cc/base/completion_event.h

   1 // Copyright 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 CC_BASE_COMPLETION_EVENT_H_
   6 #define CC_BASE_COMPLETION_EVENT_H_
   7
   8 #include "base/logging.h"
   9 #include "base/synchronization/waitable_event.h"
  10 #include "base/threading/thread_restrictions.h"
  11
  12 namespace cc {
  13
  14 // Used for making blocking calls from one thread to another. Use only when
  15 // absolutely certain that doing-so will not lead to a deadlock.
  16 //
  17 // It is safe to destroy this object as soon as Wait() returns.
  18 class CompletionEvent {
  19  public:
  20   CompletionEvent()
  21       : event_(false /* manual_reset */, false /* initially_signaled */) {
  22 #if DCHECK_IS_ON()
  23     waited_ = false;
  24     signaled_ = false;
  25 #endif
  26   }
  27
  28   ~CompletionEvent() {
  29 #if DCHECK_IS_ON()
  30     DCHECK(waited_);
  31     DCHECK(signaled_);
  32 #endif
  33   }
  34
  35   void Wait() {
  36 #if DCHECK_IS_ON()
  37     DCHECK(!waited_);
  38     waited_ = true;
  39 #endif
  40     base::ThreadRestrictions::ScopedAllowWait allow_wait;
  41     event_.Wait();
  42   }
  43
  44   void Signal() {
  45 #if DCHECK_IS_ON()
  46     DCHECK(!signaled_);
  47     signaled_ = true;
  48 #endif
  49     event_.Signal();
  50   }
  51
  52  private:
  53   base::WaitableEvent event_;
  54 #if DCHECK_IS_ON()
  55   // Used to assert that Wait() and Signal() are each called exactly once.
  56   bool waited_;
  57   bool signaled_;
  58 #endif
  59 };
  60
  61 }  // namespace cc
  62
  63 #endif  // CC_BASE_COMPLETION_EVENT_H_