deps: backport 6e9e2e5 from upstream V8

Original commit message:

  [heap] Move SweeperTask 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: v8:6655
  Change-Id: Icdaae744ee73146b86b9a28c8035138746721971
  Reviewed-on: https://chromium-review.googlesource.com/595467
  Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
  Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
  Cr-Commit-Position: refs/heads/master@{#47036}

Backport-PR-URL: #15393
PR-URL: #14001
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>

Author: Matt Loring

deps/v8/src/heap/mark-compact.cc

@@ -9,6 +9,7 @@
 #include "src/base/atomicops.h"
 #include "src/base/bits.h"
 #include "src/base/sys-info.h"
+#include "src/cancelable-task.h"
 #include "src/code-stubs.h"
 #include "src/compilation-cache.h"
 #include "src/deoptimizer.h"
@@ -569,21 +570,22 @@ void MarkCompactCollector::ClearMarkbits() {
   heap_->lo_space()->ClearMarkingStateOfLiveObjects();
 }
 
-class MarkCompactCollector::Sweeper::SweeperTask : public v8::Task {
+class MarkCompactCollector::Sweeper::SweeperTask final : public CancelableTask {
  public:
-  SweeperTask(Sweeper* sweeper, base::Semaphore* pending_sweeper_tasks,
+  SweeperTask(Isolate* isolate, Sweeper* sweeper,
+              base::Semaphore* pending_sweeper_tasks,
               base::AtomicNumber<intptr_t>* num_sweeping_tasks,
               AllocationSpace space_to_start)
-      : sweeper_(sweeper),
+      : CancelableTask(isolate),
+        sweeper_(sweeper),
         pending_sweeper_tasks_(pending_sweeper_tasks),
         num_sweeping_tasks_(num_sweeping_tasks),
         space_to_start_(space_to_start) {}
 
   virtual ~SweeperTask() {}
 
  private:
-  // v8::Task overrides.
-  void Run() override {
+  void RunInternal() final {
     DCHECK_GE(space_to_start_, FIRST_SPACE);
     DCHECK_LE(space_to_start_, LAST_PAGED_SPACE);
     const int offset = space_to_start_ - FIRST_SPACE;
@@ -598,9 +600,9 @@ class MarkCompactCollector::Sweeper::SweeperTask : public v8::Task {
     pending_sweeper_tasks_->Signal();
   }
 
-  Sweeper* sweeper_;
-  base::Semaphore* pending_sweeper_tasks_;
-  base::AtomicNumber<intptr_t>* num_sweeping_tasks_;
+  Sweeper* const sweeper_;
+  base::Semaphore* const pending_sweeper_tasks_;
+  base::AtomicNumber<intptr_t>* const num_sweeping_tasks_;
   AllocationSpace space_to_start_;
 
   DISALLOW_COPY_AND_ASSIGN(SweeperTask);
@@ -618,15 +620,19 @@ void MarkCompactCollector::Sweeper::StartSweeping() {
 }
 
 void MarkCompactCollector::Sweeper::StartSweeperTasks() {
+  DCHECK_EQ(0, num_tasks_);
+  DCHECK_EQ(0, num_sweeping_tasks_.Value());
   if (FLAG_concurrent_sweeping && sweeping_in_progress_) {
     ForAllSweepingSpaces([this](AllocationSpace space) {
       if (space == NEW_SPACE) return;
       num_sweeping_tasks_.Increment(1);
-      semaphore_counter_++;
+      SweeperTask* task = new SweeperTask(heap_->isolate(), this,
+                                          &pending_sweeper_tasks_semaphore_,
+                                          &num_sweeping_tasks_, space);
+      DCHECK_LT(num_tasks_, kMaxSweeperTasks);
+      task_ids_[num_tasks_++] = task->id();
       V8::GetCurrentPlatform()->CallOnBackgroundThread(
-          new SweeperTask(this, &pending_sweeper_tasks_semaphore_,
-                          &num_sweeping_tasks_, space),
-          v8::Platform::kShortRunningTask);
+          task, v8::Platform::kShortRunningTask);
     });
   }
 }
@@ -671,10 +677,14 @@ void MarkCompactCollector::Sweeper::EnsureCompleted() {
       [this](AllocationSpace space) { ParallelSweepSpace(space, 0); });
 
   if (FLAG_concurrent_sweeping) {
-    while (semaphore_counter_ > 0) {
-      pending_sweeper_tasks_semaphore_.Wait();
-      semaphore_counter_--;
+    for (int i = 0; i < num_tasks_; i++) {
+      if (heap_->isolate()->cancelable_task_manager()->TryAbort(task_ids_[i]) !=
+          CancelableTaskManager::kTaskAborted) {
+        pending_sweeper_tasks_semaphore_.Wait();
+      }
     }
+    num_tasks_ = 0;
+    num_sweeping_tasks_.SetValue(0);
   }
 
   ForAllSweepingSpaces([this](AllocationSpace space) {

deps/v8/src/heap/mark-compact.h

@@ -491,8 +491,6 @@ class MarkCompactCollector final : public MarkCompactCollectorBase {
 
   class Sweeper {
    public:
-    class SweeperTask;
-
     enum FreeListRebuildingMode { REBUILD_FREE_LIST, IGNORE_FREE_LIST };
     enum ClearOldToNewSlotsMode {
       DO_NOT_CLEAR,
@@ -508,8 +506,8 @@ class MarkCompactCollector final : public MarkCompactCollectorBase {
 
     explicit Sweeper(Heap* heap)
         : heap_(heap),
+          num_tasks_(0),
           pending_sweeper_tasks_semaphore_(0),
-          semaphore_counter_(0),
           sweeping_in_progress_(false),
           num_sweeping_tasks_(0) {}
 
@@ -535,7 +533,10 @@ class MarkCompactCollector final : public MarkCompactCollectorBase {
     Page* GetSweptPageSafe(PagedSpace* space);
 
    private:
+    class SweeperTask;
+
     static const int kAllocationSpaces = LAST_PAGED_SPACE + 1;
+    static const int kMaxSweeperTasks = kAllocationSpaces;
 
     static ClearOldToNewSlotsMode GetClearOldToNewSlotsMode(Page* p);
 
@@ -550,10 +551,10 @@ class MarkCompactCollector final : public MarkCompactCollectorBase {
 
     void PrepareToBeSweptPage(AllocationSpace space, Page* page);
 
-    Heap* heap_;
+    Heap* const heap_;
+    int num_tasks_;
+    uint32_t task_ids_[kMaxSweeperTasks];
     base::Semaphore pending_sweeper_tasks_semaphore_;
-    // Counter is only used for waiting on the semaphore.
-    intptr_t semaphore_counter_;
     base::Mutex mutex_;
     SweptList swept_list_[kAllocationSpaces];
     SweepingList sweeping_list_[kAllocationSpaces];