components/scheduler/child/pollable_thread_safe_flag.h

   1 // Copyright 2015 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 COMPONENTS_SCHEDULER_CHILD_POLLABLE_THREAD_SAFE_FLAG_H_
   6 #define COMPONENTS_SCHEDULER_CHILD_POLLABLE_THREAD_SAFE_FLAG_H_
   7
   8 #include "base/atomicops.h"
   9 #include "base/synchronization/lock.h"
  10
  11 // A PollableThreadSafeFlag can be polled without requiring a lock, but can only
  12 // be updated if a lock is held. This enables lock-free checking as to whether a
  13 // condition has changed, while protecting operations which update the condition
  14 // with a lock. You must ensure that the flag is only updated within the same
  15 // lock-protected critical section as any other variables on which the condition
  16 // depends.
  17 class PollableThreadSafeFlag {
  18  public:
  19   explicit PollableThreadSafeFlag(base::Lock* write_lock);
  20   ~PollableThreadSafeFlag();
  21
  22   // Set the flag. May only be called if |write_lock| is held.
  23   void SetWhileLocked(bool value);
  24
  25   // Returns true iff the flag is set to true.
  26   bool IsSet() const;
  27
  28  private:
  29   base::subtle::Atomic32 flag_;
  30   base::Lock* write_lock_;  // Not owned.
  31
  32   DISALLOW_COPY_AND_ASSIGN(PollableThreadSafeFlag);
  33 };
  34
  35 #endif  // COMPONENTS_SCHEDULER_CHILD_POLLABLE_THREAD_SAFE_FLAG_H_