cc/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_COMPLETION_EVENT_H_
   6 #define CC_COMPLETION_EVENT_H_
   7
   8 #include "base/synchronization/waitable_event.h"
   9 #include "base/threading/thread_restrictions.h"
  10 #include "base/logging.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         : m_event(false /* manual_reset */, false /* initially_signaled */)
  22     {
  23 #ifndef NDEBUG
  24         m_waited = false;
  25         m_signaled = false;
  26 #endif
  27     }
  28
  29     ~CompletionEvent()
  30     {
  31 #ifndef NDEBUG
  32         DCHECK(m_waited);
  33         DCHECK(m_signaled);
  34 #endif
  35     }
  36
  37     void wait()
  38     {
  39 #ifndef NDEBUG
  40         DCHECK(!m_waited);
  41         m_waited = true;
  42 #endif
  43         base::ThreadRestrictions::ScopedAllowWait allow_wait;
  44         m_event.Wait();
  45     }
  46
  47     void signal()
  48     {
  49 #ifndef NDEBUG
  50         DCHECK(!m_signaled);
  51         m_signaled = true;
  52 #endif
  53         m_event.Signal();
  54     }
  55
  56 private:
  57     base::WaitableEvent m_event;
  58 #ifndef NDEBUG
  59     // Used to assert that wait() and signal() are each called exactly once.
  60     bool m_waited;
  61     bool m_signaled;
  62 #endif
  63 };
  64
  65 }
  66
  67 #endif  // CC_COMPLETION_EVENT_H_