[heap] Uncommit marking deque in concurrent task.

src/heap/mark-compact.cc

Index: src/heap/mark-compact.cc
diff --git a/src/heap/mark-compact.cc b/src/heap/mark-compact.cc
index 4c12ec05dee7c0a5682f8cca8d43c6b462c39a8e..0463657eafdb83df61af9f7f8fb43c9b246a48a3 100644
--- a/src/heap/mark-compact.cc
+++ b/src/heap/mark-compact.cc
@@ -2115,9 +2115,13 @@ void MarkingDeque::SetUp() {
   }
 }
 
-void MarkingDeque::TearDown() { delete backing_store_; }
+void MarkingDeque::TearDown() {
+  WaitForUncommitTask();

[Michael Lippautz, 2016/10/24 08:43:23]

Maybe for future: Afaik, background tasks provide no guarantee on progress. In
theory, we should make the task cancelable, to be able to abort it here and make
progress on the main thread.

[ulan, 2016/10/24 13:14:09]

I made the task cancelable.

+  delete backing_store_;
+}
 
 void MarkingDeque::StartUsing() {
+  base::LockGuard<base::Mutex> guard(&mutex_);
   if (in_use_) {
     // This can happen in mark-compact GC if the incremental marker already
     // started using the marking deque.
@@ -2137,11 +2141,16 @@ void MarkingDeque::StartUsing() {
 }
 
 void MarkingDeque::StopUsing() {
+  base::LockGuard<base::Mutex> guard(&mutex_);
   DCHECK(IsEmpty());
   DCHECK(!overflowed_);
   top_ = bottom_ = mask_ = 0;
-  Uncommit();
   in_use_ = false;
+  if (FLAG_concurrent_sweeping) {
+    StartUncommitTask();
+  } else {
+    Uncommit();
+  }
 }
 
 void MarkingDeque::Clear() {
@@ -2151,7 +2160,7 @@ void MarkingDeque::Clear() {
 }
 
 void MarkingDeque::Uncommit() {
-  DCHECK(in_use_);
+  DCHECK(!in_use_);
   bool success = backing_store_->Uncommit(backing_store_->address(),
                                           backing_store_committed_size_);
   backing_store_committed_size_ = 0;
@@ -2173,6 +2182,21 @@ void MarkingDeque::EnsureCommitted() {
   }
 }
 
+void MarkingDeque::StartUncommitTask() {
+  if (!uncommit_task_pending_) {
+    uncommit_task_pending_ = true;
+    V8::GetCurrentPlatform()->CallOnBackgroundThread(
+        new UncommitTask(this), v8::Platform::kShortRunningTask);
+  }
+}
+
+void MarkingDeque::WaitForUncommitTask() {
+  base::LockGuard<base::Mutex> guard(&mutex_);
+  while (uncommit_task_pending_) {
+    uncommit_task_barrier_.Wait(&mutex_);
+  }
+}
+
 class MarkCompactCollector::ObjectStatsVisitor
     : public MarkCompactCollector::HeapObjectVisitor {
  public: