A basic wrapper for a windows event object that encapsulates the way we often use windows events. This API is not meant to be compatible with ObjectWatcher or MessageLoop::WatchObject. This API is meant to be easily ported to Mac & Linux using a traditional mutex and condition variable pairing.

There's nothing to test here since the implementation is such a thin wrapper around Win32 APIs.  However, once we go off to implement a posix version, we'll need some tests.

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@620 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 94 insertions, 0 deletions

diff --git a/base/waitable_event.h b/base/waitable_event.h
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+// Copyright 2008, Google Inc.
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//    * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//    * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//    * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#ifndef BASE_WAITABLE_EVENT_H_
+#define BASE_WAITABLE_EVENT_H_
+
+#include "base/time.h"
+
+#if defined(OS_WIN)
+typedef void* HANDLE;
+#endif
+
+namespace base {
+
+// A WaitableEvent can be a useful thread synchronization tool when you want to
+// allow one thread to wait for another thread to finish some work.
+//
+// Use a WaitableEvent when you would otherwise use a Lock+ConditionVariable to
+// protect a simple boolean value.  However, if you find yourself using a
+// WaitableEvent in conjunction with a Lock to wait for a more complex state
+// change (e.g., for an item to be added to a queue), then you should probably
+// be using a ConditionVariable instead of a WaitableEvent.
+//
+// NOTE: On Windows, this class provides a subset of the functionality afforded
+// by a Windows event object.  This is intentional.  If you are writing Windows
+// specific code and you need other features of a Windows event, then you might
+// be better off just using an Windows event directly.
+//
+class WaitableEvent {
+ public:
+  // If manual_reset is true, then to set the event state to non-signaled, a
+  // consumer must call the Reset method.  If this parameter is false, then the
+  // system automatically resets the event state to non-signaled after a single
+  // waiting thread has been released.
+  WaitableEvent(bool manual_reset, bool initially_signaled);
+
+  // WARNING: Destroying a WaitableEvent while threads are waiting on it is not
+  // supported.  Doing so will cause crashes or other instability.
+  ~WaitableEvent();
+
+  // Put the event in the un-signaled state.
+  void Reset();
+
+  // Put the event in the signaled state.  Causing any thread blocked on Wait
+  // to be woken up.
+  void Signal();
+
+  // Returns true if the event is in the signaled state, else false.
+  bool IsSignaled();
+
+  // Wait indefinitely for the event to be signaled.  Returns true if the event
+  // was signaled, else false is returned to indicate that waiting failed.
+  bool Wait();
+
+  // Wait up until max_time has passed for the event to be signaled.  Returns
+  // true if the event was signaled.  If this method returns false, then it
+  // does not necessarily mean that max_time was exceeded.
+  bool TimedWait(const TimeDelta& max_time);
+
+ private:
+#if defined(OS_WIN)
+  HANDLE event_;
+#endif
+};
+
+}  // namespace base
+
+#endif  // BASE_WAITABLE_EVENT_H_