Revert "Delete CC."

cc/base/blocking_task_runner.h

+// Copyright 2013 The Chromium 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 CC_BASE_BLOCKING_TASK_RUNNER_H_
+#define CC_BASE_BLOCKING_TASK_RUNNER_H_
+
+#include <vector>
+
+#include "base/location.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/single_thread_task_runner.h"
+#include "base/synchronization/lock.h"
+#include "base/threading/platform_thread.h"
+
+namespace cc {
+
+// This class wraps a SingleThreadTaskRunner but allows posted tasks to be
+// run without a round trip through the message loop. This shortcutting
+// removes guarantees about ordering. Tasks posted while the
+// BlockingTaskRunner is in a capturing state will run in order, and tasks
+// posted while the BlockingTaskRunner is /not/ in a capturing state will
+// run in order, but the two sets of tasks will *not* run in order relative
+// to when they were posted.
+//
+// To use this class, post tasks to the task runner returned by
+// BlockingTaskRunner::Create(). The thread it is created on identifies the
+// thread you want the tasks to run on. The SingleThreadTaskRunner which is
+// passed into Create() is used to run tasks that are posted when not in a
+// capturing state.
+//
+// Then, on the thread that the given task runner belongs to, you may
+// instantiate a BlockingTaskRunner::CapturePostTasks. While this object
+// exists, the task runner will collect any PostTasks called on it, posting
+// tasks to that thread from anywhere. This CapturePostTasks object provides
+// a window in time where tasks can shortcut past the MessageLoop. As soon
+// as the CapturePostTasks object is destroyed (goes out of scope), all
+// tasks that had been posted to the thread during the window will be executed
+// immediately.
+//
+// Beware of re-entrancy, make sure the CapturePostTasks object is destroyed at
+// a time when it makes sense for the embedder to call arbitrary things.
+class BlockingTaskRunner {
+ public:
+  // Creates a BlockingTaskRunner for a given SingleThreadTaskRunner.
+  // |task_runner| will be used to run the tasks which are posted while we are
+  // not capturing. |task_runner| should belong to same the thread on which
+  // capturing is done.
+  static scoped_ptr<BlockingTaskRunner> Create(
+      scoped_refptr<base::SingleThreadTaskRunner> task_runner);
+
+  ~BlockingTaskRunner();
+
+  // While an object of this type is held alive on a thread, any tasks
+  // posted to the thread will be captured and run as soon as the object
+  // is destroyed, shortcutting past the task runner.
+  class CapturePostTasks {
+   public:
+    explicit CapturePostTasks(BlockingTaskRunner* blocking_runner);
+    ~CapturePostTasks();
+
+   private:
+    BlockingTaskRunner* blocking_runner_;
+
+    DISALLOW_COPY_AND_ASSIGN(CapturePostTasks);
+  };
+
+  // True if tasks posted to the BlockingTaskRunner will run on the current
+  // thread.
+  bool BelongsToCurrentThread();
+
+  // Posts a task using the contained SingleThreadTaskRunner unless |capture_|
+  // is true. When |capture_| is true, tasks posted will be caught and stored
+  // until the capturing stops. At that time the tasks will be run directly
+  // instead of being posted to the SingleThreadTaskRunner.
+  bool PostTask(const tracked_objects::Location& from_here,
+                const base::Closure& task);
+
+ private:
+  explicit BlockingTaskRunner(
+      scoped_refptr<base::SingleThreadTaskRunner> task_runner);
+
+  void SetCapture(bool capture);
+
+  base::PlatformThreadId thread_id_;
+  scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
+
+  base::Lock lock_;
+  int capture_;
+  std::vector<base::Closure> captured_tasks_;
+
+  DISALLOW_COPY_AND_ASSIGN(BlockingTaskRunner);
+};
+
+}  // namespace cc
+
+#endif  // CC_BASE_BLOCKING_TASK_RUNNER_H_