cppgc: Port concurrent sweeper

This moves concurrent and incremental sweeping from Blink. This also
adds TestPlatform that makes it easier to test concurrent and
incremental sweeping.

Drive-by: fix unmarking of large pages.

Bug: chromium:1056170
Change-Id: Ifd50ff67b9df17ff117a5f4d4eb5a2937d3023be
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2207132
Commit-Queue: Anton Bikineev <bikineev@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Omer Katz <omerkatz@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67969}

include/cppgc/platform.h

@@ -10,13 +10,16 @@
 
 namespace cppgc {
 
-// TODO(v8:10346): Put PageAllocator in a non-V8 include header to avoid
-// depending on namespace v8.
+// TODO(v8:10346): Put PageAllocator and Platform in a non-V8 include header to
+// avoid depending on namespace v8.
 using PageAllocator = v8::PageAllocator;
+using Platform = v8::Platform;
 
 // Initializes the garbage collector with the provided platform. Must be called
 // before creating a Heap.
-V8_EXPORT void InitializePlatform(PageAllocator* page_allocator);
+V8_EXPORT void InitializePlatform(Platform* platform);
+
+V8_EXPORT Platform* GetPlatform();
 
 // Must be called after destroying the last used heap.
 V8_EXPORT void ShutdownPlatform();

src/heap/cppgc/heap-page.cc

@@ -73,6 +73,15 @@ const BasePage* BasePage::FromInnerAddress(const Heap* heap,
       heap->page_backend()->Lookup(static_cast<ConstAddress>(address)));
 }
 
+// static
+void BasePage::Destroy(BasePage* page) {
+  if (page->is_large()) {
+    LargePage::Destroy(LargePage::From(page));
+  } else {
+    NormalPage::Destroy(NormalPage::From(page));
+  }
+}
+
 HeapObjectHeader& BasePage::ObjectHeaderFromInnerAddress(void* address) const {
   return const_cast<HeapObjectHeader&>(
       ObjectHeaderFromInnerAddress(const_cast<const void*>(address)));

src/heap/cppgc/heap-page.h

@@ -28,6 +28,8 @@ class V8_EXPORT_PRIVATE BasePage {
   static BasePage* FromInnerAddress(const Heap*, void*);
   static const BasePage* FromInnerAddress(const Heap*, const void*);
 
+  static void Destroy(BasePage*);
+
   BasePage(const BasePage&) = delete;
   BasePage& operator=(const BasePage&) = delete;
 
@@ -141,15 +143,15 @@ class V8_EXPORT_PRIVATE NormalPage final : public BasePage {
 
   static size_t PayloadSize();
 
+  bool PayloadContains(ConstAddress address) const {
+    return (PayloadStart() <= address) && (address < PayloadEnd());
+  }
+
   ObjectStartBitmap& object_start_bitmap() { return object_start_bitmap_; }
   const ObjectStartBitmap& object_start_bitmap() const {
     return object_start_bitmap_;
   }
 
-  bool PayloadContains(ConstAddress address) const {
-    return (PayloadStart() <= address) && (address < PayloadEnd());
-  }
-
  private:
   NormalPage(Heap* heap, BaseSpace* space);
   ~NormalPage();

src/heap/cppgc/heap-space.cc

@@ -7,6 +7,7 @@
 #include <algorithm>
 
 #include "src/base/logging.h"
+#include "src/base/platform/mutex.h"
 #include "src/heap/cppgc/heap-page.h"
 #include "src/heap/cppgc/object-start-bitmap-inl.h"
 
@@ -17,11 +18,13 @@ BaseSpace::BaseSpace(RawHeap* heap, size_t index, PageType type)
     : heap_(heap), index_(index), type_(type) {}
 
 void BaseSpace::AddPage(BasePage* page) {
+  v8::base::LockGuard<v8::base::Mutex> lock(&pages_mutex_);
   DCHECK_EQ(pages_.cend(), std::find(pages_.cbegin(), pages_.cend(), page));
   pages_.push_back(page);
 }
 
 void BaseSpace::RemovePage(BasePage* page) {
+  v8::base::LockGuard<v8::base::Mutex> lock(&pages_mutex_);
   auto it = std::find(pages_.cbegin(), pages_.cend(), page);
   DCHECK_NE(pages_.cend(), it);
   pages_.erase(it);

src/heap/cppgc/heap-space.h

@@ -9,6 +9,7 @@
 
 #include "src/base/logging.h"
 #include "src/base/macros.h"
+#include "src/base/platform/mutex.h"
 #include "src/heap/cppgc/free-list.h"
 
 namespace cppgc {
@@ -53,6 +54,7 @@ class V8_EXPORT_PRIVATE BaseSpace {
  private:
   RawHeap* heap_;
   Pages pages_;
+  v8::base::Mutex pages_mutex_;
   const size_t index_;
   const PageType type_;
 };

src/heap/cppgc/heap.cc

@@ -116,7 +116,7 @@ void Heap::CollectGarbage(GCConfig config) {
   marker_.reset();
   {
     NoGCScope no_gc(this);
-    sweeper_.Start(Sweeper::Config::kAtomic);
+    sweeper_.Start(config.sweep_type);
   }
 }
 

src/heap/cppgc/heap.h

@@ -68,10 +68,14 @@ class V8_EXPORT_PRIVATE Heap final : public cppgc::Heap {
 
   struct GCConfig {
     using StackState = Heap::StackState;
+    using SweepType = Sweeper::Config;
 
-    static GCConfig Default() { return {StackState::kMayContainHeapPointers}; }
+    static GCConfig Default() {
+      return {StackState::kMayContainHeapPointers, SweepType::kAtomic};
+    }
 
     StackState stack_state = StackState::kMayContainHeapPointers;
+    SweepType sweep_type = SweepType::kAtomic;
   };
 
   static Heap* From(cppgc::Heap* heap) { return static_cast<Heap*>(heap); }

src/heap/cppgc/platform.cc

@@ -10,16 +10,18 @@
 namespace cppgc {
 namespace internal {
 
-static PageAllocator* g_page_allocator;
+static Platform* g_platform;
 
 }  // namespace internal
 
-void InitializePlatform(PageAllocator* page_allocator) {
-  internal::g_page_allocator = page_allocator;
-  internal::GlobalGCInfoTable::Create(page_allocator);
+void InitializePlatform(Platform* platform) {
+  internal::g_platform = platform;
+  internal::GlobalGCInfoTable::Create(internal::g_platform->GetPageAllocator());
 }
 
-void ShutdownPlatform() { internal::g_page_allocator = nullptr; }
+Platform* GetPlatform() { return internal::g_platform; }
+
+void ShutdownPlatform() { internal::g_platform = nullptr; }
 
 namespace internal {
 

src/heap/cppgc/sweeper.cc

@@ -4,8 +4,13 @@
 
 #include "src/heap/cppgc/sweeper.h"
 
