text: // Copyright (c) 2011 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_SYNCHRONIZATION_CANCELLATION_FLAG_H_
  #define BASE_SYNCHRONIZATION_CANCELLATION_FLAG_H_
  
  #include "base/base_export.h"
  #include "base/atomicops.h"
  #include "base/threading/platform_thread.h"
  
  namespace base {
  
  // CancellationFlag allows one thread to cancel jobs executed on some worker
  // thread. Calling Set() from one thread and IsSet() from a number of threads
  // is thread-safe.
  //
  // This class IS NOT intended for synchronization between threads.
  class BASE_EXPORT CancellationFlag {
   public:
    CancellationFlag() : flag_(false) {
  #if !defined(NDEBUG)
      set_on_ = PlatformThread::CurrentId();
  #endif
    }
    ~CancellationFlag() {}
  
    // Set the flag. May only be called on the thread which owns the object.
    void Set();
    bool IsSet() const;  // Returns true iff the flag was set.
  
    // For subtle reasons that may be different on different architectures,
    // a different thread testing IsSet() may erroneously read 'true' after
    // this method has been called.
    void UnsafeResetForTesting();
  
   private:
    base::subtle::Atomic32 flag_;
  #if !defined(NDEBUG)
    PlatformThreadId set_on_;
  #endif
  
    DISALLOW_COPY_AND_ASSIGN(CancellationFlag);
  };
  
  }  // namespace base
  
  #endif  // BASE_SYNCHRONIZATION_CANCELLATION_FLAG_H_
  