1 // Copyright 2016 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_TOKEN_H_ 6 #define BASE_SEQUENCE_TOKEN_H_ 7 8 // TODO: Remove this unused include once no other file indirectly depends on it. 9 #include "base/auto_reset.h" 10 #include "base/base_export.h" 11 12 namespace base { 13 namespace internal { 14 15 // A token that identifies a series of sequenced work items (i.e. tasks, native 16 // message handlers, code blocks running outside or a `RunLoop`, etc. that are 17 // mutually exclusive). 18 class BASE_EXPORT SequenceToken { 19 public: 20 // Instantiates an invalid SequenceToken. 21 constexpr SequenceToken() = default; 22 23 // Explicitly allow copy. 24 SequenceToken(const SequenceToken& other) = default; 25 SequenceToken& operator=(const SequenceToken& other) = default; 26 27 // An invalid SequenceToken is not equal to any other SequenceToken, including 28 // other invalid SequenceTokens. 29 bool operator==(const SequenceToken& other) const; 30 bool operator!=(const SequenceToken& other) const; 31 32 // Returns true if this is a valid SequenceToken. 33 bool IsValid() const; 34 35 // Returns the integer uniquely representing this SequenceToken. This method 36 // should only be used for tracing and debugging. 37 int ToInternalValue() const; 38 39 // Returns a valid SequenceToken which isn't equal to any previously returned 40 // SequenceToken. 41 static SequenceToken Create(); 42 43 // Returns the `SequenceToken` for the work item currently running on this 44 // thread. A valid and unique `SequenceToken` is assigned to each thread. It 45 // can be overridden in a scope with `TaskScope`. 46 static SequenceToken GetForCurrentThread(); 47 48 private: SequenceToken(int token)49 explicit SequenceToken(int token) : token_(token) {} 50 51 static constexpr int kInvalidSequenceToken = -1; 52 int token_ = kInvalidSequenceToken; 53 }; 54 55 // A token that identifies a task. 56 // 57 // This is used by ThreadCheckerImpl to determine whether calls to 58 // CalledOnValidThread() come from the same task and hence are deterministically 59 // single-threaded (vs. calls coming from different sequenced or parallel tasks, 60 // which may or may not run on the same thread). 61 class BASE_EXPORT TaskToken { 62 public: 63 // Instantiates an invalid TaskToken. 64 constexpr TaskToken() = default; 65 66 // Explicitly allow copy. 67 TaskToken(const TaskToken& other) = default; 68 TaskToken& operator=(const TaskToken& other) = default; 69 70 // An invalid TaskToken is not equal to any other TaskToken, including 71 // other invalid TaskTokens. 72 bool operator==(const TaskToken& other) const; 73 bool operator!=(const TaskToken& other) const; 74 75 // Returns true if this is a valid TaskToken. 76 bool IsValid() const; 77 78 // In the scope of a `TaskScope`, returns a valid `TaskToken` which isn't 79 // equal to any `TaskToken` returned in the scope of a different `TaskScope`. 80 // Otherwise, returns an invalid `TaskToken`. 81 static TaskToken GetForCurrentThread(); 82 83 private: 84 friend class TaskScope; 85 TaskToken(int token)86 explicit TaskToken(int token) : token_(token) {} 87 88 // Returns a valid `TaskToken` which isn't equal to any previously returned 89 // `TaskToken`. Private as it is only meant to be instantiated by `TaskScope`. 90 static TaskToken Create(); 91 92 static constexpr int kInvalidTaskToken = -1; 93 int token_ = kInvalidTaskToken; 94 }; 95 96 // Returns true if a thread checker bound in a different task than the current 97 // one but on the same sequence and thread may return true from 98 // `CalledOnValidSequence()`. 99 bool BASE_EXPORT CurrentTaskIsThreadBound(); 100 101 // Identifies a scope in which a task runs. 102 class BASE_EXPORT [[maybe_unused, nodiscard]] TaskScope { 103 public: 104 // `sequence_token` identifies the series of mutually exclusive work items 105 // that this task is part of (may be unique if this task isn't mutually 106 // exclusive with any other work item). `is_thread_bound` sets the value 107 // returned by `CurrentTaskIsThreadBound()` within the scope. 108 // `is_running_synchronously` is true iff this is instantiated for a task run 109 // synchronously by `RunOrPostTask()`. 110 explicit TaskScope(SequenceToken sequence_token, 111 bool is_thread_bound, 112 bool is_running_synchronously = false); 113 TaskScope(const TaskScope&) = delete; 114 TaskScope& operator=(const TaskScope&) = delete; 115 ~TaskScope(); 116 117 private: 118 const TaskToken previous_task_token_; 119 const SequenceToken previous_sequence_token_; 120 const bool previous_task_is_thread_bound_; 121 const bool previous_task_is_running_synchronously_; 122 }; 123 124 } // namespace internal 125 126 // Returns true if the current task is run synchronously by `RunOrPostTask()`. 127 bool BASE_EXPORT CurrentTaskIsRunningSynchronously(); 128 129 } // namespace base 130 131 #endif // BASE_SEQUENCE_TOKEN_H_ 132