterleaved) {
+    const AsyncModeScope async(true);
+    constexpr int kRounds = 6;
+    constexpr int kPerRound = 12;
+
+    for (int round = 0; round < kRounds; ++round) {
+        Vector<String> sources;
+        Vector<GLuint> shaders;
+        sources.reserve(kPerRound * 2);
+
+        for (int i = 0; i < kPerRound; ++i) {
+            sources.push_back(MakeBulkySource(round * 1000 + i));
+            const char* text = sources.back().c_str();
+            const GLuint fs = CreateShader(GL_FRAGMENT_SHADER);
+            ShaderSource(fs, 1, &text, nullptr);
+            CompileShader(fs);
+            shaders.push_back(fs);
+
+            // Immediately query a PREVIOUS one while this one is still outstanding: the
+            // join has to settle exactly the object asked about and no other.
+            if (i > 0) {
+                const GLuint earlier = shaders[static_cast<SizeT>(i - 1)];
+                EXPECT_EQ(QueryCompileStatus(earlier), GL_TRUE) << QueryShaderInfoLog(earlier);
+            }
+        }
+
+        // Re-source half of them mid-flight, then recompile.
+        for (int i = 0; i < kPerRound; i += 2) {
+            sources.push_back(MakeBulkySource(round * 1000 + 500 + i));
+            const char* text = sources.back().c_str();
+            ShaderSource(shaders[static_cast<SizeT>(i)], 1, &text, nullptr);
+            CompileShader(shaders[static_cast<SizeT>(i)]);
+        }
+
+        for (int i = 0; i < kPerRound; ++i) {
+            const GLuint shader = shaders[static_cast<SizeT>(i)];
+            EXPECT_EQ(QueryCompileStatus(shader), GL_TRUE) << QueryShaderInfoLog(shader);
+            const String expectedUniform =
+                "uSeed" + std::to_string(round * 1000 + (i % 2 == 0 ? 500 + i : i));
+            const GLuint vs = MakeShader(GL_VERTEX_SHADER, kVs);
+            CompileShader(vs);
+            const GLuint program = CreateProgram();
+            AttachShader(program, vs);
+            AttachShader(program, shader);
+            LinkProgram(program);
+            ASSERT_EQ(QueryLinkStatus(program), GL_TRUE) << "round " << round << " shader " << i;
+            EXPECT_GE(GetUniformLocation(program, expectedUniform.c_str()), 0)
+                << "round " << round << " shader " << i << " expected " << expectedUniform;
+            DeleteProgram(program);
+            DeleteShader(vs);
+        }
+        for (const GLuint shader : shaders) {
+            DeleteShader(shader);
+        }
+        EXPECT_EQ(GetError(), GL_NO_ERROR);
+    }
+}
+
+// The P0b cross-object memo is hit from several workers at once here: 8 objects share each
+// of 6 distinct sources, all enqueued before anything is read. Every object must still end
+// up with its own parse and its own correct reflection - a torn cache entry or an entry
+// evicted from under a reader shows up as a link failure or a missing uniform.
+TEST_F(AsyncCompileTest, ConcurrentCompilesShareThePreprocessCacheSafely) {
+    const AsyncModeScope async(true);
+    constexpr int kDistinct = 6;
+    constexpr int kDuplicates = 8;
+
+    Vector<String> sources;
+    sources.reserve(kDistinct);
+    for (int i = 0; i < kDistinct; ++i) {
+        sources.push_back(MakeBulkySource(8100 + i));
+    }
+
+    Vector<GLuint> shaders;
+    for (int duplicate = 0; duplicate < kDuplicates; ++duplicate) {
+        for (int i = 0; i < kDistinct; ++i) {
+            const char* text = sources[static_cast<SizeT>(i)].c_str();
+            const GLuint fs = CreateShader(GL_FRAGMENT_SHADER);
+            ShaderSource(fs, 1, &text, nullptr);
+            CompileShader(fs);
+            shaders.push_back(fs);
+        }
+    }
+
+    for (SizeT s = 0; s < shaders.size(); ++s) {
+        const GLuint fs = shaders[s];
+        ASSERT_EQ(QueryCompileStatus(fs), GL_TRUE) << QueryShaderInfoLog(fs);
+        const GLuint vs = MakeShader(GL_VERTEX_SHADER, kVs);
+        CompileShader(vs);
+        const GLuint program = CreateProgram();
+        AttachShader(program, vs);
+        AttachShader(program, fs);
+        LinkProgram(program);
+        ASSERT_EQ(QueryLinkStatus(program), GL_TRUE) << "shader index " << s;
+        const String uniform = "uSeed" + std::to_string(8100 + static_cast<int>(s % kDistinct));
+        EXPECT_GE(GetUniformLocation(program, uniform.c_str()), 0) << uniform;
+    }
+    EXPECT_EQ(GetError(), GL_NO_ERROR);
+}