+#include <atomic>
+#include <memory>
 #include <vector>
 
+#include "include/cppgc/platform.h"
+#include "src/base/optional.h"
+#include "src/base/platform/mutex.h"
 #include "src/heap/cppgc/free-list.h"
 #include "src/heap/cppgc/globals.h"
 #include "src/heap/cppgc/heap-object-header-inl.h"
@@ -23,6 +28,8 @@ namespace internal {
 
 namespace {
 
+using v8::base::Optional;
+
 class ObjectStartBitmapVerifier
     : private HeapVisitor<ObjectStartBitmapVerifier> {
   friend class HeapVisitor<ObjectStartBitmapVerifier>;
@@ -54,15 +61,119 @@ class ObjectStartBitmapVerifier
   HeapObjectHeader* prev_ = nullptr;
 };
 
+template <typename T>
+class ThreadSafeStack {
+ public:
+  ThreadSafeStack() = default;
+
+  void Push(T t) {
+    v8::base::LockGuard<v8::base::Mutex> lock(&mutex_);
+    vector_.push_back(std::move(t));
+  }
+
+  Optional<T> Pop() {
+    v8::base::LockGuard<v8::base::Mutex> lock(&mutex_);
+    if (vector_.empty()) return v8::base::nullopt;
+    T top = std::move(vector_.back());
+    vector_.pop_back();
+    // std::move is redundant but is needed to avoid the bug in gcc-7.
+    return std::move(top);
+  }
+
+  template <typename It>
+  void Insert(It begin, It end) {
+    v8::base::LockGuard<v8::base::Mutex> lock(&mutex_);
+    vector_.insert(vector_.end(), begin, end);
+  }
+
+  bool IsEmpty() const {
+    v8::base::LockGuard<v8::base::Mutex> lock(&mutex_);
+    return vector_.empty();
+  }
+
+ private:
+  std::vector<T> vector_;
+  mutable v8::base::Mutex mutex_;
+};
+
 struct SpaceState {
-  BaseSpace::Pages unswept_pages;
+  struct SweptPageState {
+    BasePage* page = nullptr;
+    std::vector<HeapObjectHeader*> unfinalized_objects;
+    FreeList cached_free_list;
+    std::vector<FreeList::Block> unfinalized_free_list;
+    bool is_empty = false;
+  };
+
+  ThreadSafeStack<BasePage*> unswept_pages;
+  ThreadSafeStack<SweptPageState> swept_unfinalized_pages;
 };
+
 using SpaceStates = std::vector<SpaceState>;
 
-bool SweepNormalPage(NormalPage* page) {
+// Builder that finalizes objects and adds freelist entries right away.
+class InlinedFinalizationBuilder final {
+ public:
+  using ResultType = bool;
+
+  explicit InlinedFinalizationBuilder(BasePage* page) : page_(page) {}
+
+  void AddFinalizer(HeapObjectHeader* header, size_t size) {
+    header->Finalize();
+    SET_MEMORY_INACCESIBLE(header, size);
+  }
+
+  void AddFreeListEntry(Address start, size_t size) {
+    auto* space = NormalPageSpace::From(page_->space());
+    space->free_list().Add({start, size});
+  }
+
+  ResultType GetResult(bool is_empty) { return is_empty; }
+
+ private:
+  BasePage* page_;
+};
+
+// Builder that produces results for deferred processing.
+class DeferredFinalizationBuilder final {
+ public:
+  using ResultType = SpaceState::SweptPageState;
+
+  explicit DeferredFinalizationBuilder(BasePage* page) { result_.page = page; }
+
+  void AddFinalizer(HeapObjectHeader* header, size_t size) {
+    if (header->IsFinalizable()) {
+      result_.unfinalized_objects.push_back({header});
+      found_finalizer_ = true;
+    } else {
+      SET_MEMORY_INACCESIBLE(header, size);
+    }
+  }
+
+  void AddFreeListEntry(Address start, size_t size) {
+    if (found_finalizer_) {
+      result_.unfinalized_free_list.push_back({start, size});
+    } else {
+      result_.cached_free_list.Add({start, size});
+    }
+    found_finalizer_ = false;
+  }
+
+  ResultType&& GetResult(bool is_empty) {
+    result_.is_empty = is_empty;
+    return std::move(result_);
+  }
+
+ private:
+  ResultType result_;
+  bool found_finalizer_ = false;
+};
+
+template <typename FinalizationBuilder>
+typename FinalizationBuilder::ResultType SweepNormalPage(NormalPage* page) {
   constexpr auto kAtomicAccess = HeapObjectHeader::AccessMode::kAtomic;
+  FinalizationBuilder builder(page);
 
-  auto* space = NormalPageSpace::From(page->space());
   ObjectStartBitmap& bitmap = page->object_start_bitmap();
   bitmap.Clear();
 
@@ -79,16 +190,16 @@ bool SweepNormalPage(NormalPage* page) {
     }
     // Check if object is not marked (not reachable).
     if (!header->IsMarked<kAtomicAccess>()) {
-      header->Finalize();
-      SET_MEMORY_INACCESIBLE(header, size);
+      builder.AddFinalizer(header, size);
       begin += size;
       continue;
     }
     // The object is alive.
     const Address header_address = reinterpret_cast<Address>(header);
     if (start_of_gap != header_address) {
-      space->AddToFreeList(start_of_gap,
-                           static_cast<size_t>(header_address - start_of_gap));
+      builder.AddFreeListEntry(
+          start_of_gap, static_cast<size_t>(header_address - start_of_gap));
+      bitmap.SetBit(start_of_gap);
     }
     header->Unmark<kAtomicAccess>();
     bitmap.SetBit(begin);
@@ -98,56 +209,150 @@ bool SweepNormalPage(NormalPage* page) {
 
   if (start_of_gap != page->PayloadStart() &&
       start_of_gap != page->PayloadEnd()) {
-    space->AddToFreeList(
+    builder.AddFreeListEntry(
         start_of_gap, static_cast<size_t>(page->PayloadEnd() - start_of_gap));
+    bitmap.SetBit(start_of_gap);
   }
 
   const bool is_empty = (start_of_gap == page->PayloadStart());
-  return is_empty;
+  return builder.GetResult(is_empty);
 }
 
