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..f592796ec59d499f1d76434da72aec795277b8d5 100644
--- a/src/heap/spaces.h
+++ b/src/heap/spaces.h
@@ -452,10 +452,17 @@ 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_; }
+
+  // WaitUntilSweepingCompleted only works when concurrent sweeping is in
+  // progress. In particular, when we know that right before this call a
+  // sweeper thread was sweeping this page.
+  void WaitUntilSweepingCompleted() {
+    mutex_->Lock();
+    mutex_->Unlock();
+    DCHECK(SweepingCompleted());
   }
 
   bool SweepingCompleted() { return parallel_sweeping() <= SWEEPING_FINALIZE; }
@@ -537,9 +544,15 @@ 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 +  // write_barrier_counter_
+                                    kIntSize +      // progress_bar_
+                                    kIntSize +      // high_water_mark_
+                                    kPointerSize +  // mutex_ page lock
+                                    kPointerSize +  // parallel_sweeping_
+                                    5 * kPointerSize +  // free list statistics
+                                    kPointerSize +      // next_chunk_
+                                    kPointerSize;       // prev_chunk_
 
   static const int kBodyOffset =
       CODE_POINTER_ALIGN(kHeaderSize + Bitmap::kSize);
@@ -675,6 +688,7 @@ 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.