MobileGL/MG_Test/Program/CMakeLists.txt

@@ -28,6 +28,22 @@ add_executable(
         ProgramTest.cpp
 )
 
+add_executable(
+        AsyncCompileTest
+        AsyncCompileTest.cpp
+)
+
+target_include_directories(AsyncCompileTest PRIVATE
+        ${MGL_ROOT}/include
+        ${MGL_ROOT}/MobileGL
+)
+
+target_link_libraries(
+        AsyncCompileTest PRIVATE
+        GTest::gtest_main
+        ${LINK_LIBRARIES}
+)
+
 target_include_directories(ProgramTest PRIVATE
         ${MGL_ROOT}/include
         ${MGL_ROOT}/MobileGL
@@ -42,3 +58,6 @@ target_link_libraries(
 include(GoogleTest)
 gtest_discover_tests(ProgramUtilTest DISCOVERY_TIMEOUT 30 PROPERTIES LABELS unit)
 gtest_discover_tests(ProgramTest DISCOVERY_TIMEOUT 30 PROPERTIES LABELS unit)
+# Heavier than the rest of the unit suite by design: several cases deliberately saturate the
+# compile pool so there is something in flight to race against.
+gtest_discover_tests(AsyncCompileTest DISCOVERY_TIMEOUT 60 PROPERTIES LABELS unit TIMEOUT 300)

MobileGL/MG_Test/Util/JobNodeTest.cpp

@@ -135,12 +135,25 @@ TEST(ShaderCompilePoolLifecycle, DetectedThreadCountIsPositive) {
     EXPECT_GE(DetectShaderCompileThreadCount(), 1u);
 }
 
-TEST(ShaderCompilePoolLifecycle, AsyncIsOffByDefaultInThisStage) {
-    // Stage 1 ships the machinery wired to nothing. If this ever fails without the default
-    // constant having been deliberately flipped, something enabled async by accident.
-    EXPECT_EQ(MG_Config::Features.AsyncShaderCompile, MG_Config::QuirkOverride::Auto);
+TEST(ShaderCompilePoolLifecycle, AsyncIsOffByDefaultAndTheOverrideDecidesEitherWay) {
+    // The shipped default is still off, and an unset MOBILEGL_ASYNC_SHADER_COMPILE resolves
+    // to it. If the first expectation ever fails without the constant having been
+    // deliberately flipped, something enabled async by accident.
+    //
+    // Driven through Features rather than read from it: from stage 3 on, the whole suite is
+    // also run with MOBILEGL_ASYNC_SHADER_COMPILE=1 exported, so a test that simply asserted
+    // "the resolved answer is false" would either fail there or - worse - silently pass in a
+    // binary that never loaded the config and prove nothing at all.
     EXPECT_FALSE(kAsyncShaderCompileDefault);
+
+    const MG_Config::QuirkOverride saved = MG_Config::Features.AsyncShaderCompile;
+    MG_Config::Features.AsyncShaderCompile = MG_Config::QuirkOverride::Auto;
+    EXPECT_EQ(AsyncShaderCompileEnabled(), kAsyncShaderCompileDefault);
+    MG_Config::Features.AsyncShaderCompile = MG_Config::QuirkOverride::ForceOn;
+    EXPECT_TRUE(AsyncShaderCompileEnabled());
+    MG_Config::Features.AsyncShaderCompile = MG_Config::QuirkOverride::ForceOff;
     EXPECT_FALSE(AsyncShaderCompileEnabled());
+    MG_Config::Features.AsyncShaderCompile = saved;
 }
 
 // ---------------------------------------------------------------------------------------

MobileGL/MG_Util/Async/JobNode.cpp

@@ -9,6 +9,8 @@
 #include "JobNode.h"
 #include "ShaderCompilePool.h"
 
