Use a lock in pages to synchronize sweeper threads to allow others to wait on concurrently swept pa…

src/heap/spaces.h

Index: src/heap/spaces.h
diff --git a/src/heap/spaces.h b/src/heap/spaces.h
index 3461de3ef009f18d9549a8de8f18ce831ba2f572..ca4fe9526b9c4f74292dcb7d898d15896e03aaa3 100644
--- a/src/heap/spaces.h
+++ b/src/heap/spaces.h
@@ -452,10 +452,14 @@ class MemoryChunk {
     base::Release_Store(&parallel_sweeping_, state);
   }
 
-  bool TryParallelSweeping() {
-    return base::Acquire_CompareAndSwap(&parallel_sweeping_, SWEEPING_PENDING,
-                                        SWEEPING_IN_PROGRESS) ==
-           SWEEPING_PENDING;
+  bool TryLock() { return mutex_->TryLock(); }
+
+  base::Mutex* mutex() { return mutex_; }
+
+  void WaitUntilSweepingCompleted() {
+    mutex_->Lock();
+    mutex_->Unlock();
+    DCHECK(SweepingCompleted());
   }
 
   bool SweepingCompleted() { return parallel_sweeping() <= SWEEPING_FINALIZE; }
@@ -537,9 +541,10 @@ class MemoryChunk {
   static const size_t kWriteBarrierCounterOffset =
       kSlotsBufferOffset + kPointerSize + kPointerSize;
 
-  static const size_t kHeaderSize =
-      kWriteBarrierCounterOffset + kPointerSize + kIntSize + kIntSize +
-      kPointerSize + 5 * kPointerSize + kPointerSize + kPointerSize;
+  static const size_t kHeaderSize = kWriteBarrierCounterOffset + kPointerSize +
+                                    kIntSize + kIntSize + kPointerSize +
+                                    5 * kPointerSize + kPointerSize +
+                                    kPointerSize + kPointerSize;

[Michael Lippautz, 2015/07/22 13:17:01]

Can we make this more verbose by adding a comment? E.g.:
 + kXXX  // ...
 + kPointerSize  // Field: mutex_

[Hannes Payer (out of office), 2015/07/22 13:29:25]

Done.

 
   static const int kBodyOffset =
       CODE_POINTER_ALIGN(kHeaderSize + Bitmap::kSize);
@@ -675,6 +680,7 @@ class MemoryChunk {
   // count highest number of bytes ever allocated on the page.
   int high_water_mark_;
 
+  base::Mutex* mutex_;
   base::AtomicWord parallel_sweeping_;
 
   // PagedSpace free-list statistics.