[heap] Implement concurrent marking boilerplate.

src/heap/concurrent-marking.h

+// Copyright 2017 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_CONCURRENT_MARKING_
+#define V8_HEAP_CONCURRENT_MARKING_
+
+#include "src/allocation.h"
+#include "src/cancelable-task.h"
+#include "src/locked-queue.h"
+#include "src/utils.h"
+#include "src/v8.h"
+
+namespace v8 {
+namespace internal {
+
+class Heap;
+class Isolate;
+
+class ConcurrentMarking {
+ public:
+  static const int kMaxNumberOfTasks = 10;

[Hannes Payer (out of office), 2017/03/06 13:43:19]

Instead of using a max, let's add a heuristic function that returns an
appropriate number. Similar to parallel compaction.

Maybe, the default should be 1.

[ulan, 2017/03/06 13:52:19]

It's the upper bound on number of tasks. The actual number of tasks will be set
dynamically in StartMarkingTasks. We can start there with 1 or use heuristic.

+
+  explicit ConcurrentMarking(Heap* heap);
+  ~ConcurrentMarking();
+
+  void EnqueueObject(HeapObject* object);
+  bool IsQueueEmpty();
+
+  void StartMarkingTasks(int number_of_tasks);
+  void WaitForTasksToComplete();
+
+ private:
+  class Task;
+  // TODO(ulan): Replace with faster queue.
+  typedef LockedQueue<HeapObject*> Queue;
+
+  Heap* heap_;
+  base::Semaphore pending_tasks_;
+  Queue queue_;
+  int number_of_tasks_;
+  uint32_t task_ids_[kMaxNumberOfTasks];
+};
+
+}  // namespace internal
+}  // namespace v8
+
+#endif  // V8_HEAP_PAGE_PARALLEL_JOB_