cppgc: Support incremental marking without non-nested tasks

For the standalone library, some platform implementations might not
support non-nested tasks. We can still offer incremental marking in
such cases using regular tasks and without assuming an empty stack.
(cppgc's default platform e.g. doesn't support non-nested tasks.)

This CL also updates GCInvoker to not trigger an incremental GC if we
won't be able to finalize it. That makes finalizing through an
non-nested incremental task safe.

Bug: chromium:1056170
Change-Id: I85f0c9f2efe643cb87dd65d80417eea0d6ee5d52
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2414217
Commit-Queue: Omer Katz <omerkatz@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69971}

include/cppgc/default-platform.h

@@ -26,8 +26,11 @@ class V8_EXPORT DefaultTaskRunner final : public cppgc::TaskRunner {
   DefaultTaskRunner& operator=(const DefaultTaskRunner&) = delete;
 
   void PostTask(std::unique_ptr<cppgc::Task> task) override;
-  void PostNonNestableTask(std::unique_ptr<cppgc::Task> task) override;
   void PostDelayedTask(std::unique_ptr<cppgc::Task> task, double) override;
+
+  bool NonNestableTasksEnabled() const final { return false; }
+  bool NonNestableDelayedTasksEnabled() const final { return false; }
+  void PostNonNestableTask(std::unique_ptr<cppgc::Task> task) override;
   void PostNonNestableDelayedTask(std::unique_ptr<cppgc::Task> task,
                                   double) override;
 

src/heap/cppgc-js/cpp-heap.cc

@@ -107,7 +107,9 @@ void UnifiedHeapMarker::AddObject(void* object) {
 
 CppHeap::CppHeap(v8::Isolate* isolate, size_t custom_spaces)
     : cppgc::internal::HeapBase(std::make_shared<CppgcPlatformAdapter>(isolate),
-                                custom_spaces),
+                                custom_spaces,
+                                cppgc::internal::HeapBase::StackSupport::
+                                    kSupportsConservativeStackScan),
       isolate_(*reinterpret_cast<Isolate*>(isolate)) {
   CHECK(!FLAG_incremental_marking_wrappers);
 }

src/heap/cppgc/default-platform.cc

@@ -7,6 +7,7 @@
 #include <chrono>  // NOLINT(build/c++11)
 #include <thread>  // NOLINT(build/c++11)
 
+#include "src/base/logging.h"
 #include "src/base/page-allocator.h"
 
 namespace cppgc {
@@ -37,18 +38,18 @@ void DefaultTaskRunner::PostTask(std::unique_ptr<cppgc::Task> task) {
   tasks_.push_back(std::move(task));
 }
 
-void DefaultTaskRunner::PostNonNestableTask(std::unique_ptr<cppgc::Task> task) {
-  PostTask(std::move(task));
-}
-
 void DefaultTaskRunner::PostDelayedTask(std::unique_ptr<cppgc::Task> task,
                                         double) {
   PostTask(std::move(task));
 }
 
-void DefaultTaskRunner::PostNonNestableDelayedTask(
-    std::unique_ptr<cppgc::Task> task, double) {
-  PostTask(std::move(task));
+void DefaultTaskRunner::PostNonNestableTask(std::unique_ptr<cppgc::Task>) {
+  UNREACHABLE();
+}
+
+void DefaultTaskRunner::PostNonNestableDelayedTask(std::unique_ptr<cppgc::Task>,
+                                                   double) {
+  UNREACHABLE();
 }
 
 void DefaultTaskRunner::PostIdleTask(std::unique_ptr<cppgc::IdleTask> task) {

src/heap/cppgc/gc-invoker.cc

@@ -93,6 +93,17 @@ void GCInvoker::GCInvokerImpl::CollectGarbage(GarbageCollector::Config config) {
 
