Upstream Chrome on iOS source code [1/11].

ios/chrome/browser/callback_counter.h

+// Copyright 2015 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 IOS_CHROME_BROWSER_CALLBACK_COUNTER_H_
+#define IOS_CHROME_BROWSER_CALLBACK_COUNTER_H_
+
+#include "base/callback.h"
+#include "base/logging.h"
+#include "base/memory/ref_counted.h"
+#include "base/threading/thread.h"
+
+// A helper class that keeps count of the number of pending callbacks that need
+// to be received. Calls |final_callback| when all callbacks have been received.
+// All methods (except the destructor) must be called on the same thread.
+class CallbackCounter : public base::RefCounted<CallbackCounter> {
+ public:
+  typedef base::Callback<void()> FinalCallback;
+
+  explicit CallbackCounter(const FinalCallback& final_callback);
+
+  // Increments the count of pending callbacks.
+  void IncrementCount();
+  // Decrements the count of pending callbacks.
+  void DecrementCount();
+
+ private:
+  friend class base::RefCounted<CallbackCounter>;
+
+  ~CallbackCounter();
+
+  // The number of callbacks that still need to be received.
+  unsigned callback_count_;
+  // The callback that is finally called when all callbacks have been received
+  // (when the |callback_count_| goes down to 0).
+  FinalCallback final_callback_;
+  base::ThreadChecker thread_checker_;
+
+  DISALLOW_COPY_AND_ASSIGN(CallbackCounter);
+};
+
+#endif  // IOS_CHROME_BROWSER_CALLBACK_COUNTER_H_