-// This visitor:
-// - resets linear allocation buffers and clears free lists for all spaces;
-// - moves all Heap pages to local Sweeper's state (SpaceStates).
-class PrepareForSweepVisitor final
-    : public HeapVisitor<PrepareForSweepVisitor> {
+// SweepFinalizer is responsible for heap/space/page finalization. Finalization
+// is defined as a step following concurrent sweeping which:
+// - calls finalizers;
+// - returns (unmaps) empty pages;
+// - merges freelists to the space's freelist.
+class SweepFinalizer final {
  public:
-  explicit PrepareForSweepVisitor(SpaceStates* states) : states_(states) {}
+  explicit SweepFinalizer(v8::Platform* platform) : platform_(platform) {}
 
-  bool VisitNormalPageSpace(NormalPageSpace* space) {
-    DCHECK(!space->linear_allocation_buffer().size());
-    space->free_list().Clear();
-    (*states_)[space->index()].unswept_pages = space->RemoveAllPages();
-    return true;
+  void FinalizeHeap(SpaceStates* space_states) {
+    for (SpaceState& space_state : *space_states) {
+      FinalizeSpace(&space_state);
+    }
   }
 
-  bool VisitLargePageSpace(LargePageSpace* space) {
-    (*states_)[space->index()].unswept_pages = space->RemoveAllPages();
+  void FinalizeSpace(SpaceState* space_state) {
+    while (auto page_state = space_state->swept_unfinalized_pages.Pop()) {
+      FinalizePage(&*page_state);
+    }
+  }
+
+  bool FinalizeSpaceWithDeadline(SpaceState* space_state,
+                                 double deadline_in_seconds) {
+    DCHECK(platform_);
+    static constexpr size_t kDeadlineCheckInterval = 8;
+    size_t page_count = 1;
+
+    while (auto page_state = space_state->swept_unfinalized_pages.Pop()) {
+      FinalizePage(&*page_state);
+
+      if (page_count % kDeadlineCheckInterval == 0 &&
+          deadline_in_seconds <= platform_->MonotonicallyIncreasingTime()) {
+        return false;
+      }
+
+      page_count++;
+    }
 
     return true;
   }
 
+  void FinalizePage(SpaceState::SweptPageState* page_state) {
+    DCHECK(page_state);
+    DCHECK(page_state->page);
+    BasePage* page = page_state->page;
+
+    // Call finalizers.
+    for (HeapObjectHeader* object : page_state->unfinalized_objects) {
+      object->Finalize();
+    }
+
+    // Unmap page if empty.
+    if (page_state->is_empty) {
+      BasePage::Destroy(page);
+      return;
+    }
+
+    DCHECK(!page->is_large());
+
+    // Merge freelists without finalizers.
+    FreeList& space_freelist =
+        NormalPageSpace::From(page->space())->free_list();
+    space_freelist.Append(std::move(page_state->cached_free_list));
+
+    // Merge freelist with finalizers.
+    for (auto entry : page_state->unfinalized_free_list) {
+      space_freelist.Add(std::move(entry));
+    }
+
+    // Add the page to the space.
+    page->space()->AddPage(page);
+  }
+
  private:
-  SpaceStates* states_;
+  v8::Platform* platform_;
 };
 
-class MutatorThreadSweepVisitor final
-    : private HeapVisitor<MutatorThreadSweepVisitor> {
-  friend class HeapVisitor<MutatorThreadSweepVisitor>;
+class MutatorThreadSweeper final : private HeapVisitor<MutatorThreadSweeper> {
+  friend class HeapVisitor<MutatorThreadSweeper>;
 
  public:
-  explicit MutatorThreadSweepVisitor(SpaceStates* space_states) {
-    for (SpaceState& state : *space_states) {
-      for (BasePage* page : state.unswept_pages) {
-        Traverse(page);
+  explicit MutatorThreadSweeper(SpaceStates* states, v8::Platform* platform)
+      : states_(states), platform_(platform) {}
+
+  void Sweep() {
+    for (SpaceState& state : *states_) {
+      while (auto page = state.unswept_pages.Pop()) {
+        Traverse(*page);
+      }
+    }
+  }
+
+  bool SweepWithDeadline(double deadline_in_seconds) {
+    DCHECK(platform_);
+    static constexpr double kSlackInSeconds = 0.001;
+    for (SpaceState& state : *states_) {
+      // FinalizeSpaceWithDeadline() and SweepSpaceWithDeadline() won't check
+      // the deadline until it sweeps 10 pages. So we give a small slack for
+      // safety.
+      const double remaining_budget = deadline_in_seconds - kSlackInSeconds -
+                                      platform_->MonotonicallyIncreasingTime();
+      if (remaining_budget <= 0.) return false;
+
+      // First, prioritize finalization of pages that were swept concurrently.
+      SweepFinalizer finalizer(platform_);
+      if (!finalizer.FinalizeSpaceWithDeadline(&state, deadline_in_seconds)) {
+        return false;
+      }
+
+      // Help out the concurrent sweeper.
+      if (!SweepSpaceWithDeadline(&state, deadline_in_seconds)) {
+        return false;
       }
-      state.unswept_pages.clear();
     }
+    return true;
   }
 
  private:
+  bool SweepSpaceWithDeadline(SpaceState* state, double deadline_in_seconds) {
+    static constexpr size_t kDeadlineCheckInterval = 8;
+    size_t page_count = 1;
+    while (auto page = state->unswept_pages.Pop()) {
+      Traverse(*page);
+      if (page_count % kDeadlineCheckInterval == 0 &&
+          deadline_in_seconds <= platform_->MonotonicallyIncreasingTime()) {
+        return false;
+      }
+      page_count++;
+    }
+
+    return true;
+  }
+
   bool VisitNormalPage(NormalPage* page) {
-    const bool is_empty = SweepNormalPage(page);
+    const bool is_empty = SweepNormalPage<InlinedFinalizationBuilder>(page);
     if (is_empty) {
       NormalPage::Destroy(page);
     } else {
@@ -157,53 +362,253 @@ class MutatorThreadSweepVisitor final
   }
 