 void GCInvoker::GCInvokerImpl::StartIncrementalGarbageCollection(
     GarbageCollector::Config config) {
+  if ((stack_support_ !=
+       cppgc::Heap::StackSupport::kSupportsConservativeStackScan) &&
+      (!platform_->GetForegroundTaskRunner() ||
+       !platform_->GetForegroundTaskRunner()->NonNestableTasksEnabled())) {
+    // In this configuration the GC finalization can only be triggered through
+    // ForceGarbageCollectionSlow. If incremental GC is started, there is no
+    // way to know how long it will remain enabled (and the write barrier with
+    // it). For that reason, we do not support running incremental GCs in this
+    // configuration.
+    return;
+  }
   // No need to postpone starting incremental GC since the stack is not scanned
   // until GC finalization.
   collector_->StartIncrementalGarbageCollection(config);

src/heap/cppgc/heap-base.cc

@@ -54,7 +54,7 @@ class ObjectSizeCounter : private HeapVisitor<ObjectSizeCounter> {
 }  // namespace
 
 HeapBase::HeapBase(std::shared_ptr<cppgc::Platform> platform,
-                   size_t custom_spaces)
+                   size_t custom_spaces, StackSupport stack_support)
     : raw_heap_(this, custom_spaces),
       platform_(std::move(platform)),
 #if defined(CPPGC_CAGED_HEAP)
@@ -70,7 +70,8 @@ HeapBase::HeapBase(std::shared_ptr<cppgc::Platform> platform,
       prefinalizer_handler_(std::make_unique<PreFinalizerHandler>()),
       object_allocator_(&raw_heap_, page_backend_.get(),
                         stats_collector_.get()),
-      sweeper_(&raw_heap_, platform_.get(), stats_collector_.get()) {
+      sweeper_(&raw_heap_, platform_.get(), stats_collector_.get()),
+      stack_support_(stack_support) {
 }
 
 HeapBase::~HeapBase() = default;

src/heap/cppgc/heap-base.h

@@ -44,6 +44,8 @@ class StatsCollector;
 // Base class for heap implementations.
 class V8_EXPORT_PRIVATE HeapBase {
  public:
+  using StackSupport = cppgc::Heap::StackSupport;
+
   // NoGCScope allows going over limits and avoids triggering garbage
   // collection triggered through allocations or even explicitly.
   class V8_EXPORT_PRIVATE NoGCScope final {
@@ -60,7 +62,8 @@ class V8_EXPORT_PRIVATE HeapBase {
     HeapBase& heap_;
   };
 
-  HeapBase(std::shared_ptr<cppgc::Platform> platform, size_t custom_spaces);
+  HeapBase(std::shared_ptr<cppgc::Platform> platform, size_t custom_spaces,
+           StackSupport stack_support);
   virtual ~HeapBase();
 
   HeapBase(const HeapBase&) = delete;
@@ -116,6 +119,8 @@ class V8_EXPORT_PRIVATE HeapBase {
 
   size_t ObjectPayloadSize() const;
 
+  StackSupport stack_support() const { return stack_support_; }
+
   void AdvanceIncrementalGarbageCollectionOnAllocationIfNeeded();
 
  protected:
@@ -150,6 +155,8 @@ class V8_EXPORT_PRIVATE HeapBase {
 
   size_t no_gc_scope_ = 0;
 
+  const StackSupport stack_support_;
+
   friend class MarkerBase::IncrementalMarkingTask;
   friend class testing::TestWithHeap;
 };

src/heap/cppgc/heap.cc

@@ -77,7 +77,7 @@ void CheckConfig(Heap::Config config) {
 
 Heap::Heap(std::shared_ptr<cppgc::Platform> platform,
            cppgc::Heap::HeapOptions options)
-    : HeapBase(platform, options.custom_spaces.size()),
+    : HeapBase(platform, options.custom_spaces.size(), options.stack_support),
       gc_invoker_(this, platform_.get(), options.stack_support),
       growing_(&gc_invoker_, stats_collector_.get(),
                options.resource_constraints) {}

src/heap/cppgc/marker.cc

@@ -138,27 +138,44 @@ size_t GetNextIncrementalStepDuration(IncrementalMarkingSchedule& schedule,
 
 constexpr v8::base::TimeDelta MarkerBase::kMaximumIncrementalStepDuration;
 
