deps: backport f9c4b7a from upstream V8

Original commit message:

  [heap] Move UnmapFreeMemoryTask to CancelableTask
  This mitigates the problem of blocking on the main thread when the
  platform is unable to execute background tasks in a timely manner.

  Bug: v8:6671
  Change-Id: I741d4b7594e8d62721dad32cbfb19551ffacd0c3
  Reviewed-on: https://chromium-review.googlesource.com/599528
  Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
  Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
  Cr-Commit-Position: refs/heads/master@{#47126}

PR-URL: https://github.com/nodejs/node/pull/14001
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>

deps/v8/src/heap/heap.cc

@@ -161,6 +161,7 @@ Heap::Heap()
       heap_iterator_depth_(0),
       local_embedder_heap_tracer_(nullptr),
       fast_promotion_mode_(false),
+      use_tasks_(true),
       force_oom_(false),
       delay_sweeper_tasks_for_testing_(false),
       pending_layout_change_object_(nullptr) {
@@ -5823,6 +5824,7 @@ void Heap::RegisterExternallyReferencedObject(Object** object) {
 }
 
 void Heap::TearDown() {
+  use_tasks_ = false;
 #ifdef VERIFY_HEAP
   if (FLAG_verify_heap) {
     Verify();

deps/v8/src/heap/heap.h

@@ -1016,6 +1016,8 @@ class Heap {
   // Returns whether SetUp has been called.
   bool HasBeenSetUp();
 
+  bool use_tasks() const { return use_tasks_; }
+
   // ===========================================================================
   // Getters for spaces. =======================================================
   // ===========================================================================
@@ -2375,6 +2377,8 @@ class Heap {
 
   bool fast_promotion_mode_;
 
+  bool use_tasks_;
+
   // Used for testing purposes.
   bool force_oom_;
   bool delay_sweeper_tasks_for_testing_;

deps/v8/src/heap/spaces.cc

@@ -300,7 +300,7 @@ MemoryAllocator::MemoryAllocator(Isolate* isolate)
       size_executable_(0),
       lowest_ever_allocated_(reinterpret_cast<void*>(-1)),
       highest_ever_allocated_(reinterpret_cast<void*>(0)),
-      unmapper_(this) {}
+      unmapper_(isolate->heap(), this) {}
 
 bool MemoryAllocator::SetUp(size_t capacity, size_t code_range_size) {
   capacity_ = RoundUp(capacity, Page::kPageSize);
@@ -332,40 +332,46 @@ void MemoryAllocator::TearDown() {
   code_range_ = nullptr;
 }
 
-class MemoryAllocator::Unmapper::UnmapFreeMemoryTask : public v8::Task {
+class MemoryAllocator::Unmapper::UnmapFreeMemoryTask : public CancelableTask {
  public:
-  explicit UnmapFreeMemoryTask(Unmapper* unmapper) : unmapper_(unmapper) {}
+  explicit UnmapFreeMemoryTask(Isolate* isolate, Unmapper* unmapper)
+      : CancelableTask(isolate), unmapper_(unmapper) {}
 
  private:
-  // v8::Task overrides.
-  void Run() override {
+  void RunInternal() override {
     unmapper_->PerformFreeMemoryOnQueuedChunks<FreeMode::kUncommitPooled>();
     unmapper_->pending_unmapping_tasks_semaphore_.Signal();
   }
 
-  Unmapper* unmapper_;
+  Unmapper* const unmapper_;
   DISALLOW_COPY_AND_ASSIGN(UnmapFreeMemoryTask);
 };
 
 void MemoryAllocator::Unmapper::FreeQueuedChunks() {
   ReconsiderDelayedChunks();
-  if (FLAG_concurrent_sweeping) {
+  if (heap_->use_tasks() && FLAG_concurrent_sweeping) {
+    if (concurrent_unmapping_tasks_active_ >= kMaxUnmapperTasks) {
+      // kMaxUnmapperTasks are already running. Avoid creating any more.
+      return;
+    }
+    UnmapFreeMemoryTask* task = new UnmapFreeMemoryTask(heap_->isolate(), this);
+    DCHECK_LT(concurrent_unmapping_tasks_active_, kMaxUnmapperTasks);
+    task_ids_[concurrent_unmapping_tasks_active_++] = task->id();
     V8::GetCurrentPlatform()->CallOnBackgroundThread(
-        new UnmapFreeMemoryTask(this), v8::Platform::kShortRunningTask);
-    concurrent_unmapping_tasks_active_++;
+        task, v8::Platform::kShortRunningTask);
   } else {
     PerformFreeMemoryOnQueuedChunks<FreeMode::kUncommitPooled>();
   }
 }
 
