128 lines
4.0 KiB
C++
128 lines
4.0 KiB
C++
// Copyright (c) 2012 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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// This defines helpful methods for dealing with Callbacks. Because Callbacks
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// are implemented using templates, with a class per callback signature, adding
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// methods to Callback<> itself is unattractive (lots of extra code gets
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// generated). Instead, consider adding methods here.
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#ifndef BASE_CALLBACK_HELPERS_H_
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#define BASE_CALLBACK_HELPERS_H_
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#include <type_traits>
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#include <utility>
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#include "base/atomicops.h"
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#include "base/bind.h"
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#include "base/callback.h"
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#include "base/compiler_specific.h"
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#include "base/macros.h"
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#include "base/memory/ptr_util.h"
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namespace base {
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namespace internal {
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template <typename T>
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struct IsBaseCallbackImpl : std::false_type {};
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template <typename R, typename... Args>
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struct IsBaseCallbackImpl<OnceCallback<R(Args...)>> : std::true_type {};
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template <typename R, typename... Args>
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struct IsBaseCallbackImpl<RepeatingCallback<R(Args...)>> : std::true_type {};
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} // namespace internal
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template <typename T>
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using IsBaseCallback = internal::IsBaseCallbackImpl<std::decay_t<T>>;
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// SFINAE friendly enabler allowing to overload methods for both Repeating and
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// OnceCallbacks.
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//
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// Usage:
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// template <template <typename> class CallbackType,
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// ... other template args ...,
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// typename = EnableIfIsBaseCallback<CallbackType>>
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// void DoStuff(CallbackType<...> cb, ...);
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template <template <typename> class CallbackType>
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using EnableIfIsBaseCallback =
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std::enable_if_t<IsBaseCallback<CallbackType<void()>>::value>;
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namespace internal {
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template <typename... Args>
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class AdaptCallbackForRepeatingHelper final {
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public:
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explicit AdaptCallbackForRepeatingHelper(OnceCallback<void(Args...)> callback)
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: callback_(std::move(callback)) {
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DCHECK(callback_);
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}
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void Run(Args... args) {
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if (subtle::NoBarrier_AtomicExchange(&has_run_, 1))
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return;
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DCHECK(callback_);
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std::move(callback_).Run(std::forward<Args>(args)...);
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}
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private:
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volatile subtle::Atomic32 has_run_ = 0;
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base::OnceCallback<void(Args...)> callback_;
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DISALLOW_COPY_AND_ASSIGN(AdaptCallbackForRepeatingHelper);
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};
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} // namespace internal
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// Wraps the given OnceCallback into a RepeatingCallback that relays its
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// invocation to the original OnceCallback on the first invocation. The
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// following invocations are just ignored.
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//
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// Note that this deliberately subverts the Once/Repeating paradigm of Callbacks
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// but helps ease the migration from old-style Callbacks. Avoid if possible; use
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// if necessary for migration. TODO(tzik): Remove it. https://crbug.com/730593
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template <typename... Args>
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RepeatingCallback<void(Args...)> AdaptCallbackForRepeating(
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OnceCallback<void(Args...)> callback) {
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using Helper = internal::AdaptCallbackForRepeatingHelper<Args...>;
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return base::BindRepeating(&Helper::Run,
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std::make_unique<Helper>(std::move(callback)));
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}
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// ScopedClosureRunner is akin to std::unique_ptr<> for Closures. It ensures
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// that the Closure is executed no matter how the current scope exits.
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// If you are looking for "ScopedCallback", "CallbackRunner", or
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// "CallbackScoper" this is the class you want.
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class BASE_EXPORT ScopedClosureRunner {
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public:
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ScopedClosureRunner();
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explicit ScopedClosureRunner(OnceClosure closure);
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~ScopedClosureRunner();
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ScopedClosureRunner(ScopedClosureRunner&& other);
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// Releases the current closure if it's set and replaces it with the closure
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// from |other|.
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ScopedClosureRunner& operator=(ScopedClosureRunner&& other);
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// Calls the current closure and resets it, so it wont be called again.
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void RunAndReset();
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// Replaces closure with the new one releasing the old one without calling it.
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void ReplaceClosure(OnceClosure closure);
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// Releases the Closure without calling.
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OnceClosure Release() WARN_UNUSED_RESULT;
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private:
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OnceClosure closure_;
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DISALLOW_COPY_AND_ASSIGN(ScopedClosureRunner);
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};
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} // namespace base
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#endif // BASE_CALLBACK_HELPERS_H_
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