base/synchronization/cancellation_flag.h

   1 // Copyright (c) 2011 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_SYNCHRONIZATION_CANCELLATION_FLAG_H_
   6 #define BASE_SYNCHRONIZATION_CANCELLATION_FLAG_H_
   7
   8 #include "base/base_export.h"
   9 #include "base/atomicops.h"
  10 #include "base/threading/platform_thread.h"
  11
  12 namespace base {
  13
  14 // CancellationFlag allows one thread to cancel jobs executed on some worker
  15 // thread. Calling Set() from one thread and IsSet() from a number of threads
  16 // is thread-safe.
  17 //
  18 // This class IS NOT intended for synchronization between threads.
  19 class BASE_EXPORT CancellationFlag {
  20  public:
  21   CancellationFlag() : flag_(false) {
  22 #if !defined(NDEBUG)
  23     set_on_ = PlatformThread::CurrentId();
  24 #endif
  25   }
  26   ~CancellationFlag() {}
  27
  28   // Set the flag. May only be called on the thread which owns the object.
  29   void Set();
  30   bool IsSet() const;  // Returns true iff the flag was set.
  31
  32   // For subtle reasons that may be different on different architectures,
  33   // a different thread testing IsSet() may erroneously read 'true' after
  34   // this method has been called.
  35   void UnsafeResetForTesting();
  36
  37  private:
  38   base::subtle::Atomic32 flag_;
  39 #if !defined(NDEBUG)
  40   PlatformThreadId set_on_;
  41 #endif
  42
  43   DISALLOW_COPY_AND_ASSIGN(CancellationFlag);
  44 };
  45
  46 }  // namespace base
  47
  48 #endif  // BASE_SYNCHRONIZATION_CANCELLATION_FLAG_H_