| // 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. |
| // |
| // NOTE: Header files that do not require the full definition of |
| // base::{Once,Repeating}Callback or base::{Once,Repeating}Closure should |
| // #include "base/callback_forward.h" instead of this file. |
| |
| #ifndef BASE_CALLBACK_H_ |
| #define BASE_CALLBACK_H_ |
| |
| #include <stddef.h> |
| #include <utility> |
| |
| #include "base/bind.h" |
| #include "base/callback_forward.h" |
| #include "base/callback_internal.h" |
| #include "base/check.h" |
| #include "base/notreached.h" |
| |
| // ----------------------------------------------------------------------------- |
| // Usage documentation |
| // ----------------------------------------------------------------------------- |
| // |
| // Overview: |
| // A callback is similar in concept to a function pointer: it wraps a runnable |
| // object such as a function, method, lambda, or even another callback, allowing |
| // the runnable object to be invoked later via the callback object. |
| // |
| // Unlike function pointers, callbacks are created with base::BindOnce() or |
| // base::BindRepeating() and support partial function application. |
| // |
| // A base::OnceCallback may be Run() at most once; a base::RepeatingCallback may |
| // be Run() any number of times. |is_null()| is guaranteed to return true for a |
| // moved-from callback. |
| // |
| // // The lambda takes two arguments, but the first argument |x| is bound at |
| // // callback creation. |
| // base::OnceCallback<int(int)> cb = base::BindOnce([] (int x, int y) { |
| // return x + y; |
| // }, 1); |
| // // Run() only needs the remaining unbound argument |y|. |
| // printf("1 + 2 = %d\n", std::move(cb).Run(2)); // Prints 3 |
| // printf("cb is null? %s\n", |
| // cb.is_null() ? "true" : "false"); // Prints true |
| // std::move(cb).Run(2); // Crashes since |cb| has already run. |
| // |
| // Callbacks also support cancellation. A common use is binding the receiver |
| // object as a WeakPtr<T>. If that weak pointer is invalidated, calling Run() |
| // will be a no-op. Note that |IsCancelled()| and |is_null()| are distinct: |
| // simply cancelling a callback will not also make it null. |
| // |
| // See //docs/callback.md for the full documentation. |
| |
| namespace base { |
| |
| namespace internal { |
| |
| struct NullCallbackTag { |
| template <typename Signature> |
| struct WithSignature {}; |
| }; |
| |
| struct DoNothingCallbackTag { |
| template <typename Signature> |
| struct WithSignature {}; |
| }; |
| |
| } // namespace internal |
| |
| template <typename R, typename... Args> |
| class OnceCallback<R(Args...)> : public internal::CallbackBase { |
| public: |
| using ResultType = R; |
| using RunType = R(Args...); |
| using PolymorphicInvoke = R (*)(internal::BindStateBase*, |
| internal::PassingType<Args>...); |
| |
| constexpr OnceCallback() = default; |
| OnceCallback(std::nullptr_t) = delete; |
| |
| constexpr OnceCallback(internal::NullCallbackTag) : OnceCallback() {} |
| constexpr OnceCallback& operator=(internal::NullCallbackTag) { |
| *this = OnceCallback(); |
| return *this; |
| } |
| |
| constexpr OnceCallback(internal::NullCallbackTag::WithSignature<RunType>) |
| : OnceCallback(internal::NullCallbackTag()) {} |
| constexpr OnceCallback& operator=( |
| internal::NullCallbackTag::WithSignature<RunType>) { |
| *this = internal::NullCallbackTag(); |
| return *this; |
| } |
| |
| constexpr OnceCallback(internal::DoNothingCallbackTag) |
| : OnceCallback(BindOnce([](Args... args) {})) {} |
| constexpr OnceCallback& operator=(internal::DoNothingCallbackTag) { |
| *this = BindOnce([](Args... args) {}); |
| return *this; |
| } |
| |