-MarkerBase::IncrementalMarkingTask::IncrementalMarkingTask(MarkerBase* marker)
-    : marker_(marker), handle_(Handle::NonEmptyTag{}) {}
+MarkerBase::IncrementalMarkingTask::IncrementalMarkingTask(
+    MarkerBase* marker, MarkingConfig::StackState stack_state)
+    : marker_(marker),
+      stack_state_(stack_state),
+      handle_(Handle::NonEmptyTag{}) {}
 
 // static
 MarkerBase::IncrementalMarkingTask::Handle
 MarkerBase::IncrementalMarkingTask::Post(v8::TaskRunner* runner,
                                          MarkerBase* marker) {
-  auto task = std::make_unique<IncrementalMarkingTask>(marker);
+  // Incremental GC is possible only via the GCInvoker, so getting here
+  // guarantees that either non-nestable tasks or conservative stack
+  // scannnig are supported. This is required so that the incremental
+  // task can safely finalize GC if needed.
+  DCHECK_IMPLIES(marker->heap().stack_support() !=
+                     HeapBase::StackSupport::kSupportsConservativeStackScan,
+                 runner->NonNestableTasksEnabled());
+  MarkingConfig::StackState stack_state_for_task =
+      runner->NonNestableTasksEnabled()
+          ? MarkingConfig::StackState::kNoHeapPointers
+          : MarkingConfig::StackState::kMayContainHeapPointers;
+  auto task =
+      std::make_unique<IncrementalMarkingTask>(marker, stack_state_for_task);
   auto handle = task->handle_;
-  runner->PostNonNestableTask(std::move(task));
+  if (runner->NonNestableTasksEnabled()) {
+    runner->PostNonNestableTask(std::move(task));
+  } else {
+    runner->PostTask(std::move(task));
+  }
   return handle;
 }
 
 void MarkerBase::IncrementalMarkingTask::Run() {
   if (handle_.IsCanceled()) return;
 
-  if (marker_->IncrementalMarkingStep(
-          MarkingConfig::StackState::kNoHeapPointers)) {
+  if (marker_->IncrementalMarkingStep(stack_state_)) {
     // Incremental marking is done so should finalize GC.
-    marker_->heap().FinalizeIncrementalGarbageCollectionIfNeeded(
-        MarkingConfig::StackState::kNoHeapPointers);
+    marker_->heap().FinalizeIncrementalGarbageCollectionIfNeeded(stack_state_);
   }
 }
 

src/heap/cppgc/marker.h

@@ -103,7 +103,7 @@ class V8_EXPORT_PRIVATE MarkerBase {
    public:
     using Handle = SingleThreadedHandle;
 
-    explicit IncrementalMarkingTask(MarkerBase*);
+    IncrementalMarkingTask(MarkerBase*, MarkingConfig::StackState);
 
     static Handle Post(v8::TaskRunner*, MarkerBase*);
 
@@ -111,6 +111,7 @@ class V8_EXPORT_PRIVATE MarkerBase {
     void Run() final;
 
     MarkerBase* const marker_;
+    MarkingConfig::StackState stack_state_;
     // TODO(chromium:1056170): Change to CancelableTask.
     Handle handle_;
   };

test/unittests/heap/cppgc/gc-invoker-unittest.cc

@@ -129,7 +129,8 @@ TEST(GCInvokerTest, IncrementalGCIsStarted) {
   EXPECT_CALL(
       gc, StartIncrementalGarbageCollection(::testing::Field(
               &GarbageCollector::Config::stack_state,
-              GarbageCollector::Config::StackState::kMayContainHeapPointers)));
+              GarbageCollector::Config::StackState::kMayContainHeapPointers)))
+      .Times(0);
   invoker_without_support.StartIncrementalGarbageCollection(
       GarbageCollector::Config::ConservativeIncrementalConfig());
 }