   bool VisitLargePage(LargePage* page) {
-    if (page->ObjectHeader()->IsMarked()) {
+    HeapObjectHeader* header = page->ObjectHeader();
+    if (header->IsMarked()) {
+      header->Unmark();
       page->space()->AddPage(page);
     } else {
-      page->ObjectHeader()->Finalize();
+      header->Finalize();
       LargePage::Destroy(page);
     }
     return true;
   }
+
+  SpaceStates* states_;
+  v8::Platform* platform_;
+};
+
+class ConcurrentSweepTask final : public v8::JobTask,
+                                  private HeapVisitor<ConcurrentSweepTask> {
+  friend class HeapVisitor<ConcurrentSweepTask>;
+
+ public:
+  explicit ConcurrentSweepTask(SpaceStates* states) : states_(states) {}
+
+  void Run(v8::JobDelegate* delegate) final {
+    for (SpaceState& state : *states_) {
+      while (auto page = state.unswept_pages.Pop()) {
+        Traverse(*page);
+        if (delegate->ShouldYield()) return;
+      }
+    }
+    is_completed_.store(true, std::memory_order_relaxed);
+  }
+
+  size_t GetMaxConcurrency() const final {
+    return is_completed_.load(std::memory_order_relaxed) ? 0 : 1;
+  }
+
+ private:
+  bool VisitNormalPage(NormalPage* page) {
+    SpaceState::SweptPageState sweep_result =
+        SweepNormalPage<DeferredFinalizationBuilder>(page);
+    const size_t space_index = page->space()->index();
+    DCHECK_GT(states_->size(), space_index);
+    SpaceState& space_state = (*states_)[space_index];
+    space_state.swept_unfinalized_pages.Push(std::move(sweep_result));
+    return true;
+  }
+
+  bool VisitLargePage(LargePage* page) {
+    HeapObjectHeader* header = page->ObjectHeader();
+    if (header->IsMarked()) {
+      header->Unmark();
+      page->space()->AddPage(page);
+      return true;
+    }
+    if (!header->IsFinalizable()) {
+      LargePage::Destroy(page);
+      return true;
+    }
+    const size_t space_index = page->space()->index();
+    DCHECK_GT(states_->size(), space_index);
+    SpaceState& state = (*states_)[space_index];
+    state.swept_unfinalized_pages.Push(
+        {page, {page->ObjectHeader()}, {}, {}, true});
+    return true;
+  }
+
+  SpaceStates* states_;
+  std::atomic_bool is_completed_{false};
+};
+
+// This visitor:
+// - resets linear allocation buffers and clears free lists for all spaces;
+// - moves all Heap pages to local Sweeper's state (SpaceStates).
+class PrepareForSweepVisitor final
+    : public HeapVisitor<PrepareForSweepVisitor> {
+ public:
+  explicit PrepareForSweepVisitor(SpaceStates* states) : states_(states) {}
+
+  bool VisitNormalPageSpace(NormalPageSpace* space) {
+    DCHECK(!space->linear_allocation_buffer().size());
+    space->free_list().Clear();
+    ExtractPages(space);
+    return true;
+  }
+
+  bool VisitLargePageSpace(LargePageSpace* space) {
+    ExtractPages(space);
+    return true;
+  }
+
+ private:
+  void ExtractPages(BaseSpace* space) {
+    BaseSpace::Pages space_pages = space->RemoveAllPages();
+    (*states_)[space->index()].unswept_pages.Insert(space_pages.begin(),
+                                                    space_pages.end());
+  }
+
+  SpaceStates* states_;
 };
 
 }  // namespace
 
 class Sweeper::SweeperImpl final {
  public:
-  explicit SweeperImpl(RawHeap* heap) : heap_(heap) {
-    space_states_.resize(heap_->size());
+  explicit SweeperImpl(RawHeap* heap)
+      : heap_(heap),
+        space_states_(heap->size()),
+        platform_(cppgc::GetPlatform()),
+        foreground_task_runner_(platform_->GetForegroundTaskRunner(nullptr)) {
+    // TODO(chromium:1056170): support Isolate independent task runner.
   }
 
+  ~SweeperImpl() { CancelSweepers(); }
+
   void Start(Config config) {
     is_in_progress_ = true;
 #if DEBUG
     ObjectStartBitmapVerifier().Verify(heap_);
 #endif
     PrepareForSweepVisitor(&space_states_).Traverse(heap_);
+
     if (config == Config::kAtomic) {
       Finish();
     } else {
       DCHECK_EQ(Config::kIncrementalAndConcurrent, config);
-      // TODO(chromium:1056170): Schedule concurrent sweeping.
+      ScheduleIncrementalSweeping();
+      ScheduleConcurrentSweeping();
     }
   }
 
   void Finish() {
     if (!is_in_progress_) return;
 
-    MutatorThreadSweepVisitor s(&space_states_);
+    // First, call finalizers on the mutator thread.
+    SweepFinalizer finalizer(platform_);
+    finalizer.FinalizeHeap(&space_states_);
+
+    // Then, help out the concurrent thread.
+    MutatorThreadSweeper sweeper(&space_states_, platform_);
+    sweeper.Sweep();
+
+    // Synchronize with the concurrent sweeper and call remaining finalizers.
+    SynchronizeAndFinalizeConcurrentSweeping();
 
     is_in_progress_ = false;
   }
 
  private:
-  SpaceStates space_states_;
+  class IncrementalSweepTask : public v8::IdleTask {
+   public:
+    struct Handle {
+      Handle() = default;
+
+      void Cancel() {
+        DCHECK(is_cancelled_);
+        *is_cancelled_ = true;
+      }
+
+      bool IsCanceled() const {
+        DCHECK(is_cancelled_);
+        return *is_cancelled_;
+      }
+
+      explicit operator bool() const { return is_cancelled_.get(); }
+
+     private:
+      struct NonEmptyTag {};
+
+      explicit Handle(NonEmptyTag)
+          : is_cancelled_(std::make_shared<bool>(false)) {}
+
+      std::shared_ptr<bool> is_cancelled_;
+
+      friend class IncrementalSweepTask;
+    };
+
+    explicit IncrementalSweepTask(SweeperImpl* sweeper)
+        : sweeper_(sweeper), handle_(Handle::NonEmptyTag{}) {}
+
+    static Handle Post(SweeperImpl* sweeper, v8::TaskRunner* runner) {
+      auto task = std::make_unique<IncrementalSweepTask>(sweeper);
+      auto handle = task->GetHandle();
+      runner->PostIdleTask(std::move(task));
+      return handle;
+    }
+
+   private:
+    void Run(double deadline_in_seconds) override {
+      if (handle_.IsCanceled() || !sweeper_->is_in_progress_) return;
+
+      MutatorThreadSweeper sweeper(&sweeper_->space_states_,
+                                   sweeper_->platform_);
+      const bool sweep_complete =
+          sweeper.SweepWithDeadline(deadline_in_seconds);
+
+      if (sweep_complete) {
+        sweeper_->SynchronizeAndFinalizeConcurrentSweeping();
+      } else {
+        sweeper_->ScheduleIncrementalSweeping();
+      }
+    }
+
+    Handle GetHandle() const { return handle_; }
+
+    SweeperImpl* sweeper_;
+    // TODO(chromium:1056170): Change to CancelableTask.
+    Handle handle_;
+  };
+
+  void ScheduleIncrementalSweeping() {
+    if (!platform_ || !foreground_task_runner_) return;
+
+    incremental_sweeper_handle_ =
+        IncrementalSweepTask::Post(this, foreground_task_runner_.get());
+  }
+
+  void ScheduleConcurrentSweeping() {
+    if (!platform_) return;
+
+    concurrent_sweeper_handle_ = platform_->PostJob(
+        v8::TaskPriority::kUserVisible,
+        std::make_unique<ConcurrentSweepTask>(&space_states_));
+  }
+
+  void CancelSweepers() {
+    if (incremental_sweeper_handle_) incremental_sweeper_handle_.Cancel();
+    if (concurrent_sweeper_handle_) concurrent_sweeper_handle_->Cancel();
+  }
+
+  void SynchronizeAndFinalizeConcurrentSweeping() {
+    CancelSweepers();
+
+    SweepFinalizer finalizer(platform_);
+    finalizer.FinalizeHeap(&space_states_);
+  }
+
   RawHeap* heap_;
+  SpaceStates space_states_;
+  v8::Platform* platform_;
+  std::shared_ptr<v8::TaskRunner> foreground_task_runner_;
+  IncrementalSweepTask::Handle incremental_sweeper_handle_;
+  std::unique_ptr<v8::JobHandle> concurrent_sweeper_handle_;
   bool is_in_progress_ = false;
 };
 