| constexpr OnceCallback(internal::DoNothingCallbackTag::WithSignature<RunType>) |
| : OnceCallback(internal::DoNothingCallbackTag()) {} |
| constexpr OnceCallback& operator=( |
| internal::DoNothingCallbackTag::WithSignature<RunType>) { |
| *this = internal::DoNothingCallbackTag(); |
| return *this; |
| } |
| |
| explicit OnceCallback(internal::BindStateBase* bind_state) |
| : internal::CallbackBase(bind_state) {} |
| |
| OnceCallback(const OnceCallback&) = delete; |
| OnceCallback& operator=(const OnceCallback&) = delete; |
| |
| OnceCallback(OnceCallback&&) noexcept = default; |
| OnceCallback& operator=(OnceCallback&&) noexcept = default; |
| |
| OnceCallback(RepeatingCallback<RunType> other) |
| : internal::CallbackBase(std::move(other)) {} |
| |
| OnceCallback& operator=(RepeatingCallback<RunType> other) { |
| static_cast<internal::CallbackBase&>(*this) = std::move(other); |
| return *this; |
| } |
| |
| R Run(Args... args) const & { |
| static_assert(!sizeof(*this), |
| "OnceCallback::Run() may only be invoked on a non-const " |
| "rvalue, i.e. std::move(callback).Run()."); |
| NOTREACHED(); |
| } |
| |
| R Run(Args... args) && { |
| // Move the callback instance into a local variable before the invocation, |
| // that ensures the internal state is cleared after the invocation. |
| // It's not safe to touch |this| after the invocation, since running the |
| // bound function may destroy |this|. |
| OnceCallback cb = std::move(*this); |
| PolymorphicInvoke f = |
| reinterpret_cast<PolymorphicInvoke>(cb.polymorphic_invoke()); |
| return f(cb.bind_state_.get(), std::forward<Args>(args)...); |
| } |
| |
| // Then() returns a new OnceCallback that receives the same arguments as |
| // |this|, and with the return type of |then|. The returned callback will: |
| // 1) Run the functor currently bound to |this| callback. |
| // 2) Run the |then| callback with the result from step 1 as its single |
| // argument. |
| // 3) Return the value from running the |then| callback. |
| // |
| // Since this method generates a callback that is a replacement for `this`, |
| // `this` will be consumed and reset to a null callback to ensure the |
| // originally-bound functor can be run at most once. |
| template <typename ThenR, typename... ThenArgs> |
| OnceCallback<ThenR(Args...)> Then(OnceCallback<ThenR(ThenArgs...)> then) && { |
| CHECK(then); |
| return BindOnce( |
| internal::ThenHelper< |
| OnceCallback, OnceCallback<ThenR(ThenArgs...)>>::CreateTrampoline(), |
| std::move(*this), std::move(then)); |
| } |
| |
| // This overload is required; even though RepeatingCallback is implicitly |
| // convertible to OnceCallback, that conversion will not used when matching |
| // for template argument deduction. |
| template <typename ThenR, typename... ThenArgs> |
| OnceCallback<ThenR(Args...)> Then( |
| RepeatingCallback<ThenR(ThenArgs...)> then) && { |
| CHECK(then); |
| return BindOnce( |
| internal::ThenHelper< |
| OnceCallback, |
| RepeatingCallback<ThenR(ThenArgs...)>>::CreateTrampoline(), |
| std::move(*this), std::move(then)); |
| } |
| }; |
| |
| template <typename R, typename... Args> |
| class RepeatingCallback<R(Args...)> : public internal::CallbackBaseCopyable { |
| public: |
| using ResultType = R; |
| using RunType = R(Args...); |
| using PolymorphicInvoke = R (*)(internal::BindStateBase*, |
| internal::PassingType<Args>...); |
| |
| constexpr RepeatingCallback() = default; |
| RepeatingCallback(std::nullptr_t) = delete; |
| |
| constexpr RepeatingCallback(internal::NullCallbackTag) |
| : RepeatingCallback() {} |
| constexpr RepeatingCallback& operator=(internal::NullCallbackTag) { |
| *this = RepeatingCallback(); |
| return *this; |
| } |
| |
