mirror of
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137 lines
4.0 KiB
C++
137 lines
4.0 KiB
C++
// Copyright (c) 2011 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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//
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// CancelableCallback is a wrapper around base::Callback that allows
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// cancellation of a callback. CancelableCallback takes a reference on the
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// wrapped callback until this object is destroyed or Reset()/Cancel() are
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// called.
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//
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// NOTE:
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//
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// Calling CancelableCallback::Cancel() brings the object back to its natural,
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// default-constructed state, i.e., CancelableCallback::callback() will return
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// a null callback.
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//
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// THREAD-SAFETY:
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//
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// CancelableCallback objects must be created on, posted to, cancelled on, and
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// destroyed on the same thread.
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//
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//
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// EXAMPLE USAGE:
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//
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// In the following example, the test is verifying that RunIntensiveTest()
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// Quit()s the message loop within 4 seconds. The cancelable callback is posted
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// to the message loop, the intensive test runs, the message loop is run,
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// then the callback is cancelled.
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//
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// RunLoop run_loop;
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//
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// void TimeoutCallback(const std::string& timeout_message) {
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// FAIL() << timeout_message;
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// run_loop.QuitWhenIdle();
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// }
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//
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// CancelableClosure timeout(base::Bind(&TimeoutCallback, "Test timed out."));
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// ThreadTaskRunnerHandle::Get()->PostDelayedTask(FROM_HERE, timeout.callback(),
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// TimeDelta::FromSeconds(4));
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// RunIntensiveTest();
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// run_loop.Run();
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// timeout.Cancel(); // Hopefully this is hit before the timeout callback runs.
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//
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#ifndef BASE_CANCELABLE_CALLBACK_H_
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#define BASE_CANCELABLE_CALLBACK_H_
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#include <utility>
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#include "base/base_export.h"
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#include "base/bind.h"
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#include "base/callback.h"
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#include "base/callback_internal.h"
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#include "base/compiler_specific.h"
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#include "base/logging.h"
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#include "base/macros.h"
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#include "base/memory/weak_ptr.h"
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namespace base {
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template <typename Sig>
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class CancelableCallback;
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template <typename... A>
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class CancelableCallback<void(A...)> {
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public:
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CancelableCallback() : weak_factory_(this) {}
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// |callback| must not be null.
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explicit CancelableCallback(const base::Callback<void(A...)>& callback)
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: callback_(callback), weak_factory_(this) {
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DCHECK(!callback.is_null());
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InitializeForwarder();
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}
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~CancelableCallback() {}
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// Cancels and drops the reference to the wrapped callback.
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void Cancel() {
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weak_factory_.InvalidateWeakPtrs();
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forwarder_.Reset();
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callback_.Reset();
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}
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// Returns true if the wrapped callback has been cancelled.
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bool IsCancelled() const {
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return callback_.is_null();
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}
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// Sets |callback| as the closure that may be cancelled. |callback| may not
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// be null. Outstanding and any previously wrapped callbacks are cancelled.
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void Reset(const base::Callback<void(A...)>& callback) {
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DCHECK(!callback.is_null());
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// Outstanding tasks (e.g., posted to a message loop) must not be called.
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Cancel();
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// |forwarder_| is no longer valid after Cancel(), so re-bind.
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InitializeForwarder();
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callback_ = callback;
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}
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// Returns a callback that can be disabled by calling Cancel().
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const base::Callback<void(A...)>& callback() const {
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return forwarder_;
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}
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private:
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void Forward(A... args) const {
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callback_.Run(std::forward<A>(args)...);
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}
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// Helper method to bind |forwarder_| using a weak pointer from
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// |weak_factory_|.
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void InitializeForwarder() {
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forwarder_ = base::Bind(&CancelableCallback<void(A...)>::Forward,
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weak_factory_.GetWeakPtr());
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}
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// The wrapper closure.
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base::Callback<void(A...)> forwarder_;
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// The stored closure that may be cancelled.
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base::Callback<void(A...)> callback_;
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// Used to ensure Forward() is not run when this object is destroyed.
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base::WeakPtrFactory<CancelableCallback<void(A...)>> weak_factory_;
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DISALLOW_COPY_AND_ASSIGN(CancelableCallback);
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};
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typedef CancelableCallback<void(void)> CancelableClosure;
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} // namespace base
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#endif // BASE_CANCELABLE_CALLBACK_H_
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