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The Tor Browser
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sequence_token.h (4228B)

      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 #include "base/auto_reset.h"
      9 #include "base/base_export.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  constexpr 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  constexpr 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
     97    [[maybe_unused, nodiscard]] ScopedSetSequenceTokenForCurrentThread {
     98 public:
     99  // Throughout the lifetime of the constructed object,
    100  // SequenceToken::GetForCurrentThread() will return |sequence_token| and
    101  // TaskToken::GetForCurrentThread() will return a TaskToken which is not equal
    102  // to any TaskToken returned in the scope of another
    103  // ScopedSetSequenceTokenForCurrentThread.
    104  explicit ScopedSetSequenceTokenForCurrentThread(
    105      const SequenceToken& sequence_token);
    106  ScopedSetSequenceTokenForCurrentThread(
    107      const ScopedSetSequenceTokenForCurrentThread&) = delete;
    108  ScopedSetSequenceTokenForCurrentThread& operator=(
    109      const ScopedSetSequenceTokenForCurrentThread&) = delete;
    110  ~ScopedSetSequenceTokenForCurrentThread();
    111 
    112 private:
    113  const AutoReset<SequenceToken> sequence_token_resetter_;
    114  const AutoReset<TaskToken> task_token_resetter_;
    115 };
    116 
    117 }  // namespace base
    118 
    119 #endif  // BASE_SEQUENCE_TOKEN_H_