| constexpr RepeatingCallback(internal::NullCallbackTag::WithSignature<RunType>) |
| : RepeatingCallback(internal::NullCallbackTag()) {} |
| constexpr RepeatingCallback& operator=( |
| internal::NullCallbackTag::WithSignature<RunType>) { |
| *this = internal::NullCallbackTag(); |
| return *this; |
| } |
| |
| constexpr RepeatingCallback(internal::DoNothingCallbackTag) |
| : RepeatingCallback(BindRepeating([](Args... args) {})) {} |
| constexpr RepeatingCallback& operator=(internal::DoNothingCallbackTag) { |
| *this = BindRepeating([](Args... args) {}); |
| return *this; |
| } |
| |
| constexpr RepeatingCallback( |
| internal::DoNothingCallbackTag::WithSignature<RunType>) |
| : RepeatingCallback(internal::DoNothingCallbackTag()) {} |
| constexpr RepeatingCallback& operator=( |
| internal::DoNothingCallbackTag::WithSignature<RunType>) { |
| *this = internal::DoNothingCallbackTag(); |
| return *this; |
| } |
| |
| explicit RepeatingCallback(internal::BindStateBase* bind_state) |
| : internal::CallbackBaseCopyable(bind_state) {} |
| |
| // Copyable and movable. |
| RepeatingCallback(const RepeatingCallback&) = default; |
| RepeatingCallback& operator=(const RepeatingCallback&) = default; |
| RepeatingCallback(RepeatingCallback&&) noexcept = default; |
| RepeatingCallback& operator=(RepeatingCallback&&) noexcept = default; |
| |
| bool operator==(const RepeatingCallback& other) const { |
| return EqualsInternal(other); |
| } |
| |
| bool operator!=(const RepeatingCallback& other) const { |
| return !operator==(other); |
| } |
| |
| R Run(Args... args) const & { |
| PolymorphicInvoke f = |
| reinterpret_cast<PolymorphicInvoke>(this->polymorphic_invoke()); |
| return f(this->bind_state_.get(), std::forward<Args>(args)...); |
| } |
| |
| R Run(Args... args) && { |
| // Move the callback instance into a local variable before the invocation, |
| // that ensures the internal state is cleared after the invocation. |
| // It's not safe to touch |this| after the invocation, since running the |
| // bound function may destroy |this|. |
| RepeatingCallback cb = std::move(*this); |
| PolymorphicInvoke f = |
| reinterpret_cast<PolymorphicInvoke>(cb.polymorphic_invoke()); |
| return f(std::move(cb).bind_state_.get(), std::forward<Args>(args)...); |
| } |
| |
| // Then() returns a new RepeatingCallback that receives the same arguments as |
| // |this|, and with the return type of |then|. The |
| // returned callback will: |
| // 1) Run the functor currently bound to |this| callback. |
| // 2) Run the |then| callback with the result from step 1 as its single |
| // argument. |
| // 3) Return the value from running the |then| callback. |
| // |
| // If called on an rvalue (e.g. std::move(cb).Then(...)), this method |
| // generates a callback that is a replacement for `this`. Therefore, `this` |
| // will be consumed and reset to a null callback to ensure the |
| // originally-bound functor will be run at most once. |
| template <typename ThenR, typename... ThenArgs> |
| RepeatingCallback<ThenR(Args...)> Then( |
| RepeatingCallback<ThenR(ThenArgs...)> then) const& { |
| CHECK(then); |
| return BindRepeating( |
| internal::ThenHelper< |
| RepeatingCallback, |
| RepeatingCallback<ThenR(ThenArgs...)>>::CreateTrampoline(), |
| *this, std::move(then)); |
| } |
| |
| template <typename ThenR, typename... ThenArgs> |
| RepeatingCallback<ThenR(Args...)> Then( |
| RepeatingCallback<ThenR(ThenArgs...)> then) && { |
| CHECK(then); |
| return BindRepeating( |
| internal::ThenHelper< |
| RepeatingCallback, |
| RepeatingCallback<ThenR(ThenArgs...)>>::CreateTrampoline(), |
| std::move(*this), std::move(then)); |
| } |
| }; |
| |
| } // namespace base |
| |
| #endif // BASE_CALLBACK_H_ |