+#include <MG_State/GLState/Core.h>
+
 namespace MobileGL::MG_Util::Async {
     namespace {
         Bool IsTerminalState(const JobState state) {
@@ -122,4 +124,35 @@ namespace MobileGL::MG_Util::Async {
         }
         fn();
     }
+
+    void ApplyDeferredDiagnostics(JobNode& node) {
+        MOBILEGL_ASSERT(!ShaderCompilePool::IsPoolThread(),
+                        "ApplyDeferredDiagnostics() called from a pool thread; deferred diagnostics exist precisely "
+                        "so that a worker never touches the GL error state");
+        MOBILEGL_ASSERT(node.IsTerminal(),
+                        "ApplyDeferredDiagnostics() called on a job that has not settled; its diagnostics are still "
+                        "being written");
+
+        if (!node.diagnostics.logLines.empty()) {
+            Vector<String> lines;
+            lines.swap(node.diagnostics.logLines);
+            for (const String& line : lines) {
+                MGLOG_W("%s", line.c_str());
+            }
+        }
+
+        if (node.diagnostics.errors.empty()) return;
+        Vector<DeferredError> errors;
+        errors.swap(node.diagnostics.errors);
+        // Ascending sequence == job-enqueue order == the order a serial implementation would
+        // have recorded them in, which is what decides WHICH payload the application sees:
+        // MobileGL implements GL's sticky-flag semantics, so a repeat of an already-pending
+        // code is discarded and only the first occurrence of each code survives.
+        std::sort(errors.begin(), errors.end(),
+                  [](const DeferredError& a, const DeferredError& b) { return a.sequence < b.sequence; });
+        if (!MG_State::pGLContext) return;
+        for (DeferredError& error : errors) {
+            MG_State::pGLContext->RecordError(error.code, Move(error.info));
+        }
+    }
 } // namespace MobileGL::MG_Util::Async

MobileGL/MG_Util/Async/JobNode.h

@@ -113,4 +113,15 @@ namespace MobileGL::MG_Util::Async {
         std::atomic<Bool> m_cancelled{false};
         Vector<std::function<void()>> m_continuations;
     };
+
+    // Replays a settled node's worker-side diagnostics on the calling thread: log lines
+    // first, in the order the body produced them, then any deferred GL error in ascending
+    // `sequence`. GL thread only - it is the join that calls this, which is exactly the
+    // point at which a deferred error becomes indistinguishable from one a serial
+    // implementation would have raised inside glCompileShader/glLinkProgram (an application
+    // cannot observe a pending job's effects by any other route).
+    //
+    // Drains what it replays, so calling it twice on one node is a no-op the second time.
+    // Must be called with the node terminal.
+    void ApplyDeferredDiagnostics(JobNode& node);
 } // namespace MobileGL::MG_Util::Async

MobileGL/MG_Util/Async/ShaderCompilePool.cpp

@@ -36,11 +36,29 @@ namespace MobileGL::MG_Util::Async {
         // first pool use, so it is guaranteed to run before any static destructor.
         Bool g_processTeardown = false;
         std::once_flag g_teardownSentinelOnce;
+        // The process-wide pool from Get(), for the atexit handler to stop. Never the
+        // stack-allocated pools a test builds - those join themselves in their destructor.
+        std::atomic<ShaderCompilePool*> g_processPool{nullptr};
 
         Bool InProcessTeardown() { return g_processTeardown; }
 
         void EnsureProcessTeardownSentinel() {
-            std::call_once(g_teardownSentinelOnce, [] { std::atexit(+[] { g_processTeardown = true; }); });
+            std::call_once(g_teardownSentinelOnce, [] {
+                std::atexit(+[] {
+                    g_processTeardown = true;
+                    // Latching the flag is not enough: a worker that is ALREADY inside
+                    // glslang has to be out of it before static destruction reaches
+                    // glslang's process globals, the SPIRV-Tools tables, or anything else a
+                    // job body touches. This is the same wait Init.cpp's DestroyImpl does -
+                    // it just also has to happen for a process that exits without ever
+                    // calling eglTerminate, which is the norm for a test binary and legal
+                    // for an application. Registered here, during main, so it runs before
+                    // the destructors of statics constructed at load time.
+                    if (ShaderCompilePool* pool = g_processPool.load(std::memory_order_acquire)) {
+                        pool->StopAndDrain();
+                    }
+                });
+            });
         }
 
         Uint64 ReadCpuMaxFrequencyKHz(const Uint cpu) {
@@ -120,10 +138,20 @@ namespace MobileGL::MG_Util::Async {
         // re-enter this mutex.
         void DispatchLocked() {
             while (!queue.empty() && inFlight < maxConcurrency && !stopped.load(std::memory_order_acquire)) {
-                SharedPtr<JobNode> node = Move(queue.front());
+                // Copy rather than move into the handler: if asio::post throws (it allocates)
+                // the local SharedPtr is still valid, so the node can be settled instead of
+                // being stranded Pending in a queue nothing will dispatch from again - a
+                // joiner would block on it forever. Reclaiming the slot matters just as much:
+                // a leaked `inFlight` shrinks the pool's concurrency budget permanently.
+                SharedPtr<JobNode> node = queue.front();
                 queue.pop_front();
                 ++inFlight;
-                asio::post(*pool, [this, node = Move(node)]() mutable { RunOnWorker(Move(node)); });
+                try {
+                    asio::post(*pool, [this, node]() mutable { RunOnWorker(Move(node)); });
+                } catch (...) {
+                    --inFlight;
+                    node->Cancel();
+                }
             }
         }
 