 Sweeper::Sweeper(RawHeap* heap) : impl_(std::make_unique<SweeperImpl>(heap)) {}
+
 Sweeper::~Sweeper() = default;
 
 void Sweeper::Start(Config config) { impl_->Start(config); }

test/unittests/BUILD.gn

@@ -44,6 +44,7 @@ v8_source_set("cppgc_unittests_sources") {
   testonly = true
 
   sources = [
+    "heap/cppgc/concurrent-sweeper-unittest.cc",
     "heap/cppgc/custom-spaces-unittest.cc",
     "heap/cppgc/finalizer-trait-unittest.cc",
     "heap/cppgc/free-list-unittest.cc",
@@ -63,6 +64,8 @@ v8_source_set("cppgc_unittests_sources") {
     "heap/cppgc/source-location-unittest.cc",
     "heap/cppgc/stack-unittest.cc",
     "heap/cppgc/sweeper-unittest.cc",
+    "heap/cppgc/test-platform.cc",
+    "heap/cppgc/test-platform.h",
     "heap/cppgc/tests.cc",
     "heap/cppgc/tests.h",
     "heap/cppgc/visitor-unittest.cc",

test/unittests/heap/cppgc/concurrent-sweeper-unittest.cc

+// Copyright 2020 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include <algorithm>
+#include <set>
+#include <vector>
+
+#include "include/cppgc/allocation.h"
+#include "include/cppgc/platform.h"
+#include "include/v8-platform.h"
+#include "src/heap/cppgc/globals.h"
+#include "src/heap/cppgc/heap-object-header-inl.h"
+#include "src/heap/cppgc/heap-page.h"
+#include "src/heap/cppgc/heap-space.h"
+#include "src/heap/cppgc/heap-visitor.h"
+#include "src/heap/cppgc/page-memory-inl.h"
+#include "src/heap/cppgc/raw-heap.h"
+#include "src/heap/cppgc/sweeper.h"
+#include "test/unittests/heap/cppgc/test-platform.h"
+#include "test/unittests/heap/cppgc/tests.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace cppgc {
+namespace internal {
+
+namespace {
+
+class ResetLocalAllocationBufferVisitor final
+    : public HeapVisitor<ResetLocalAllocationBufferVisitor> {
+ public:
+  bool VisitLargePageSpace(LargePageSpace*) { return true; }
+  bool VisitNormalPageSpace(NormalPageSpace* space) {
+    space->ResetLinearAllocationBuffer();
+    return true;
+  }
+};
+
+void ResetLocalAllocationBuffers(Heap* heap) {
+  ResetLocalAllocationBufferVisitor visitor;
+  visitor.Traverse(&heap->raw_heap());
+}
+
+size_t g_destructor_callcount;
+
+template <size_t Size>
+class Finalizable : public GarbageCollected<Finalizable<Size>> {
+ public:
+  Finalizable() : creation_thread_{v8::base::OS::GetCurrentThreadId()} {}
+
+  virtual ~Finalizable() {
+    ++g_destructor_callcount;
+    EXPECT_EQ(creation_thread_, v8::base::OS::GetCurrentThreadId());
+  }
+
+  virtual void Trace(cppgc::Visitor*) const {}
+
+ private:
+  char array_[Size];
+  int creation_thread_;
+};
+
+using NormalFinalizable = Finalizable<32>;
+using LargeFinalizable = Finalizable<kLargeObjectSizeThreshold * 2>;
+
+template <size_t Size>
+class NonFinalizable : public GarbageCollected<NonFinalizable<Size>> {
+ public:
+  virtual void Trace(cppgc::Visitor*) const {}
+
+ private:
+  char array_[Size];
+};
+
+using NormalNonFinalizable = NonFinalizable<32>;
+using LargeNonFinalizable = NonFinalizable<kLargeObjectSizeThreshold * 2>;
+
+class ConcurrentSweeperTest : public testing::TestWithHeap {
+ public:
+  ConcurrentSweeperTest() { g_destructor_callcount = 0; }
+
+  void StartSweeping() {
+    Heap* heap = Heap::From(GetHeap());
+    ResetLocalAllocationBuffers(heap);
+    Sweeper& sweeper = heap->sweeper();
+    sweeper.Start(Sweeper::Config::kIncrementalAndConcurrent);
+  }
+
+  void FinishSweeping() {
+    Heap* heap = Heap::From(GetHeap());
+    Sweeper& sweeper = heap->sweeper();
+    sweeper.Finish();
+  }
+
+  const RawHeap& GetRawHeap() const {
+    const Heap* heap = Heap::From(GetHeap());
+    return heap->raw_heap();
+  }
+
+  void CheckFreeListEntries(const std::vector<void*>& objects) {
+    const Heap* heap = Heap::From(GetHeap());
+    const PageBackend* backend = heap->page_backend();
+
+    for (auto* object : objects) {
+      // The corresponding page could be removed.
+      if (!backend->Lookup(static_cast<ConstAddress>(object))) continue;
+
+      const auto* header =
+          BasePage::FromPayload(object)->TryObjectHeaderFromInnerAddress(
+              object);
+      // TryObjectHeaderFromInnerAddress returns nullptr for freelist entries.
+      EXPECT_EQ(nullptr, header);
+    }
+  }
+
+  void CheckPageRemoved(const BasePage* page) {
+    const Heap* heap = Heap::From(GetHeap());
+    const PageBackend* backend = heap->page_backend();
+    EXPECT_EQ(nullptr, backend->Lookup(reinterpret_cast<ConstAddress>(page)));
+  }
+
+  bool FreeListContains(const BaseSpace* space,
+                        const std::vector<void*>& objects) {
+    const Heap* heap = Heap::From(GetHeap());
+    const PageBackend* backend = heap->page_backend();
+    const auto& freelist = NormalPageSpace::From(space)->free_list();
+
+    for (void* object : objects) {
+      // The corresponding page could be removed.
+      if (!backend->Lookup(static_cast<ConstAddress>(object))) continue;
+
+      if (!freelist.Contains({object, 0})) return false;
+    }
+
+    return true;
+  }
+};
+
+}  // namespace
+
+TEST_F(ConcurrentSweeperTest, BackgroundSweepOfNormalPage) {
+  // Non finalizable objects are swept right away.
+  using GCedType = NormalNonFinalizable;
+
+  auto* unmarked_object = MakeGarbageCollected<GCedType>(GetHeap());
+  auto* marked_object = MakeGarbageCollected<GCedType>(GetHeap());
+  HeapObjectHeader::FromPayload(marked_object).TryMarkAtomic();
+
+  auto* page = BasePage::FromPayload(unmarked_object);
+  auto* space = page->space();
+
