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      1 // Copyright 2016 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_SEQUENCE_TOKEN_H_
      6 #define BASE_SEQUENCE_TOKEN_H_
      7 
      8 #include "base/base_export.h"
      9 #include "base/macros.h"
     10 
     11 namespace base {
     12 
     13 // A token that identifies a series of sequenced tasks (i.e. tasks that run one
     14 // at a time in posting order).
     15 class BASE_EXPORT SequenceToken {
     16  public:
     17   // Instantiates an invalid SequenceToken.
     18   SequenceToken() = default;
     19 
     20   // Explicitly allow copy.
     21   SequenceToken(const SequenceToken& other) = default;
     22   SequenceToken& operator=(const SequenceToken& other) = default;
     23 
     24   // An invalid SequenceToken is not equal to any other SequenceToken, including
     25   // other invalid SequenceTokens.
     26   bool operator==(const SequenceToken& other) const;
     27   bool operator!=(const SequenceToken& other) const;
     28 
     29   // Returns true if this is a valid SequenceToken.
     30   bool IsValid() const;
     31 
     32   // Returns the integer uniquely representing this SequenceToken. This method
     33   // should only be used for tracing and debugging.
     34   int ToInternalValue() const;
     35 
     36   // Returns a valid SequenceToken which isn't equal to any previously returned
     37   // SequenceToken.
     38   static SequenceToken Create();
     39 
     40   // Returns the SequenceToken associated with the task running on the current
     41   // thread, as determined by the active ScopedSetSequenceTokenForCurrentThread
     42   // if any.
     43   static SequenceToken GetForCurrentThread();
     44 
     45  private:
     46   explicit SequenceToken(int token) : token_(token) {}
     47 
     48   static constexpr int kInvalidSequenceToken = -1;
     49   int token_ = kInvalidSequenceToken;
     50 };
     51 
     52 // A token that identifies a task.
     53 //
     54 // This is used by ThreadCheckerImpl to determine whether calls to
     55 // CalledOnValidThread() come from the same task and hence are deterministically
     56 // single-threaded (vs. calls coming from different sequenced or parallel tasks,
     57 // which may or may not run on the same thread).
     58 class BASE_EXPORT TaskToken {
     59  public:
     60   // Instantiates an invalid TaskToken.
     61   TaskToken() = default;
     62 
     63   // Explicitly allow copy.
     64   TaskToken(const TaskToken& other) = default;
     65   TaskToken& operator=(const TaskToken& other) = default;
     66 
     67   // An invalid TaskToken is not equal to any other TaskToken, including
     68   // other invalid TaskTokens.
     69   bool operator==(const TaskToken& other) const;
     70   bool operator!=(const TaskToken& other) const;
     71 
     72   // Returns true if this is a valid TaskToken.
     73   bool IsValid() const;
     74 
     75   // In the scope of a ScopedSetSequenceTokenForCurrentThread, returns a valid
     76   // TaskToken which isn't equal to any TaskToken returned in the scope of a
     77   // different ScopedSetSequenceTokenForCurrentThread. Otherwise, returns an
     78   // invalid TaskToken.
     79   static TaskToken GetForCurrentThread();
     80 
     81  private:
     82   friend class ScopedSetSequenceTokenForCurrentThread;
     83 
     84   explicit TaskToken(int token) : token_(token) {}
     85 
     86   // Returns a valid TaskToken which isn't equal to any previously returned
     87   // TaskToken. This is private as it only meant to be instantiated by
     88   // ScopedSetSequenceTokenForCurrentThread.
     89   static TaskToken Create();
     90 
     91   static constexpr int kInvalidTaskToken = -1;
     92   int token_ = kInvalidTaskToken;
     93 };
     94 
     95 // Instantiate this in the scope where a single task runs.
     96 class BASE_EXPORT ScopedSetSequenceTokenForCurrentThread {
     97  public:
     98   // Throughout the lifetime of the constructed object,
     99   // SequenceToken::GetForCurrentThread() will return |sequence_token| and
    100   // TaskToken::GetForCurrentThread() will return a TaskToken which is not equal
    101   // to any TaskToken returned in the scope of another
    102   // ScopedSetSequenceTokenForCurrentThread.
    103   ScopedSetSequenceTokenForCurrentThread(const SequenceToken& sequence_token);
    104   ~ScopedSetSequenceTokenForCurrentThread();
    105 
    106  private:
    107   const SequenceToken sequence_token_;
    108   const TaskToken task_token_;
    109 
    110   DISALLOW_COPY_AND_ASSIGN(ScopedSetSequenceTokenForCurrentThread);
    111 };
    112 
    113 }  // namespace base
    114 
    115 #endif  // BASE_SEQUENCE_TOKEN_H_
    116