base::Bind: Implement CancelableCallback to replace CancelableTaske.

base/cancelable_callback.h

+// Copyright (c) 2011 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.
+//
+// CancelableCallback is a wrapper around base::Callback that allows
+// cancellation of a callback. CancelableCallback takes a reference on the
+// wrapped callback until this object is destroyed or Reset()/Cancel() are
+// called.
+//
+// Thread-safety notes:
+//
+// CancelableCallback objects must be created on, posted to, cancelled on, and
+// destroyed on the same thread.
+//
+//
+// EXAMPLE USAGE:
+//
+// In the following example, the test is verifying that RunIntensiveTest()
+// Quit()s the message loop within 4 seconds. The cancelable callback is posted
+// to the message loop, the intensive test runs, the message loop is run,
+// then the callback is cancelled.
+//
+// void TimeoutCallback(const std::string& timeout_message) {
+//   FAIL() << timeout_message;
+//   MessageLoop::current()->Quit();
+// }
+//
+// CancelableCallback timeout(base::Bind(TimeoutCallback));
+// MessageLoop::current()->PostDelayedTask(FROM_HERE, timeout.callback(),
+//                                         4000)  // 4 seconds to run.
+// RunIntensiveTest();
+// MessageLoop::current()->Run();
+// timeout.Cancel();  // Hopefully this is hit before the timeout callback runs.
+//
+
+#ifndef BASE_CANCELABLE_CALLBACK_H_
+#define BASE_CANCELABLE_CALLBACK_H_
+#pragma once
+
+#include "base/callback.h"
+#include "base/base_export.h"
+#include "base/memory/weak_ptr.h"
+
+namespace base {
+
+class BASE_EXPORT CancelableCallback {
+ public:
+  CancelableCallback();
+
+  // |callback| must not be null.
+  explicit CancelableCallback(const base::Closure& callback);
+
+  ~CancelableCallback();
+
+  // Cancels and drops the reference to the wrapped callback.
+  void Cancel();
+
+  // Returns true if the wrapped callback has been cancelled.
+  bool IsCancelled() const;
+
+  // Sets |callback| as the closure that may be cancelled. |callback| may not
+  // be null. Outstanding and any previously wrapped callbacks are cancelled.
+  void Reset(const base::Closure& callback);
+
+  // Returns a callback that can be disabled by calling Cancel().
+  const base::Closure& callback() const;
+
+ private:
+  void RunCallback();
+
+  // Helper method to bind |forwarder_| using a weak pointer from
+  // |weak_factory_|.
+  void InitializeForwarder();
+
+  // Used to ensure RunCallback() is not run when this object is destroyed.
+  base::WeakPtrFactory<CancelableCallback> weak_factory_;
+
+  // The wrapper closure.
+  base::Closure forwarder_;
+
+  // The stored closure that may be cancelled.
+  base::Closure callback_;
+
+  DISALLOW_COPY_AND_ASSIGN(CancelableCallback);
+};
+
+}  // namespace base
+
+#endif  // BASE_CANCELABLE_CALLBACK_H_