+  // The test requires objects to be allocated on the same page;
+  ASSERT_EQ(page, BasePage::FromPayload(marked_object));
+
+  StartSweeping();
+
+  // Wait for concurrent sweeping to finish.
+  GetPlatform().WaitAllBackgroundTasks();
+
+  // Check that the marked object was unmarked.
+  EXPECT_FALSE(HeapObjectHeader::FromPayload(marked_object).IsMarked());
+
+  // Check that free list entries are created right away for non-finalizable
+  // objects, but not immediately returned to the space's freelist.
+  CheckFreeListEntries({unmarked_object});
+  EXPECT_FALSE(FreeListContains(space, {unmarked_object}));
+
+  FinishSweeping();
+
+  // Check that finalizable objects are swept and put into the freelist of the
+  // corresponding space.
+  EXPECT_TRUE(FreeListContains(space, {unmarked_object}));
+}
+
+TEST_F(ConcurrentSweeperTest, BackgroundSweepOfLargePage) {
+  // Non finalizable objects are swept right away.
+  using GCedType = LargeNonFinalizable;
+
+  auto* unmarked_object = MakeGarbageCollected<GCedType>(GetHeap());
+  auto* marked_object = MakeGarbageCollected<GCedType>(GetHeap());
+  HeapObjectHeader::FromPayload(marked_object).TryMarkAtomic();
+
+  auto* unmarked_page = BasePage::FromPayload(unmarked_object);
+  auto* marked_page = BasePage::FromPayload(marked_object);
+  auto* space = unmarked_page->space();
+
+  ASSERT_EQ(space, marked_page->space());
+
+  StartSweeping();
+
+  // Wait for concurrent sweeping to finish.
+  GetPlatform().WaitAllBackgroundTasks();
+
+  // Check that the marked object was unmarked.
+  EXPECT_FALSE(HeapObjectHeader::FromPayload(marked_object).IsMarked());
+
+  // Check that free list entries are created right away for non-finalizable
+  // objects, but not immediately returned to the space's freelist.
+  CheckPageRemoved(unmarked_page);
+
+  // Check that marked pages are returned to space right away.
+  EXPECT_NE(space->end(), std::find(space->begin(), space->end(), marked_page));
+
+  FinishSweeping();
+}
+
+TEST_F(ConcurrentSweeperTest, DeferredFinalizationOfNormalPage) {
+  static constexpr size_t kNumberOfObjects = 10;
+  // Finalizable types are left intact by concurrent sweeper.
+  using GCedType = NormalFinalizable;
+
+  std::set<BasePage*> pages;
+  std::vector<void*> objects;
+
+  BaseSpace* space = nullptr;
+  for (size_t i = 0; i < kNumberOfObjects; ++i) {
+    auto* object = MakeGarbageCollected<GCedType>(GetHeap());
+    objects.push_back(object);
+    auto* page = BasePage::FromPayload(object);
+    pages.insert(page);
+    if (!space) space = page->space();
+  }
+
+  StartSweeping();
+
+  // Wait for concurrent sweeping to finish.
+  GetPlatform().WaitAllBackgroundTasks();
+
+  // Check that pages are not returned right away.
+  for (auto* page : pages) {
+    EXPECT_EQ(space->end(), std::find(space->begin(), space->end(), page));
+  }
+  // Check that finalizable objects are left intact in pages.
+  EXPECT_FALSE(FreeListContains(space, objects));
+  // No finalizers have been executed.
+  EXPECT_EQ(0u, g_destructor_callcount);
+
+  FinishSweeping();
+
+  // Check that finalizable objects are swept and turned into freelist entries.
+  CheckFreeListEntries(objects);
+  // Check that space's freelist contains these entries.
+  EXPECT_TRUE(FreeListContains(space, objects));
+  // Check that finalizers have been executed.
+  EXPECT_EQ(kNumberOfObjects, g_destructor_callcount);
+}
+
+TEST_F(ConcurrentSweeperTest, DeferredFinalizationOfLargePage) {
+  using GCedType = LargeFinalizable;
+
+  auto* object = MakeGarbageCollected<GCedType>(GetHeap());
+
+  auto* page = BasePage::FromPayload(object);
+  auto* space = page->space();
+
+  StartSweeping();
+
+  // Wait for concurrent sweeping to finish.
+  GetPlatform().WaitAllBackgroundTasks();
+
+  // Check that the page is not returned to the space.
+  EXPECT_EQ(space->end(), std::find(space->begin(), space->end(), page));
+  // Check that no destructors have been executed yet.
+  EXPECT_EQ(0u, g_destructor_callcount);
+
+  FinishSweeping();
+
+  // Check that the destructor was executed.
+  EXPECT_EQ(1u, g_destructor_callcount);
+  // Check that page was unmapped.
+  CheckPageRemoved(page);
+}
+
+TEST_F(ConcurrentSweeperTest, IncrementalSweeping) {
+  testing::TestPlatform::DisableBackgroundTasksScope disable_concurrent_sweeper(
+      &GetPlatform());
+
+  auto task_runner = GetPlatform().GetForegroundTaskRunner(nullptr);
+
+  // Create two unmarked objects.
+  MakeGarbageCollected<NormalFinalizable>(GetHeap());
+  MakeGarbageCollected<LargeFinalizable>(GetHeap());
+
+  // Create two marked objects.
+  auto* marked_normal_object =
+      MakeGarbageCollected<NormalFinalizable>(GetHeap());
+  auto* marked_large_object = MakeGarbageCollected<LargeFinalizable>(GetHeap());
+
+  auto& marked_normal_header =
+      HeapObjectHeader::FromPayload(marked_normal_object);
+  auto& marked_large_header =
+      HeapObjectHeader::FromPayload(marked_large_object);
+
+  marked_normal_header.TryMarkAtomic();
+  marked_large_header.TryMarkAtomic();
+
+  StartSweeping();
+
+  EXPECT_EQ(0u, g_destructor_callcount);
+  EXPECT_TRUE(marked_normal_header.IsMarked());
+  EXPECT_TRUE(marked_large_header.IsMarked());
+
+  // Wait for incremental sweeper to finish.
+  GetPlatform().WaitAllForegroundTasks();
+
+  EXPECT_EQ(2u, g_destructor_callcount);
+  EXPECT_FALSE(marked_normal_header.IsMarked());
+  EXPECT_FALSE(marked_large_header.IsMarked());
+
+  FinishSweeping();
+}
+
+}  // namespace internal
+}  // namespace cppgc