@@ -147,10 +175,17 @@ namespace MobileGL::MG_Util::Async {
     ShaderCompilePool::~ShaderCompilePool() { StopAndDrain(); }
 
     ShaderCompilePool& ShaderCompilePool::Get() {
-        // Leak-at-exit, like the other MobileGL singletons: a process that exits without
-        // eglTerminate hands the threads to the OS rather than joining them from a static
-        // destructor, where the rest of the library may already be gone.
-        static ShaderCompilePool* pool = new ShaderCompilePool(DetectShaderCompileThreadCount());
+        // Leak-at-exit, like the other MobileGL singletons: the object itself is never
+        // destroyed, so no static destructor can race a late entry point for it. Its THREADS
+        // are a different matter and are stopped explicitly - by Init.cpp's DestroyImpl on
+        // the normal path, and by the atexit sentinel below for a process that exits without
+        // ever calling eglTerminate.
+        static ShaderCompilePool* pool = [] {
+            auto* created = new ShaderCompilePool(DetectShaderCompileThreadCount());
+            g_processPool.store(created, std::memory_order_release);
+            EnsureProcessTeardownSentinel();
+            return created;
+        }();
         return *pool;
     }
 
@@ -174,7 +209,18 @@ namespace MobileGL::MG_Util::Async {
         if (!node) return;
         EnsureProcessTeardownSentinel();
 
-        {
+        // Enqueueing can throw: the thread_pool construction and asio::post both allocate,
+        // and under memory pressure a throw here would escape glCompileShader leaving the
+        // node Pending with nothing left to dispatch it - the first observable read would
+        // then block the GL thread forever. Settle the node instead: a cancelled node is a
+        // state every joiner already handles.
+        //
+        // `node` is still valid in the catch for every throw this try can produce. The
+        // thread_pool construction runs before the move; deque::push_back is strongly
+        // exception-safe and SharedPtr's move constructor is noexcept, so a throwing
+        // push_back never consumed it; and DispatchLocked contains its own asio::post
+        // failures rather than propagating them (see above). Keep it that way.
+        try {
             const std::lock_guard<std::mutex> lock(m_impl->mutex);
             if (!m_impl->stopped.load(std::memory_order_acquire) && !InProcessTeardown()) {
                 if (!m_impl->pool) m_impl->pool = MakeUnique<asio::thread_pool>(m_impl->threadCount);
@@ -182,12 +228,27 @@ namespace MobileGL::MG_Util::Async {
                 m_impl->DispatchLocked();
                 return;
             }
+        } catch (...) {
+            MGLOG_E("ShaderCompilePool::Post: enqueue failed; cancelling the job so its joiner "
+                    "cannot block forever");
+            if (node) node->Cancel();
+            return;
         }
 
         // A stopped pool is a synchronous pool, not a black hole: the node still runs, just
         // on the caller's thread. Everything downstream already handles "terminal by the time
         // Post returns", because that is exactly what the inline path looks like. Run it
         // outside the lock - a body, or a continuation it releases, is free to Post again.
+        //
+        // Say so once. StopAndDrain is a one-way latch (see its tail), so from the first
+        // eglTerminate onwards EVERY compile in this process silently runs on the GL thread;
+        // without this line the only symptom is that asynchronous compilation stopped helping,
+        // with nothing in the log to point at. Once, not per node: a pack load posts hundreds.
+        static std::atomic<Bool> warnedStopped{false};
+        if (!warnedStopped.exchange(true, std::memory_order_relaxed)) {
+            MGLOG_W("ShaderCompilePool::Post: the pool is stopped (eglTerminate, or process exit); shader "
+                    "compilation runs inline on the calling thread until MobileGL is re-initialized");
+        }
         node->RunInline();
     }
 

MobileGL/MG_Util/ShaderTranspiler/ShaderCompiler.cpp

@@ -249,6 +249,56 @@ namespace MobileGL {
                 return retryResult;
             }
 
