Reland "[heap] Fine-grained JSArrayBuffer tracking"

src/heap/array-buffer-tracker.h

Index: src/heap/array-buffer-tracker.h
diff --git a/src/heap/array-buffer-tracker.h b/src/heap/array-buffer-tracker.h
index 6130003d15263fff94d56070d44a4713858ab9da..293496b44b97b4ba37b202a142b112b171dd86d0 100644
--- a/src/heap/array-buffer-tracker.h
+++ b/src/heap/array-buffer-tracker.h
@@ -7,69 +7,83 @@
 
 #include <map>
 
+#include "src/allocation.h"
 #include "src/base/platform/mutex.h"
 #include "src/globals.h"
 
 namespace v8 {
 namespace internal {
 
-// Forward declarations.
 class Heap;
+class Page;

[Hannes Payer (out of office), 2016/06/01 13:44:17]

Alphabetic order

[Michael Lippautz, 2016/06/01 14:19:19]

Done.

 class JSArrayBuffer;
 
-class ArrayBufferTracker {
+class ArrayBufferTracker : public AllStatic {
  public:
-  explicit ArrayBufferTracker(Heap* heap) : heap_(heap) {}
-  ~ArrayBufferTracker();
-
-  inline Heap* heap() { return heap_; }
+  enum ProcessingMode {
+    kUpdateForwardedRemoveOthers,
+    kUpdateForwardedKeepOthers,
+  };
 
   // The following methods are used to track raw C++ pointers to externally
   // allocated memory used as backing store in live array buffers.
 
-  // A new ArrayBuffer was created with |data| as backing store.
-  void RegisterNew(JSArrayBuffer* buffer);
+  // Register/unregister a new JSArrayBuffer |buffer| for tracking.
+  static void RegisterNew(Heap* heap, JSArrayBuffer* buffer);
+  static void Unregister(Heap* heap, JSArrayBuffer* buffer);
 
-  // The backing store |data| is no longer owned by V8.
-  void Unregister(JSArrayBuffer* buffer);
+  // Frees all backing store pointers for dead JSArrayBuffers in new space.
+  static void FreeDeadInNewSpace(Heap* heap);
 
-  // A live ArrayBuffer was discovered during marking/scavenge.
-  void MarkLive(JSArrayBuffer* buffer);
+  static void FreeDead(Page* page);

[Hannes Payer (out of office), 2016/06/01 13:44:17]

All these nice methods had comments in that class, let's add some descriptions.

[Michael Lippautz, 2016/06/01 14:19:19]

Done.

 
-  // Frees all backing store pointers that weren't discovered in the previous
-  // marking or scavenge phase.
-  void FreeDead(bool from_scavenge);
+  static void ProcessBuffers(Page* page, ProcessingMode mode);
 
-  // Prepare for a new scavenge phase. A new marking phase is implicitly
-  // prepared by finishing the previous one.
-  void PrepareDiscoveryInNewSpace();
+  static bool IsTracked(JSArrayBuffer* buffer);
+};
 
-  // An ArrayBuffer moved from new space to old space.
-  void Promote(JSArrayBuffer* buffer);
+// LocalArrayBufferTracker tracks internalized array buffers.
+//
+//  Never call directly but instead always call through |ArrayBufferTracker|.
+class LocalArrayBufferTracker {
+ public:
+  typedef std::pair<void*, size_t> Value;
+  typedef JSArrayBuffer* Key;
 
- private:
-  base::Mutex mutex_;
-  Heap* heap_;
+  enum CallbackResult { kKeepEntry, kUpdateEntry, kRemoveEntry };
 
-  // |live_array_buffers_| maps externally allocated memory used as backing
-  // store for ArrayBuffers to the length of the respective memory blocks.
-  //
-  // At the beginning of mark/compact, |not_yet_discovered_array_buffers_| is
-  // a copy of |live_array_buffers_| and we remove pointers as we discover live
-  // ArrayBuffer objects during marking. At the end of mark/compact, the
-  // remaining memory blocks can be freed.
-  std::map<void*, size_t> live_array_buffers_;
-  std::map<void*, size_t> not_yet_discovered_array_buffers_;
-
-  // To be able to free memory held by ArrayBuffers during scavenge as well, we
-  // have a separate list of allocated memory held by ArrayBuffers in new space.
+  explicit LocalArrayBufferTracker(Heap* heap) : heap_(heap) {}
+  ~LocalArrayBufferTracker();
+
+  void Add(Key key, const Value& value);
+  Value Remove(Key key);
+
+  // Frees up any buffers that are currently not marked.
+  void FreeDead();
+
+  // Processes buffers one by one. The CallbackResult of the callback decides
+  // what action to take on the buffer.
   //
-  // Since mark/compact also evacuates the new space, all pointers in the
-  // |live_array_buffers_for_scavenge_| list are also in the
-  // |live_array_buffers_| list.
-  std::map<void*, size_t> live_array_buffers_for_scavenge_;
-  std::map<void*, size_t> not_yet_discovered_array_buffers_for_scavenge_;
+  // Callback should be of type:
+  //   CallbackResult fn(JSArrayBuffer* buffer, JSArrayBuffer** new_buffer);
+  template <typename Callback>
+  inline void Process(Callback callback);
+
+  bool IsEmpty() { return array_buffers_.empty(); }
+
+  bool IsTracked(Key key) {
+    return array_buffers_.find(key) != array_buffers_.end();
+  }
+
+ private:
+  // TODO(mlippautz): Switch to unordered_map once it is supported on all
+  // platforms.
+  typedef std::map<Key, Value> TrackingMap;
+
+  Heap* heap_;
+  TrackingMap array_buffers_;
 };
+
 }  // namespace internal
 }  // namespace v8
 #endif  // V8_HEAP_ARRAY_BUFFER_TRACKER_H_