1 // Copyright 2013 The Chromium Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 5 #ifndef CC_TREES_BLOCKING_TASK_RUNNER_H_ 6 #define CC_TREES_BLOCKING_TASK_RUNNER_H_ 7 8 #include <vector> 9 10 #include "base/location.h" 11 #include "base/memory/scoped_ptr.h" 12 #include "base/single_thread_task_runner.h" 13 #include "base/synchronization/lock.h" 14 #include "base/threading/platform_thread.h" 15 #include "cc/base/cc_export.h" 16 17 namespace cc { 18 19 // This class wraps a SingleThreadTaskRunner but allows posted tasks to be 20 // run without a round trip through the message loop. This shortcutting 21 // removes guarantees about ordering. Tasks posted while the 22 // BlockingTaskRunner is in a capturing state will run in order, and tasks 23 // posted while the BlockingTaskRunner is /not/ in a capturing state will 24 // run in order, but the two sets of tasks will *not* run in order relative 25 // to when they were posted. 26 // 27 // To use this class, post tasks to the task runner returned by 28 // BlockingTaskRunner::Create(). The thread it is created on identifies the 29 // thread you want the tasks to run on. The SingleThreadTaskRunner which is 30 // passed into Create() is used to run tasks that are posted when not in a 31 // capturing state. 32 // 33 // Then, on the thread that the given task runner belongs to, you may 34 // instantiate a BlockingTaskRunner::CapturePostTasks. While this object 35 // exists, the task runner will collect any PostTasks called on it, posting 36 // tasks to that thread from anywhere. This CapturePostTasks object provides 37 // a window in time where tasks can shortcut past the MessageLoop. As soon 38 // as the CapturePostTasks object is destroyed (goes out of scope), all 39 // tasks that had been posted to the thread during the window will be executed 40 // immediately. 41 // 42 // Beware of re-entrancy, make sure the CapturePostTasks object is destroyed at 43 // a time when it makes sense for the embedder to call arbitrary things. 44 class CC_EXPORT BlockingTaskRunner { 45 public: 46 // Creates a BlockingTaskRunner for a given SingleThreadTaskRunner. 47 // |task_runner| will be used to run the tasks which are posted while we are 48 // not capturing. |task_runner| should belong to same the thread on which 49 // capturing is done. 50 static scoped_ptr<BlockingTaskRunner> Create( 51 scoped_refptr<base::SingleThreadTaskRunner> task_runner); 52 53 ~BlockingTaskRunner(); 54 55 // While an object of this type is held alive on a thread, any tasks 56 // posted to the thread will be captured and run as soon as the object 57 // is destroyed, shortcutting past the task runner. 58 class CC_EXPORT CapturePostTasks { 59 public: 60 explicit CapturePostTasks(BlockingTaskRunner* blocking_runner); 61 ~CapturePostTasks(); 62 63 private: 64 BlockingTaskRunner* blocking_runner_; 65 66 DISALLOW_COPY_AND_ASSIGN(CapturePostTasks); 67 }; 68 69 // True if tasks posted to the BlockingTaskRunner will run on the current 70 // thread. 71 bool BelongsToCurrentThread(); 72 73 // Posts a task using the contained SingleThreadTaskRunner unless |capture_| 74 // is true. When |capture_| is true, tasks posted will be caught and stored 75 // until the capturing stops. At that time the tasks will be run directly 76 // instead of being posted to the SingleThreadTaskRunner. 77 bool PostTask(const tracked_objects::Location& from_here, 78 const base::Closure& task); 79 80 private: 81 explicit BlockingTaskRunner( 82 scoped_refptr<base::SingleThreadTaskRunner> task_runner); 83 84 void SetCapture(bool capture); 85 86 base::PlatformThreadId thread_id_; 87 scoped_refptr<base::SingleThreadTaskRunner> task_runner_; 88 89 base::Lock lock_; 90 int capture_; 91 std::vector<base::Closure> captured_tasks_; 92 93 DISALLOW_COPY_AND_ASSIGN(BlockingTaskRunner); 94 }; 95 96 } // namespace cc 97 98 #endif // CC_TREES_BLOCKING_TASK_RUNNER_H_ 99
