Add a BarrierClosure.

base/barrier_closure.cc

Index: base/barrier_closure.cc
diff --git a/base/barrier_closure.cc b/base/barrier_closure.cc
new file mode 100644
index 0000000000000000000000000000000000000000..9dd914447bc7a7a55b600a5ed7ca19b9edb00380
--- /dev/null
+++ b/base/barrier_closure.cc
@@ -0,0 +1,52 @@
+// 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.
+
+#include "base/barrier_closure.h"
+
+#include "base/atomic_ref_count.h"
+#include "base/bind.h"
+
+namespace {
+
+// Maintains state for a BarrierClosure.
+class BarrierInfo {
+ public:
+  BarrierInfo(int num_callbacks_left, const base::Closure& done_closure);
+  void Run();
+
+ private:
+  base::AtomicRefCount num_callbacks_left_;
+  base::Closure done_closure_;
+};
+
+BarrierInfo::BarrierInfo(int num_callbacks, const base::Closure& done_closure)
+    : num_callbacks_left_(num_callbacks),
+      done_closure_(done_closure) {
+}
+
+void BarrierInfo::Run() {
+  DCHECK(!base::AtomicRefCountIsZero(&num_callbacks_left_));
+  if (!base::AtomicRefCountDec(&num_callbacks_left_)) {
+    done_closure_.Run();
+    done_closure_.Reset();
+  }
+}
+
+}  // namespace
+
+namespace base {
+
+base::Closure BarrierClosure(int num_callbacks_left,
+                             const base::Closure& done_closure) {
+  DCHECK(num_callbacks_left >= 0);
+
+  if (num_callbacks_left == 0)
+    done_closure.Run();
+
+  return base::Bind(&BarrierInfo::Run,
+                    base::Owned(
+                        new BarrierInfo(num_callbacks_left, done_closure)));
+}
+
+}  // namespace base