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// Copyright (c) 2012 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.
// This defines helpful methods for dealing with Callbacks. Because Callbacks
// are implemented using templates, with a class per callback signature, adding
// methods to Callback<> itself is unattractive (lots of extra code gets
// generated). Instead, consider adding methods here.
//
// ResetAndReturn(&cb) is like cb.Reset() but allows executing a callback (via a
// move or copy) after the original callback is Reset(). This can be handy if
// Run() reads/writes the variable holding the Callback.
#ifndef BASE_CALLBACK_HELPERS_H_
#define BASE_CALLBACK_HELPERS_H_
#include <utility>
#include "base/atomicops.h"
#include "base/bind.h"
#include "base/callback.h"
#include "base/compiler_specific.h"
#include "base/macros.h"
#include "base/memory/ptr_util.h"
namespace base {
template <typename CallbackType>
CallbackType ResetAndReturn(CallbackType* cb) {
CallbackType ret(std::move(*cb));
DCHECK(!*cb);
return ret;
}
namespace internal {
template <typename... Args>
class AdaptCallbackForRepeatingHelper final {
public:
explicit AdaptCallbackForRepeatingHelper(OnceCallback<void(Args...)> callback)
: callback_(std::move(callback)) {
DCHECK(callback_);
}
void Run(Args... args) {
if (subtle::NoBarrier_AtomicExchange(&has_run_, 1))
return;
DCHECK(callback_);
std::move(callback_).Run(std::forward<Args>(args)...);
}
private:
volatile subtle::Atomic32 has_run_ = 0;
base::OnceCallback<void(Args...)> callback_;
DISALLOW_COPY_AND_ASSIGN(AdaptCallbackForRepeatingHelper);
};
} // namespace internal
// Wraps the given OnceCallback into a RepeatingCallback that relays its
// invocation to the original OnceCallback on the first invocation. The
// following invocations are just ignored.
template <typename... Args>
RepeatingCallback<void(Args...)> AdaptCallbackForRepeating(
OnceCallback<void(Args...)> callback) {
using Helper = internal::AdaptCallbackForRepeatingHelper<Args...>;
return base::BindRepeating(&Helper::Run,
std::make_unique<Helper>(std::move(callback)));
}
// ScopedClosureRunner is akin to std::unique_ptr<> for Closures. It ensures
// that the Closure is executed no matter how the current scope exits.
class BASE_EXPORT ScopedClosureRunner {
public:
ScopedClosureRunner();
explicit ScopedClosureRunner(OnceClosure closure);
~ScopedClosureRunner();
ScopedClosureRunner(ScopedClosureRunner&& other);
// Releases the current closure if it's set and replaces it with the closure
// from |other|.
ScopedClosureRunner& operator=(ScopedClosureRunner&& other);
// Calls the current closure and resets it, so it wont be called again.
void RunAndReset();
// Replaces closure with the new one releasing the old one without calling it.
void ReplaceClosure(OnceClosure closure);
// Releases the Closure without calling.
OnceClosure Release() WARN_UNUSED_RESULT;
private:
OnceClosure closure_;
DISALLOW_COPY_AND_ASSIGN(ScopedClosureRunner);
};
} // namespace base
#endif // BASE_CALLBACK_HELPERS_H_
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