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https://github.com/MobileGL-Dev/MobileGL
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[Test] (Espryt): pin the twin table identity contract - a reclaimed slot is a new handle and the stale one resolves to nothing
- Five cases against BackendSlotTable directly, through a stand-in state object that carries
only GetLifetimeId(), so none of them needs a GLContext, a driver or ES entry points.
- The load-bearing one is the ABA: an object dies, the sweep returns its slot, the next
object takes the same slot with a moved generation, and the predecessor handle answers
null instead of the successor twin. That is the property the address key could only paper
over with a weak_ptr.
- Gen moves on reuse and only on reuse; Find never mutates the table (which is what lets
SyncTextureObjectToBackend drop its second Find); a whole table saves, resets with = {} and
restores, which is the shape ScopedDirectGLESTextureBindings needs; and two tables of one
kind agree on a single object handle, because the identity comes from the client allocator
rather than from either table.
This commit is contained in:
Swung0x48
@@ -3132,3 +3132,169 @@ TEST(GetterSanity, CombinedUniformComponentsSaturateInsteadOfOverflowing) {
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MG_State::pGLContext.reset();
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}
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#if MOBILEGL_PIPE_PUSH
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namespace {
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// A stand-in frontend object for the twin table. It carries the one thing the table asks of a
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// state object - GetLifetimeId() - so these cases can pin the identity contract without a
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// GLContext, a driver or a backend twin that would want ES entry points.
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struct FakeStateObject {
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explicit FakeStateObject(MobileGL::Uint64 lifetimeId): m_lifetimeId(lifetimeId) {}
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MobileGL::Uint64 GetLifetimeId() const { return m_lifetimeId; }
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private:
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MobileGL::Uint64 m_lifetimeId;
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};
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struct FakeBackendObject {
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int marker = 0;
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};
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// Kind Query is unused by every shipping path, so these cases cannot disturb the slot space
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// any real twin table allocates out of.
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using FakeSlotTable = MobileGL::MG_Backend::DirectGLES::
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BackendSlotTable<FakeStateObject, FakeBackendObject, MobileGL::MG_Pipe::MGPipeKind::Query>;
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} // namespace
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// The property the whole slice exists for. The pre-P2 registry keyed twins on the frontend heap
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// ADDRESS and defended the recycle with a weak_ptr; here the key is {slot, gen}, so a successor
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// object landing on a slot its predecessor owned is a DIFFERENT handle, and the predecessor's
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// handle resolves to nothing rather than to the successor's twin.
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TEST(DirectGLESSlotTable, ARecycledSlotIsANewHandleAndTheStaleOneResolvesToNothing) {
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using namespace MobileGL;
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FakeSlotTable table;
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auto first = MakeShared<FakeStateObject>(0xA1u);
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table.GetOrCreate(first) = MakeShared<FakeBackendObject>();
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(*table.Find(first.get()))->marker = 1;
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const MG_Pipe::MGPipeHandle firstHandle = table.HandleOf(first.get());
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ASSERT_FALSE(MG_Pipe::MGPipeHandleIsNull(firstHandle));
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EXPECT_EQ(table.LiveCount(), 1u);
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// The frontend object dies and the slot is reclaimed - which is the only moment Gen moves.
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first.reset();
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table.CollectGarbageNow();
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EXPECT_EQ(table.LiveCount(), 0u);
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EXPECT_EQ(table.FindByHandle(firstHandle), nullptr)
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<< "a handle whose object is gone still resolved to a twin";
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auto second = MakeShared<FakeStateObject>(0xA2u);
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table.GetOrCreate(second) = MakeShared<FakeBackendObject>();
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(*table.Find(second.get()))->marker = 2;
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const MG_Pipe::MGPipeHandle secondHandle = table.HandleOf(second.get());
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EXPECT_EQ(secondHandle.Slot, firstHandle.Slot) << "the free list did not hand the slot back";
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EXPECT_NE(secondHandle.Gen, firstHandle.Gen) << "the generation did not move on slot reuse";
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EXPECT_FALSE(firstHandle == secondHandle);
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// The stale handle must not resolve to its successor's twin. This is the ABA the address key
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// could only paper over.
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EXPECT_EQ(table.FindByHandle(firstHandle), nullptr);
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ASSERT_NE(table.FindByHandle(secondHandle), nullptr);
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EXPECT_EQ((*table.FindByHandle(secondHandle))->marker, 2);
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}
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// Gen moves on reuse and ONLY on reuse: a live object that is looked up again, or respecified,
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// keeps the handle it was minted with (MGPipeHandles.h).
