1 // Copyright 2012 The Chromium Authors 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_SEQUENCE_CHECKER_H_ 6 #define BASE_SEQUENCE_CHECKER_H_ 7 8 #include "base/base_export.h" 9 #include "base/dcheck_is_on.h" 10 #include "base/macros/uniquify.h" 11 #include "base/sequence_checker_impl.h" 12 13 // SequenceChecker is a helper class used to help verify that some methods of a 14 // class are called sequentially (for thread-safety). It supports thread safety 15 // annotations (see base/thread_annotations.h). 16 // 17 // Use the macros below instead of the SequenceChecker directly so that the 18 // unused member doesn't result in an extra byte (four when padded) per 19 // instance in production. 20 // 21 // This class is much prefered to ThreadChecker for thread-safety checks. 22 // ThreadChecker should only be used for classes that are truly thread-affine 23 // (use thread-local-storage or a third-party API that does). 24 // 25 // Debugging: 26 // If SequenceChecker::EnableStackLogging() is called beforehand, then when 27 // SequenceChecker fails, in addition to crashing with a stack trace of where 28 // the violation occurred, it will also dump a stack trace of where the 29 // checker was bound to a sequence. 30 // 31 // Usage: 32 // class MyClass { 33 // public: 34 // MyClass() { 35 // // Detaching on construction is necessary for objects that are 36 // // constructed on one sequence and forever after used from another 37 // // sequence. 38 // DETACH_FROM_SEQUENCE(my_sequence_checker_); 39 // } 40 // 41 // ~MyClass() { 42 // // SequenceChecker doesn't automatically check it's destroyed on origin 43 // // sequence for the same reason it's sometimes detached in the 44 // // constructor. It's okay to destroy off sequence if the owner 45 // // otherwise knows usage on the associated sequence is done. If you're 46 // // not detaching in the constructor, you probably want to explicitly 47 // // check in the destructor. 48 // DCHECK_CALLED_ON_VALID_SEQUENCE(my_sequence_checker_); 49 // } 50 // void MyMethod() { 51 // DCHECK_CALLED_ON_VALID_SEQUENCE(my_sequence_checker_); 52 // ... (do stuff) ... 53 // MyOtherMethod(); 54 // } 55 // 56 // void MyOtherMethod() 57 // VALID_CONTEXT_REQUIRED(my_sequence_checker_) { 58 // foo_ = 42; 59 // } 60 // 61 // private: 62 // // GUARDED_BY_CONTEXT() enforces that this member is only 63 // // accessed from a scope that invokes DCHECK_CALLED_ON_VALID_SEQUENCE() 64 // // or from a function annotated with VALID_CONTEXT_REQUIRED(). A 65 // // DCHECK build will not compile if the member is accessed and these 66 // // conditions are not met. 67 // int foo_ GUARDED_BY_CONTEXT(my_sequence_checker_); 68 // 69 // SEQUENCE_CHECKER(my_sequence_checker_); 70 // } 71 72 #if DCHECK_IS_ON() 73 #define SEQUENCE_CHECKER(name) base::SequenceChecker name 74 #define DCHECK_CALLED_ON_VALID_SEQUENCE(name, ...) \ 75 base::ScopedValidateSequenceChecker BASE_UNIQUIFY( \ 76 scoped_validate_sequence_checker_)(name, ##__VA_ARGS__) 77 #define DETACH_FROM_SEQUENCE(name) (name).DetachFromSequence() 78 #else // DCHECK_IS_ON() 79 // A no-op expansion that can be followed by a semicolon at class level. 80 #define SEQUENCE_CHECKER(name) static_assert(true, "") 81 #define DCHECK_CALLED_ON_VALID_SEQUENCE(name, ...) EAT_CHECK_STREAM_PARAMS() 82 #define DETACH_FROM_SEQUENCE(name) 83 #endif // DCHECK_IS_ON() 84 85 namespace base { 86 87 // Do nothing implementation, for use in release mode. 88 // 89 // Note: You should almost always use the SequenceChecker class (through the 90 // above macros) to get the right version for your build configuration. 91 // Note: This is marked with "context" capability in order to support 92 // thread_annotations.h. 93 class THREAD_ANNOTATION_ATTRIBUTE__(capability("context")) 94 SequenceCheckerDoNothing { 95 public: EnableStackLogging()96 static void EnableStackLogging() {} 97 98 SequenceCheckerDoNothing() = default; 99 100 // Moving between matching sequences is allowed to help classes with 101 // SequenceCheckers that want a default move-construct/assign. 102 SequenceCheckerDoNothing(SequenceCheckerDoNothing&& other) = default; 103 SequenceCheckerDoNothing& operator=(SequenceCheckerDoNothing&& other) = 104 default; 105 SequenceCheckerDoNothing(const SequenceCheckerDoNothing&) = delete; 106 SequenceCheckerDoNothing& operator=(const SequenceCheckerDoNothing&) = delete; 107 108 [[nodiscard]] bool CalledOnValidSequence(void* = nullptr) const { 109 return true; 110 } DetachFromSequence()111 void DetachFromSequence() {} 112 }; 113 114 #if DCHECK_IS_ON() 115 using SequenceChecker = SequenceCheckerImpl; 116 #else 117 using SequenceChecker = SequenceCheckerDoNothing; 118 #endif // DCHECK_IS_ON() 119 120 #if DCHECK_IS_ON() 121 class BASE_EXPORT SCOPED_LOCKABLE ScopedValidateSequenceChecker { 122 public: 123 explicit ScopedValidateSequenceChecker(const SequenceChecker& checker) 124 EXCLUSIVE_LOCK_FUNCTION(checker); 125 ~ScopedValidateSequenceChecker() UNLOCK_FUNCTION(); 126 }; 127 #endif 128 129 } // namespace base 130 131 #endif // BASE_SEQUENCE_CHECKER_H_ 132