test/unittests/heap/cppgc/sweeper-unittest.cc

@@ -245,5 +245,25 @@ TEST_F(SweeperTest, SweepDoesNotTriggerRecursiveGC) {
   EXPECT_EQ(saved_epoch + 1, internal_heap->epoch());
 }
 
+TEST_F(SweeperTest, UnmarkObjects) {
+  auto* normal_object = MakeGarbageCollected<GCed<32>>(GetHeap());
+  auto* large_object =
+      MakeGarbageCollected<GCed<kLargeObjectSizeThreshold * 2>>(GetHeap());
+
+  auto& normal_object_header = HeapObjectHeader::FromPayload(normal_object);
+  auto& large_object_header = HeapObjectHeader::FromPayload(large_object);
+
+  normal_object_header.TryMarkAtomic();
+  large_object_header.TryMarkAtomic();
+
+  EXPECT_TRUE(normal_object_header.IsMarked());
+  EXPECT_TRUE(large_object_header.IsMarked());
+
+  Sweep();
+
+  EXPECT_FALSE(normal_object_header.IsMarked());
+  EXPECT_FALSE(large_object_header.IsMarked());
+}
+
 }  // namespace internal
 }  // namespace cppgc

test/unittests/heap/cppgc/test-platform.cc

+// Copyright 2020 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "test/unittests/heap/cppgc/test-platform.h"
+
+#include "src/base/platform/platform.h"
+#include "src/base/platform/time.h"
+
+namespace cppgc {
+namespace internal {
+namespace testing {
+
+void TestTaskRunner::PostTask(std::unique_ptr<v8::Task> task) {
+  tasks_.push_back(std::move(task));
+}
+
+void TestTaskRunner::PostNonNestableTask(std::unique_ptr<v8::Task> task) {
+  PostTask(std::move(task));
+}
+
+void TestTaskRunner::PostDelayedTask(std::unique_ptr<v8::Task> task, double) {
+  PostTask(std::move(task));
+}
+
+void TestTaskRunner::PostNonNestableDelayedTask(std::unique_ptr<v8::Task> task,
+                                                double) {
+  PostTask(std::move(task));
+}
+
+void TestTaskRunner::PostIdleTask(std::unique_ptr<v8::IdleTask> task) {
+  idle_tasks_.push_back(std::move(task));
+}
+
+bool TestTaskRunner::RunSingleTask() {
+  if (!tasks_.size()) return false;
+
+  tasks_.back()->Run();
+  tasks_.pop_back();
+
+  return true;
+}
+
+bool TestTaskRunner::RunSingleIdleTask(double deadline_in_seconds) {
+  if (!idle_tasks_.size()) return false;
+
+  idle_tasks_.back()->Run(deadline_in_seconds);
+  idle_tasks_.pop_back();
+
+  return true;
+}
+
+void TestTaskRunner::RunUntilIdle() {
+  for (auto& task : tasks_) {
+    task->Run();
+  }
+  tasks_.clear();
+
+  for (auto& task : idle_tasks_) {
+    task->Run(std::numeric_limits<double>::infinity());
+  }
+  idle_tasks_.clear();
+}
+
+class TestPlatform::TestJobHandle : public v8::JobHandle {
+ public:
+  explicit TestJobHandle(const std::shared_ptr<JobThread>& thread)
+      : thread_(thread) {
+    const bool success = thread_->Start();
+    USE(success);
+  }
+
+  void NotifyConcurrencyIncrease() override {}
+  void Join() override { thread_->Join(); }
+  void Cancel() override { Join(); }
+  bool IsRunning() override { return true; }
+
+ private:
+  std::shared_ptr<JobThread> thread_;
+};
+
+TestPlatform::TestPlatform()
+    : foreground_task_runner_(std::make_unique<TestTaskRunner>()) {}
+
+TestPlatform::~TestPlatform() V8_NOEXCEPT { WaitAllBackgroundTasks(); }
+
+void TestPlatform::CallOnWorkerThread(std::unique_ptr<v8::Task> task) {
+  if (AreBackgroundTasksDisabled()) return;
+
+  auto thread = std::make_unique<WorkerThread>(std::move(task));
+  if (thread->Start()) {
+    threads_.push_back(std::move(thread));
+  }
+}
+
+void TestPlatform::CallDelayedOnWorkerThread(std::unique_ptr<v8::Task> task,
+                                             double) {
+  CallOnWorkerThread(std::move(task));
+}
+
+std::unique_ptr<v8::JobHandle> TestPlatform::PostJob(
+    v8::TaskPriority, std::unique_ptr<v8::JobTask> job_task) {
+  if (AreBackgroundTasksDisabled()) return {};
+
+  auto thread = std::make_shared<JobThread>(std::move(job_task));
+  job_threads_.push_back(thread);
+  return std::make_unique<TestJobHandle>(std::move(thread));
+}
+
+double TestPlatform::MonotonicallyIncreasingTime() {
+  return v8::base::TimeTicks::HighResolutionNow().ToInternalValue() /
+         static_cast<double>(v8::base::Time::kMicrosecondsPerSecond);
+}
+
+double TestPlatform::CurrentClockTimeMillis() {
+  return v8::base::OS::TimeCurrentMillis();
+}
+
+void TestPlatform::WaitAllForegroundTasks() {
+  foreground_task_runner_->RunUntilIdle();
+}
+
+void TestPlatform::WaitAllBackgroundTasks() {
+  for (auto& thread : threads_) {
+    thread->Join();
+  }
+  threads_.clear();
+  for (auto& thread : job_threads_) {
+    thread->Join();
+  }
+  threads_.clear();
+}
+
+TestPlatform::DisableBackgroundTasksScope::DisableBackgroundTasksScope(
+    TestPlatform* platform)
+    : platform_(platform) {
+  ++platform_->disabled_background_tasks_;
+}
+
+TestPlatform::DisableBackgroundTasksScope::~DisableBackgroundTasksScope()
+    V8_NOEXCEPT {
+  --platform_->disabled_background_tasks_;
+}
+
+}  // namespace testing
+}  // namespace internal
+}  // namespace cppgc

