[heap] Uncommit marking deque in concurrent task.

src/heap/mark-compact.h

Index: src/heap/mark-compact.h
diff --git a/src/heap/mark-compact.h b/src/heap/mark-compact.h
index 7203ad05c0eda3e9afb309149d725cc066930191..a13fb9f73e0de3b814f9b27f330d11e5fa57154b 100644
--- a/src/heap/mark-compact.h
+++ b/src/heap/mark-compact.h
@@ -8,6 +8,7 @@
 #include <deque>
 
 #include "src/base/bits.h"
+#include "src/base/platform/condition-variable.h"
 #include "src/heap/marking.h"
 #include "src/heap/spaces.h"
 #include "src/heap/store-buffer.h"
@@ -60,7 +61,8 @@ class MarkingDeque {
         bottom_(0),
         mask_(0),
         overflowed_(false),
-        in_use_(false) {}
+        in_use_(false),
+        uncommit_task_pending_(false) {}
 
   void SetUp();
   void TearDown();
@@ -122,12 +124,43 @@ class MarkingDeque {
   void set_top(int top) { top_ = top; }
 
  private:
+  class UncommitTask : public v8::Task {
+   public:
+    explicit UncommitTask(MarkingDeque* marking_deque)
+        : marking_deque_(marking_deque) {}
+
+   private:
+    // v8::Task overrides.
+    void Run() override {
+      base::LockGuard<base::Mutex> guard(&marking_deque_->mutex_);
+      if (!marking_deque_->in_use_) {

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

Can you somewhere document with a comment that in_use_ is used to indicate
whether the deque still needs to be uncommitted? Was quite puzzled how the
StartUsing() can get away without explicit waiting for the task.

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

Done.

+        marking_deque_->Uncommit();
+      }
+      marking_deque_->uncommit_task_pending_ = false;
+      marking_deque_->uncommit_task_barrier_.NotifyOne();
+    }
+
+    MarkingDeque* marking_deque_;
+    DISALLOW_COPY_AND_ASSIGN(UncommitTask);
+  };
+
   static const size_t kMaxSize = 4 * MB;
   static const size_t kMinSize = 256 * KB;
 
+  // Must be called with mutex lock.
   void EnsureCommitted();
+
+  // Must be called with mutex lock.
   void Uncommit();
 
+  // Must be called with mutex lock.
+  void StartUncommitTask();
+
+  void WaitForUncommitTask();
+
+  base::Mutex mutex_;
+  base::ConditionVariable uncommit_task_barrier_;
+
   base::VirtualMemory* backing_store_;
   size_t backing_store_committed_size_;
   HeapObject** array_;
@@ -139,6 +172,7 @@ class MarkingDeque {
   int mask_;
   bool overflowed_;
   bool in_use_;
+  bool uncommit_task_pending_;
 
   DISALLOW_COPY_AND_ASSIGN(MarkingDeque);
 };