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.
+
+#ifndef BASE_CANCELABLE_CALLBACK_H_
+#define BASE_CANCELABLE_CALLBACK_H_
+#pragma once
+

[csilv, 2011/11/23 19:37:30]

Consider adding some overview documentation here about what this class is for,
with an example snippit, similar to what is currently in callback.h.

+#include "base/bind.h"
+#include "base/bind_helpers.h"
+#include "base/callback.h"
+#include "base/compiler_specific.h"
+#include "base/memory/singleton.h"

[csilv, 2011/11/23 19:37:30]

i dont think bind.h, bind_helpers.h, compiler_specific.h, and singleton.h are
used in this header.

[James Hawkins, 2011/11/23 22:12:52]

Done.

+#include "base/memory/weak_ptr.h"
+
+namespace base {
+
+// Wrapper used to cancel a callback.
+class CancelableCallback {

[csilv, 2011/11/23 19:37:30]

i think you may need to add BASE_EXPORT (along with include for
base/base_export.h)

[James Hawkins, 2011/11/23 22:12:52]

Done.

+ public:
+  CancelableCallback();
+
+  // |callback| must not be null.

[csilv, 2011/11/23 19:37:30]

Would it be better to say "must not be a null callback"?  Not a big deal, just a
thought.

[James Hawkins, 2011/11/23 22:12:52]

"|callback| must not be a null callback" sounds weird, and there's precedence
for using "must not be null" (note the lower-case null.)

+  explicit CancelableCallback(const base::Closure& callback);
+
+  ~CancelableCallback();
+
+  // Cancels the stored callback.
+  void Cancel();
+
+  // Sets |callback| as the closure that may be cancelled. |callback| may not
+  // be null.

[awong, 2011/11/23 19:58:23]

Should state what happens to outstanding callbacks, and to any previously
wrapped callbacks.

[James Hawkins, 2011/11/23 22:12:52]

Done.

+  void Reset(const base::Closure& callback);
+
+  // Returns the wrapped callback.

[awong, 2011/11/23 19:58:23]

Returns a callback that can disabled by calling Cancel().

[James Hawkins, 2011/11/23 22:12:52]

Done.

+  const base::Closure& callback() const;
+
+  // Returns true if the wrapped callback is null.
+  bool is_null() const;
+
+ private:
+  // Closure that runs the stored callback.
+  void RunCallback();
+
+  // Helper method to bind |forwarder_| using a weak pointer from
+  // |weak_factory_|.
+  void BindForwarder();
+
+  // 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_