Reland "[heap] Uncommit marking deque in concurrent task."

src/cancelable-task.h

 // Copyright 2015 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_CANCELABLE_TASK_H_
 #define V8_CANCELABLE_TASK_H_
 
 #include <map>
 
 #include "include/v8-platform.h"
@@ skipping 14 matching lines @@
 class V8_EXPORT_PRIVATE CancelableTaskManager {
  public:
   CancelableTaskManager();
 
   // Registers a new cancelable {task}. Returns the unique {id} of the task that
   // can be used to try to abort a task by calling {Abort}.
   // Must not be called after CancelAndWait.
   uint32_t Register(Cancelable* task);
 
   // Try to abort running a task identified by {id}. The possible outcomes are:
-  // (1) The task is already finished running and thus has been removed from
-  //     the manager.
+  // (1) The task is already finished running or was canceled before and
+  //     thus has been removed from the manager.
   // (2) The task is currently running and cannot be canceled anymore.
   // (3) The task is not yet running (or finished) so it is canceled and
   //     removed.
   //
-  // Returns {false} for (1) and (2), and {true} for (3).
-  bool TryAbort(uint32_t id);
+  enum TryAbortResult { kTaskRemoved, kTaskRunning, kTaskAborted };
+  TryAbortResult TryAbort(uint32_t id);
 
   // Cancels all remaining registered tasks and waits for tasks that are
   // already running. This disallows subsequent Register calls.
   void CancelAndWait();
 
  private:
   // Only called by {Cancelable} destructor. The task is done with executing,
   // but needs to be removed.
   void RemoveFinishedTask(uint32_t id);
 
@@ skipping 110 matching lines @@
  private:
   Isolate* isolate_;
   DISALLOW_COPY_AND_ASSIGN(CancelableIdleTask);
 };
 
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_CANCELABLE_TASK_H_