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

src/heap/spaces.h

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_HEAP_SPACES_H_
 #define V8_HEAP_SPACES_H_
 
 #include "src/allocation.h"
 #include "src/base/atomicops.h"
 #include "src/base/bits.h"
@@ skipping 434 matching lines @@
 
   ParallelSweepingState parallel_sweeping() {
     return static_cast<ParallelSweepingState>(
         base::Acquire_Load(&parallel_sweeping_));
   }
 
   void set_parallel_sweeping(ParallelSweepingState state) {
     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; }
 
   // Manage live byte count (count of bytes known to be live,
   // because they are marked black).
   void ResetLiveBytes() {
     if (FLAG_gc_verbose) {
       PrintF("ResetLiveBytes:%p:%x->0\n", static_cast<void*>(this),
              live_byte_count_);
@@ skipping 61 matching lines @@
 
   static const intptr_t kLiveBytesOffset =
       kSizeOffset + kPointerSize + kPointerSize + kPointerSize + kPointerSize +
       kPointerSize + kPointerSize + kPointerSize + kPointerSize + kIntSize;
 
   static const size_t kSlotsBufferOffset = kLiveBytesOffset + kIntSize;
 
   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);
 
   // The start offset of the object area in a page. Aligned to both maps and
   // code alignment to be suitable for both.  Also aligned to 32 words because
   // the marking bitmap is arranged in 32 bit chunks.
   static const int kObjectStartAlignment = 32 * kPointerSize;
   static const int kObjectStartOffset =
       kBodyOffset - 1 +
@@ skipping 115 matching lines @@
   SlotsBuffer* slots_buffer_;
   SkipList* skip_list_;
   intptr_t write_barrier_counter_;
   // Used by the incremental marker to keep track of the scanning progress in
   // large objects that have a progress bar and are scanned in increments.
   int progress_bar_;
   // Assuming the initial allocation on a page is sequential,
   // 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.
   int available_in_small_free_list_;
   int available_in_medium_free_list_;
   int available_in_large_free_list_;
   int available_in_huge_free_list_;
   int non_available_small_blocks_;
 
   static MemoryChunk* Initialize(Heap* heap, Address base, size_t size,
@@ skipping 2197 matching lines @@
     count = 0;
   }
   // Must be small, since an iteration is used for lookup.
   static const int kMaxComments = 64;
 };
 #endif
 }
 }  // namespace v8::internal
 
 #endif  // V8_HEAP_SPACES_H_