sequence_token.h - mozsearch

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// Copyright 2016 The Chromium Authors. All rights reserved.

// Use of this source code is governed by a BSD-style license that can be

// found in the LICENSE file.

#ifndef BASE_SEQUENCE_TOKEN_H_

#define BASE_SEQUENCE_TOKEN_H_

#include "base/base_export.h"

#include "base/macros.h"

namespace base {

// A token that identifies a series of sequenced tasks (i.e. tasks that run one

// at a time in posting order).

class BASE_EXPORT SequenceToken {

 public:

  // Instantiates an invalid SequenceToken.

  SequenceToken() = default;

  // Explicitly allow copy.

  SequenceToken(const SequenceToken& other) = default;

  SequenceToken& operator=(const SequenceToken& other) = default;

  // An invalid SequenceToken is not equal to any other SequenceToken, including

  // other invalid SequenceTokens.

  bool operator==(const SequenceToken& other) const;

  bool operator!=(const SequenceToken& other) const;

  // Returns true if this is a valid SequenceToken.

  bool IsValid() const;

  // Returns the integer uniquely representing this SequenceToken. This method

  // should only be used for tracing and debugging.

  int ToInternalValue() const;

  // Returns a valid SequenceToken which isn't equal to any previously returned

  // SequenceToken.

  static SequenceToken Create();

  // Returns the SequenceToken associated with the task running on the current

  // thread, as determined by the active ScopedSetSequenceTokenForCurrentThread

  // if any.

  static SequenceToken GetForCurrentThread();

 private:

  explicit SequenceToken(int token) : token_(token) {}

  static constexpr int kInvalidSequenceToken = -1;

  int token_ = kInvalidSequenceToken;

};

// A token that identifies a task.

//

// This is used by ThreadCheckerImpl to determine whether calls to

// CalledOnValidThread() come from the same task and hence are deterministically

// single-threaded (vs. calls coming from different sequenced or parallel tasks,

// which may or may not run on the same thread).

class BASE_EXPORT TaskToken {

 public:

  // Instantiates an invalid TaskToken.

  TaskToken() = default;

  // Explicitly allow copy.

  TaskToken(const TaskToken& other) = default;

  TaskToken& operator=(const TaskToken& other) = default;

  // An invalid TaskToken is not equal to any other TaskToken, including

  // other invalid TaskTokens.

  bool operator==(const TaskToken& other) const;

  bool operator!=(const TaskToken& other) const;

  // Returns true if this is a valid TaskToken.

  bool IsValid() const;

  // In the scope of a ScopedSetSequenceTokenForCurrentThread, returns a valid

  // TaskToken which isn't equal to any TaskToken returned in the scope of a

  // different ScopedSetSequenceTokenForCurrentThread. Otherwise, returns an

  // invalid TaskToken.

  static TaskToken GetForCurrentThread();

 private:

  friend class ScopedSetSequenceTokenForCurrentThread;

  explicit TaskToken(int token) : token_(token) {}

  // Returns a valid TaskToken which isn't equal to any previously returned

  // TaskToken. This is private as it only meant to be instantiated by

  // ScopedSetSequenceTokenForCurrentThread.

  static TaskToken Create();

  static constexpr int kInvalidTaskToken = -1;

  int token_ = kInvalidTaskToken;

};

// Instantiate this in the scope where a single task runs.

class BASE_EXPORT ScopedSetSequenceTokenForCurrentThread {

 public:

  // Throughout the lifetime of the constructed object,

  // SequenceToken::GetForCurrentThread() will return |sequence_token| and

  // TaskToken::GetForCurrentThread() will return a TaskToken which is not equal

  // to any TaskToken returned in the scope of another

  // ScopedSetSequenceTokenForCurrentThread.

  ScopedSetSequenceTokenForCurrentThread(const SequenceToken& sequence_token);

  ~ScopedSetSequenceTokenForCurrentThread();

 private:

  const SequenceToken sequence_token_;

  const TaskToken task_token_;

  DISALLOW_COPY_AND_ASSIGN(ScopedSetSequenceTokenForCurrentThread);

};

}  // namespace base

#endif  // BASE_SEQUENCE_TOKEN_H_