test/unittests/heap/cppgc/test-platform.h

+// Copyright 2020 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef V8_UNITTESTS_HEAP_CPPGC_TEST_PLATFORM_H_
+#define V8_UNITTESTS_HEAP_CPPGC_TEST_PLATFORM_H_
+
+#include <memory>
+#include <vector>
+
+#include "include/cppgc/platform.h"
+#include "src/base/page-allocator.h"
+#include "src/base/platform/platform.h"
+
+namespace cppgc {
+namespace internal {
+namespace testing {
+
+class TestTaskRunner : public v8::TaskRunner {
+ public:
+  void PostTask(std::unique_ptr<v8::Task> task) override;
+  void PostNonNestableTask(std::unique_ptr<v8::Task> task) override;
+  void PostDelayedTask(std::unique_ptr<v8::Task> task, double) override;
+  void PostNonNestableDelayedTask(std::unique_ptr<v8::Task> task,
+                                  double) override;
+
+  void PostIdleTask(std::unique_ptr<v8::IdleTask> task) override;
+  bool IdleTasksEnabled() override { return true; }
+
+  bool RunSingleTask();
+  bool RunSingleIdleTask(double duration_in_seconds);
+
+  void RunUntilIdle();
+
+ private:
+  std::vector<std::unique_ptr<v8::Task>> tasks_;
+  std::vector<std::unique_ptr<v8::IdleTask>> idle_tasks_;
+};
+
+class TestPlatform : public Platform {
+ public:
+  class DisableBackgroundTasksScope {
+   public:
+    explicit DisableBackgroundTasksScope(TestPlatform*);
+    ~DisableBackgroundTasksScope() V8_NOEXCEPT;
+
+   private:
+    TestPlatform* platform_;
+  };
+
+  TestPlatform();
+  ~TestPlatform() V8_NOEXCEPT override;
+
+  PageAllocator* GetPageAllocator() override { return &page_allocator_; }
+
+  int NumberOfWorkerThreads() override {
+    return static_cast<int>(threads_.size());
+  }
+
+  std::shared_ptr<v8::TaskRunner> GetForegroundTaskRunner(
+      v8::Isolate*) override {
+    return foreground_task_runner_;
+  }
+
+  void CallOnWorkerThread(std::unique_ptr<v8::Task> task) override;
+  void CallDelayedOnWorkerThread(std::unique_ptr<v8::Task> task,
+                                 double) override;
+
+  bool IdleTasksEnabled(v8::Isolate*) override { return true; }
+
+  std::unique_ptr<v8::JobHandle> PostJob(
+      v8::TaskPriority, std::unique_ptr<v8::JobTask> job_task) override;
+
+  double MonotonicallyIncreasingTime() override;
+  double CurrentClockTimeMillis() override;
+
+  v8::TracingController* GetTracingController() override {
+    return &tracing_controller_;
+  }
+
+  void WaitAllForegroundTasks();
+  void WaitAllBackgroundTasks();
+
+ private:
+  class TestJobHandle;
+
+  class WorkerThread : public v8::base::Thread {
+   public:
+    explicit WorkerThread(std::unique_ptr<v8::Task> task)
+        : Thread(Options("worker")), task_(std::move(task)) {}
+
+    void Run() override {
+      if (task_) std::move(task_)->Run();
+    }
+
+   private:
+    std::unique_ptr<v8::Task> task_;
+  };
+
+  class JobThread : public v8::base::Thread {
+   public:
+    explicit JobThread(std::unique_ptr<v8::JobTask> task)
+        : Thread(Options("job")), task_(std::move(task)) {}
+
+    void Run() override {
+      class JobDelegate : public v8::JobDelegate {
+       public:
+        bool ShouldYield() override { return false; }
+        void NotifyConcurrencyIncrease() override {}
+      } delegate;
+
+      if (task_) task_->Run(&delegate);
+    }
+
+   private:
+    std::unique_ptr<v8::JobTask> task_;
+  };
+
+  bool AreBackgroundTasksDisabled() const {
+    return disabled_background_tasks_ > 0;
+  }
+
+  v8::base::PageAllocator page_allocator_;
+  std::shared_ptr<TestTaskRunner> foreground_task_runner_;
+  std::vector<std::unique_ptr<WorkerThread>> threads_;
+  std::vector<std::shared_ptr<JobThread>> job_threads_;
+  v8::TracingController tracing_controller_;
+  size_t disabled_background_tasks_ = 0;
+};
+
+}  // namespace testing
+}  // namespace internal
+}  // namespace cppgc
+
+#endif  // V8_UNITTESTS_HEAP_CPPGC_TEST_PLATFORM_H_

test/unittests/heap/cppgc/tests.cc

@@ -6,23 +6,25 @@
 
 #include <memory>
 
+#include "test/unittests/heap/cppgc/test-platform.h"
+
 namespace cppgc {
 namespace internal {
 namespace testing {
 
 // static
-std::unique_ptr<cppgc::PageAllocator> TestWithPlatform::page_allocator_;
+std::unique_ptr<TestPlatform> TestWithPlatform::platform_;
 
 // static
 void TestWithPlatform::SetUpTestSuite() {
-  page_allocator_ = std::make_unique<v8::base::PageAllocator>();
-  cppgc::InitializePlatform(page_allocator_.get());
+  platform_ = std::make_unique<TestPlatform>();
+  cppgc::InitializePlatform(platform_.get());
 }
 
 // static
 void TestWithPlatform::TearDownTestSuite() {
   cppgc::ShutdownPlatform();
-  page_allocator_.reset();
+  platform_.reset();
 }
 
 TestWithHeap::TestWithHeap() : heap_(Heap::Create()) {}

test/unittests/heap/cppgc/tests.h

@@ -7,8 +7,8 @@
 
 #include "include/cppgc/heap.h"
 #include "include/cppgc/platform.h"
-#include "src/base/page-allocator.h"
 #include "src/heap/cppgc/heap.h"
+#include "test/unittests/heap/cppgc/test-platform.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace cppgc {
@@ -20,8 +20,10 @@ class TestWithPlatform : public ::testing::Test {
   static void SetUpTestSuite();
   static void TearDownTestSuite();
 
+  TestPlatform& GetPlatform() const { return *platform_; }
+
  private:
-  static std::unique_ptr<cppgc::PageAllocator> page_allocator_;
+  static std::unique_ptr<TestPlatform> platform_;
 };
 
 class TestWithHeap : public TestWithPlatform {