Add a BarrierClosure.

base/barrier_closure.h

Index: base/barrier_closure.h
diff --git a/base/barrier_closure.h b/base/barrier_closure.h
new file mode 100644
index 0000000000000000000000000000000000000000..65cdd50567f804306fcbc3eef8f9e830d08af3d5
--- /dev/null
+++ b/base/barrier_closure.h
@@ -0,0 +1,24 @@
+// Copyright (c) 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef BASE_BARRIER_CLOSURE_

[awong, 2013/08/22 21:28:33]

BASE_BARRIER_CLOSURE_ -> BASE_BARRIER_CLOSURE_H_

[groby-ooo-7-16, 2013/08/22 21:59:45]

Done.

+#define BASE_BARRIER_CLOSURE_
+
+#include "base/base_export.h"
+#include "base/callback_forward.h"
+
+namespace base {
+
+// BarrierClosure executes |done_closure| after it has been invoked
+// |num_closures| times.
+//
+// If |num_closures| is 0, |done_closure| is executed immediately.
+//
+// BarrierClosure is thread-safe - the count of remaining closures is
+// maintained as a base::AtomicRefCount.

[awong, 2013/08/22 21:28:33]

This should note the threading assumptions about where done_closure will be run,
and when it will be released.

[groby-ooo-7-16, 2013/08/22 21:59:45]

Done.

+BASE_EXPORT base::Closure BarrierClosure(int num_closures,
+                                         const base::Closure& done_closure);
+
+}  // base

[awong, 2013/08/22 21:28:33]

}  // namesapce base

#endif  // BASE_BARRIER_CLOSURE_H_

[groby-ooo-7-16, 2013/08/22 21:59:45]

Done.

+#endif  // BASE_BARRIER_CLOSURE_