-bool MemoryAllocator::Unmapper::WaitUntilCompleted() {
-  bool waited = false;
-  while (concurrent_unmapping_tasks_active_ > 0) {
-    pending_unmapping_tasks_semaphore_.Wait();
-    concurrent_unmapping_tasks_active_--;
-    waited = true;
+void MemoryAllocator::Unmapper::WaitUntilCompleted() {
+  for (int i = 0; i < concurrent_unmapping_tasks_active_; i++) {
+    if (heap_->isolate()->cancelable_task_manager()->TryAbort(task_ids_[i]) !=
+        CancelableTaskManager::kTaskAborted) {
+      pending_unmapping_tasks_semaphore_.Wait();
+    }
+    concurrent_unmapping_tasks_active_ = 0;
   }
-  return waited;
 }
 
 template <MemoryAllocator::Unmapper::FreeMode mode>
@@ -392,7 +398,7 @@ void MemoryAllocator::Unmapper::PerformFreeMemoryOnQueuedChunks() {
 }
 
 void MemoryAllocator::Unmapper::TearDown() {
-  WaitUntilCompleted();
+  CHECK_EQ(0, concurrent_unmapping_tasks_active_);
   ReconsiderDelayedChunks();
   CHECK(delayed_regular_chunks_.empty());
   PerformFreeMemoryOnQueuedChunks<FreeMode::kReleasePooled>();

deps/v8/src/heap/spaces.h

@@ -15,6 +15,7 @@
 #include "src/base/bits.h"
 #include "src/base/hashmap.h"
 #include "src/base/platform/mutex.h"
+#include "src/cancelable-task.h"
 #include "src/flags.h"
 #include "src/globals.h"
 #include "src/heap/heap.h"
@@ -1149,8 +1150,9 @@ class V8_EXPORT_PRIVATE MemoryAllocator {
    public:
     class UnmapFreeMemoryTask;
 
-    explicit Unmapper(MemoryAllocator* allocator)
-        : allocator_(allocator),
+    Unmapper(Heap* heap, MemoryAllocator* allocator)
+        : heap_(heap),
+          allocator_(allocator),
           pending_unmapping_tasks_semaphore_(0),
           concurrent_unmapping_tasks_active_(0) {
       chunks_[kRegular].reserve(kReservedQueueingSlots);
@@ -1184,13 +1186,14 @@ class V8_EXPORT_PRIVATE MemoryAllocator {
     }
 
     void FreeQueuedChunks();
-    bool WaitUntilCompleted();
+    void WaitUntilCompleted();
     void TearDown();
 
     bool has_delayed_chunks() { return delayed_regular_chunks_.size() > 0; }
 
    private:
     static const int kReservedQueueingSlots = 64;
+    static const int kMaxUnmapperTasks = 24;
 
     enum ChunkQueueType {
       kRegular,     // Pages of kPageSize that do not live in a CodeRange and
@@ -1229,13 +1232,15 @@ class V8_EXPORT_PRIVATE MemoryAllocator {
     template <FreeMode mode>
     void PerformFreeMemoryOnQueuedChunks();
 
+    Heap* const heap_;
+    MemoryAllocator* const allocator_;
     base::Mutex mutex_;
-    MemoryAllocator* allocator_;
     std::vector<MemoryChunk*> chunks_[kNumberOfChunkQueues];
     // Delayed chunks cannot be processed in the current unmapping cycle because
     // of dependencies such as an active sweeper.
     // See MemoryAllocator::CanFreeMemoryChunk.
     std::list<MemoryChunk*> delayed_regular_chunks_;
+    CancelableTaskManager::Id task_ids_[kMaxUnmapperTasks];
     base::Semaphore pending_unmapping_tasks_semaphore_;
     intptr_t concurrent_unmapping_tasks_active_;
 

deps/v8/src/isolate.cc

@@ -2455,6 +2455,7 @@ void Isolate::Deinit() {
   }
 
   heap_.mark_compact_collector()->EnsureSweepingCompleted();
+  heap_.memory_allocator()->unmapper()->WaitUntilCompleted();
 
   DumpAndResetStats();
 

deps/v8/test/cctest/heap/test-spaces.cc

@@ -370,6 +370,7 @@ TEST(NewSpace) {
   }
 
   new_space.TearDown();
+  memory_allocator->unmapper()->WaitUntilCompleted();
   memory_allocator->TearDown();
   delete memory_allocator;
 }