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TEST(DirectGLESSlotTable, RepeatedLookupsOfALiveObjectKeepOneHandle) {
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using namespace MobileGL;
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FakeSlotTable table;
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auto object = MakeShared<FakeStateObject>(0xB1u);
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table.GetOrCreate(object) = MakeShared<FakeBackendObject>();
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const MG_Pipe::MGPipeHandle handle = table.HandleOf(object.get());
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for (int i = 0; i < 8; ++i) {
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auto* slot = table.GetOrCreate(object) ? table.Find(object.get()) : nullptr;
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ASSERT_NE(slot, nullptr);
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EXPECT_TRUE(table.HandleOf(object.get()) == handle) << "handle moved on lookup " << i;
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}
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EXPECT_EQ(table.LiveCount(), 1u);
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}
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// The lookup does not mutate the table, which is what lets SyncTextureObjectToBackend stop paying
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// a by-value copy plus a second Find to survive the registry's erase-inside-Find. A dead entry
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// stays put until the sweep, and a live entry's pointer is unaffected by looking up anything else.
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TEST(DirectGLESSlotTable, FindNeverMutatesTheTable) {
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using namespace MobileGL;
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FakeSlotTable table;
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auto kept = MakeShared<FakeStateObject>(0xC1u);
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auto doomed = MakeShared<FakeStateObject>(0xC2u);
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table.GetOrCreate(kept) = MakeShared<FakeBackendObject>();
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table.GetOrCreate(doomed) = MakeShared<FakeBackendObject>();
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auto* keptSlot = table.Find(kept.get());
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ASSERT_NE(keptSlot, nullptr);
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const FakeBackendObject* keptTwin = keptSlot->get();
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doomed.reset();
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// The registry's Find would have erased the expired entry here and relocated the rest of the
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// probe cluster, invalidating keptSlot. This one answers null and touches nothing.
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EXPECT_EQ(table.Find(kept.get()), keptSlot);
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EXPECT_EQ(table.LiveCount(), 2u) << "Find reclaimed a slot; only the sweep may do that";
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EXPECT_EQ(keptSlot->get(), keptTwin);
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table.CollectGarbageNow();
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EXPECT_EQ(table.LiveCount(), 1u);
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EXPECT_EQ(table.Find(kept.get())->get(), keptTwin);
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}
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// ScopedDirectGLESTextureBindings saves a whole twin table by value, resets it with `= {}` and
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// restores it. The slot table has to keep that shape or the fixture stops isolating anything.
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TEST(DirectGLESSlotTable, AWholeTableSavesResetsAndRestores) {
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using namespace MobileGL;
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FakeSlotTable table;
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auto object = MakeShared<FakeStateObject>(0xD1u);
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table.GetOrCreate(object) = MakeShared<FakeBackendObject>();
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(*table.Find(object.get()))->marker = 7;
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const FakeSlotTable saved = table;
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table = {};
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EXPECT_EQ(table.Find(object.get()), nullptr) << "the reset left the twin reachable";
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table = saved;
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ASSERT_NE(table.Find(object.get()), nullptr);
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EXPECT_EQ((*table.Find(object.get()))->marker, 7);
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}
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// The whole point of routing every twin through the client allocator: a table that keeps its own
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// dense array still shares ONE identity per frontend object with every other holder of it.
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TEST(DirectGLESSlotTable, TwoTablesOfTheSameKindAgreeOnOneObjectsHandle) {
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using namespace MobileGL;
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FakeSlotTable a;
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FakeSlotTable b;
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auto object = MakeShared<FakeStateObject>(0xE1u);
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a.GetOrCreate(object) = MakeShared<FakeBackendObject>();
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b.GetOrCreate(object) = MakeShared<FakeBackendObject>();
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EXPECT_TRUE(a.HandleOf(object.get()) == b.HandleOf(object.get()));
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}
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#else
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// G2 wants the pull and the push build to list the SAME ctest entries. The twin table only
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// exists under MOBILEGL_PIPE_PUSH, so in the pull build each case above keeps its name and
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// skips visibly - a vanishing test is exactly what that gate is there to stop.
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TEST(DirectGLESSlotTable, ARecycledSlotIsANewHandleAndTheStaleOneResolvesToNothing) {
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GTEST_SKIP() << "the {slot, gen} twin table is compiled only under MOBILEGL_PIPE_PUSH";
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}
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TEST(DirectGLESSlotTable, RepeatedLookupsOfALiveObjectKeepOneHandle) {
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GTEST_SKIP() << "the {slot, gen} twin table is compiled only under MOBILEGL_PIPE_PUSH";
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}
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TEST(DirectGLESSlotTable, FindNeverMutatesTheTable) {
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GTEST_SKIP() << "the {slot, gen} twin table is compiled only under MOBILEGL_PIPE_PUSH";
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}
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TEST(DirectGLESSlotTable, AWholeTableSavesResetsAndRestores) {
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GTEST_SKIP() << "the {slot, gen} twin table is compiled only under MOBILEGL_PIPE_PUSH";
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}
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TEST(DirectGLESSlotTable, TwoTablesOfTheSameKindAgreeOnOneObjectsHandle) {
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GTEST_SKIP() << "the {slot, gen} twin table is compiled only under MOBILEGL_PIPE_PUSH";
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}
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#endif // MOBILEGL_PIPE_PUSH
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