Implement condition variables on Windows on top of Event/SetEvent/ResetEvent.

runtime/platform/thread_win.h

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef PLATFORM_THREAD_WIN_H_
 #define PLATFORM_THREAD_WIN_H_
 
 #if !defined(PLATFORM_THREAD_H_)
 #error Do not include thread_win.h directly; use thread.h instead.
 #endif
@@ skipping 36 matching lines @@
   DISALLOW_COPY_AND_ASSIGN(MutexData);
 };
 
 
 class MonitorData {
  private:
   MonitorData() {}
   ~MonitorData() {}
 
   CRITICAL_SECTION cs_;
-  // TODO(ager): Condition variables only available since Windows
-  // Vista. Therefore, this is only a temporary solution. We will have
-  // to implement simple condition variables for use in Windows XP and
-  // earlier.
-  CONDITION_VARIABLE cond_;
+
+  // Condition variables are only available since Windows Vista. To
+  // support at least Windows XP, we implement our own condition
+  // variables using SetEvent on Event objects.
+
+  // The notify_event_ is an auto-reset event which means that
+  // SetEvent only wakes up one waiter.
+  HANDLE notify_event_;
+
+  // The notify_all_event_ is a manual-reset event which means that
+  // SetEvent wakes up all waiters.
+  HANDLE notify_all_event_;
+
+  // Counter with protection used to determine the right time to reset
+  // the notify_all_event_.
+  CRITICAL_SECTION waiters_cs_;
+  intptr_t waiters_;
 
   friend class Monitor;
 
   DISALLOW_ALLOCATION();
   DISALLOW_COPY_AND_ASSIGN(MonitorData);
 };
 
 }  // namespace dart
 
 #endif  // PLATFORM_THREAD_WIN_H_