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/ref_counted.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::current() on the thread you want the tasks to run. 29 // Hold a reference to the BlockingTaskRunner as long as you intend to 30 // post tasks to it. 31 // 32 // Then, on the thread from which the BlockingTaskRunner was created, you 33 // may instantiate a BlockingTaskRunner::CapturePostTasks. While this object 34 // exists, the task runner will collect any PostTasks called on it, posting 35 // tasks to that thread from anywhere. This CapturePostTasks object provides 36 // a window in time where tasks can shortcut past the MessageLoop. As soon 37 // as the CapturePostTasks object is destroyed (goes out of scope), all 38 // tasks that had been posted to the thread during the window will be exectuted 39 // immediately. 40 // 41 // Beware of re-entrancy, make sure the CapturePostTasks object is destroyed at 42 // a time when it makes sense for the embedder to call arbitrary things. 43 class CC_EXPORT BlockingTaskRunner 44 : public base::RefCountedThreadSafe<BlockingTaskRunner> { 45 public: 46 // Returns the BlockingTaskRunner for the current thread, creating one if 47 // necessary. 48 static scoped_refptr<BlockingTaskRunner> current(); 49 50 // While an object of this type is held alive on a thread, any tasks 51 // posted to the thread will be captured and run as soon as the object 52 // is destroyed, shortcutting past the MessageLoop. 53 class CC_EXPORT CapturePostTasks { 54 public: 55 CapturePostTasks(); 56 ~CapturePostTasks(); 57 58 private: 59 scoped_refptr<BlockingTaskRunner> blocking_runner_; 60 61 DISALLOW_COPY_AND_ASSIGN(CapturePostTasks); 62 }; 63 64 // True if tasks posted to the BlockingTaskRunner will run on the current 65 // thread. 66 bool BelongsToCurrentThread(); 67 68 // Posts a task using the contained SingleThreadTaskRunner unless |capture_| 69 // is true. When |capture_| is true, tasks posted will be caught and stored 70 // until the capturing stops. At that time the tasks will be run directly 71 // instead of being posted to the SingleThreadTaskRunner. 72 bool PostTask(const tracked_objects::Location& from_here, 73 const base::Closure& task); 74 75 private: 76 friend class base::RefCountedThreadSafe<BlockingTaskRunner>; 77 78 explicit BlockingTaskRunner( 79 scoped_refptr<base::SingleThreadTaskRunner> task_runner); 80 virtual ~BlockingTaskRunner(); 81 82 void SetCapture(bool capture); 83 84 base::PlatformThreadId thread_id_; 85 scoped_refptr<base::SingleThreadTaskRunner> task_runner_; 86 87 base::Lock lock_; 88 int capture_; 89 std::vector<base::Closure> captured_tasks_; 90 }; 91 92 } // namespace cc 93 94 #endif // CC_TREES_BLOCKING_TASK_RUNNER_H_ 95