1 // Copyright (c) 2012 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 BASE_THREADING_THREAD_CHECKER_H_ 6 #define BASE_THREADING_THREAD_CHECKER_H_ 7 8 #include "base/logging.h" 9 #include "base/threading/thread_checker_impl.h" 10 11 namespace base { 12 13 // Do nothing implementation, for use in release mode. 14 // 15 // Note: You should almost always use the ThreadChecker class to get the 16 // right version for your build configuration. 17 class ThreadCheckerDoNothing { 18 public: 19 bool CalledOnValidThread() const WARN_UNUSED_RESULT { 20 return true; 21 } 22 23 void DetachFromThread() {} 24 }; 25 26 // ThreadChecker is a helper class used to help verify that some methods of a 27 // class are called from the same thread. It provides identical functionality to 28 // base::NonThreadSafe, but it is meant to be held as a member variable, rather 29 // than inherited from base::NonThreadSafe. 30 // 31 // While inheriting from base::NonThreadSafe may give a clear indication about 32 // the thread-safety of a class, it may also lead to violations of the style 33 // guide with regard to multiple inheritance. The choice between having a 34 // ThreadChecker member and inheriting from base::NonThreadSafe should be based 35 // on whether: 36 // - Derived classes need to know the thread they belong to, as opposed to 37 // having that functionality fully encapsulated in the base class. 38 // - Derived classes should be able to reassign the base class to another 39 // thread, via DetachFromThread. 40 // 41 // If neither of these are true, then having a ThreadChecker member and calling 42 // CalledOnValidThread is the preferable solution. 43 // 44 // Example: 45 // class MyClass { 46 // public: 47 // void Foo() { 48 // DCHECK(thread_checker_.CalledOnValidThread()); 49 // ... (do stuff) ... 50 // } 51 // 52 // private: 53 // ThreadChecker thread_checker_; 54 // } 55 // 56 // Note that, when enabled, CalledOnValidThread() returns false when called from 57 // tasks posted to SingleThreadTaskRunners bound to different sequences, even if 58 // the tasks happen to run on the same thread (e.g. two independent TaskRunners 59 // with ExecutionMode::SINGLE_THREADED on the TaskScheduler that happen to share 60 // a thread). 61 // 62 // In Release mode, CalledOnValidThread will always return true. 63 #if DCHECK_IS_ON() 64 class ThreadChecker : public ThreadCheckerImpl { 65 }; 66 #else 67 class ThreadChecker : public ThreadCheckerDoNothing { 68 }; 69 #endif // DCHECK_IS_ON() 70 71 } // namespace base 72 73 #endif // BASE_THREADING_THREAD_CHECKER_H_ 74
