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 // Apart from debug builds, we also enable the thread checker in 9 // builds with DCHECK_ALWAYS_ON so that trybots and waterfall bots 10 // with this define will get the same level of thread checking as 11 // debug bots. 12 // 13 // Note that this does not perfectly match situations where DCHECK is 14 // enabled. For example a non-official release build may have 15 // DCHECK_ALWAYS_ON undefined (and therefore ThreadChecker would be 16 // disabled) but have DCHECKs enabled at runtime. 17 #if (!defined(NDEBUG) || defined(DCHECK_ALWAYS_ON)) 18 #define ENABLE_THREAD_CHECKER 1 19 #else 20 #define ENABLE_THREAD_CHECKER 0 21 #endif 22 23 #include "base/threading/thread_checker_impl.h" 24 25 namespace base { 26 27 // Do nothing implementation, for use in release mode. 28 // 29 // Note: You should almost always use the ThreadChecker class to get the 30 // right version for your build configuration. 31 class ThreadCheckerDoNothing { 32 public: 33 bool CalledOnValidThread() const { 34 return true; 35 } 36 37 void DetachFromThread() {} 38 }; 39 40 // ThreadChecker is a helper class used to help verify that some methods of a 41 // class are called from the same thread. It provides identical functionality to 42 // base::NonThreadSafe, but it is meant to be held as a member variable, rather 43 // than inherited from base::NonThreadSafe. 44 // 45 // While inheriting from base::NonThreadSafe may give a clear indication about 46 // the thread-safety of a class, it may also lead to violations of the style 47 // guide with regard to multiple inheritance. The choice between having a 48 // ThreadChecker member and inheriting from base::NonThreadSafe should be based 49 // on whether: 50 // - Derived classes need to know the thread they belong to, as opposed to 51 // having that functionality fully encapsulated in the base class. 52 // - Derived classes should be able to reassign the base class to another 53 // thread, via DetachFromThread. 54 // 55 // If neither of these are true, then having a ThreadChecker member and calling 56 // CalledOnValidThread is the preferable solution. 57 // 58 // Example: 59 // class MyClass { 60 // public: 61 // void Foo() { 62 // DCHECK(thread_checker_.CalledOnValidThread()); 63 // ... (do stuff) ... 64 // } 65 // 66 // private: 67 // ThreadChecker thread_checker_; 68 // } 69 // 70 // In Release mode, CalledOnValidThread will always return true. 71 #if ENABLE_THREAD_CHECKER 72 class ThreadChecker : public ThreadCheckerImpl { 73 }; 74 #else 75 class ThreadChecker : public ThreadCheckerDoNothing { 76 }; 77 #endif // ENABLE_THREAD_CHECKER 78 79 #undef ENABLE_THREAD_CHECKER 80 81 } // namespace base 82 83 #endif // BASE_THREADING_THREAD_CHECKER_H_ 84