+            // Namespace-level rather than a function-local static, because it has to be
+            // CLEARABLE: what PrewarmBuiltins latches is not a property of this process, it is
+            // a property of the built-in symbol tables glslang currently holds, and
+            // glslang::FinalizeProcess() deletes those. A function-local latch survived the
+            // teardown that invalidated it, so an Initialize -> Destroy -> Initialize cycle
+            // came back up with the tables gone and the prewarm skipped - which is exactly the
+            // serialized-first-parse stall this function exists to prevent, only now
+            // unfixable for the rest of the process. Reset it from DestroyImpl.
+            namespace {
+                Bool g_builtinsPrewarmed = false;
+            } // namespace
+
+            void ShaderCompiler::ResetPrewarmLatch() { g_builtinsPrewarmed = false; }
+
+            void ShaderCompiler::PrewarmBuiltins() {
+                if (g_builtinsPrewarmed) return;
+                g_builtinsPrewarmed = true;
+
+                // One vertex and one fragment shader is enough: the built-in table is cached
+                // per (version, spvVersion, profile, source), not per stage language, and
+                // both configurations CompileShader can reach - the declared-460 path and
+                // the retargeted-legacy path - resolve to the same combination here because
+                // ParseShaderSource always passes 460/ECoreProfile as the default. Parsing
+                // both anyway costs microseconds and keeps this honest if that ever changes.
+                static constexpr const char* kPrewarmVertexSource =
+                    "#version 460\nvoid main() { gl_Position = vec4(0.0); }\n";
+                static constexpr const char* kPrewarmFragmentSource =
+                    "#version 460\nlayout(location = 0) out vec4 c;\nvoid main() { c = vec4(0.0); }\n";
+                static constexpr const char* kPrewarmLegacyVertexSource =
+                    "#version 330 core\nvoid main() { gl_Position = vec4(0.0); }\n";
+
+                const CompileEnv& env = *GetDefaultCompileEnv();
+                for (const auto& [type, source] :
+                     {std::pair{GL_VERTEX_SHADER, kPrewarmVertexSource},
+                      std::pair{GL_FRAGMENT_SHADER, kPrewarmFragmentSource},
+                      std::pair{GL_VERTEX_SHADER, kPrewarmLegacyVertexSource}}) {
+                    ShaderAttrib attrib{.shaderType = static_cast<GLenum>(type),
+                                        .sourceStr = source,
+                                        .flags = 0,
+                                        .env = &env};
+                    // The result is deliberately discarded: the value is the symbol table
+                    // glslang cached as a side effect. A failure here is not fatal - it just
+                    // means the first real compile pays for the table, exactly as before.
+                    (void)CompileShader(attrib);
+                }
+                // The parses above left this thread's glslang allocator pointing at the last
+                // TShader's pool, and that TShader is about to be destroyed with it.
+                glslang::SetThreadPoolAllocator(nullptr);
+            }
+
             Result<SharedPtr<glslang::TProgram>> ShaderCompiler::LinkProgram(const ProgramAttrib& attrib) {
                 SharedPtr<glslang::TProgram> program = MakeShared<glslang::TProgram>();
                 for (auto& s : attrib.shaders) {

MobileGL/MG_Util/ShaderTranspiler/ShaderCompiler.h

@@ -77,6 +77,30 @@ namespace MobileGL {
                 static bool UseUnformattedFloatStorageImagesForVulkan(
                     const Vector<Uint32>& inputBinary, Vector<uint32_t>& outputBinary);
                 static Result<String> DecompileShader(SpvcSession& session);
+
+                // Parses one trivial shader in each configuration the production path can
+                // reach, on the calling thread, so the built-in symbol tables those
+                // configurations need are already cached before any worker asks for one.
+                //
+                // Why it matters: glslang builds a built-in TSymbolTable per distinct
+                // (version, spvVersion, profile, source) combination, and does it under a
+                // process-wide lock held for the whole build. Without this, the first
+                // parallel compiles of a shaderpack load all pile up behind that lock and
+                // show no speedup at all - which is easy to misread as asynchronous
+                // compilation not working. Call once, from the GL thread, right after
+                // glslang::InitializeProcess(). Idempotent and cheap on repeat.
+                //
+                // Only worth its cost when compiles can actually run in parallel, so the GL
+                // frontend calls it only when asynchronous compilation is enabled: a
+                // synchronous build would pay for three throwaway parses at every
+                // eglInitialize to prewarm tables the first real compile builds anyway.
+                static void PrewarmBuiltins();
+                // Clears the "already prewarmed" latch. MUST be called wherever
+                // glslang::FinalizeProcess() is, and for the same reason: finalizing deletes
+                // the cached built-in tables the latch is asserting the existence of. Without
+                // it, the second eglInitialize of a process comes back up unwarmed and with
+                // no way left to warm it.
+                static void ResetPrewarmLatch();
             };
         } // namespace ShaderTranspiler
     } // namespace MG_Util