143 lines
4.9 KiB
C++
143 lines
4.9 KiB
C++
/*
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* Copyright (c) Facebook, Inc. and its affiliates.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#pragma once
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#include <folly/Portability.h>
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#include <folly/executors/InlineExecutor.h>
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#include <folly/futures/Promise.h>
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#include <folly/lang/Exception.h>
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namespace folly {
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/*
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* SharedPromise provides the same interface as Promise, but you can extract
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* multiple Futures from it, i.e. you can call getFuture() as many times as
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* you'd like. When the SharedPromise is fulfilled, all of the Futures are
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* completed. Calls to getFuture() after the SharedPromise is fulfilled return
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* a completed Future. If you find yourself constructing collections of Promises
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* and fulfilling them simultaneously with the same value, consider this
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* utility instead. Likewise, if you find yourself in need of setting multiple
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* callbacks on the same Future (which is indefinitely unsupported), consider
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* refactoring to use SharedPromise to "split" the Future.
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*
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* The SharedPromise must be kept alive manually. Consider FutureSplitter for
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* automatic lifetime management.
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*/
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template <class T>
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class SharedPromise {
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public:
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/**
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* Return a Future tied to the shared core state. Unlike Promise::getFuture,
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* this can be called an unlimited number of times per SharedPromise.
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*/
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SemiFuture<T> getSemiFuture() const;
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/**
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* Return a Future tied to the shared core state. Unlike Promise::getFuture,
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* this can be called an unlimited number of times per SharedPromise.
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* NOTE: This function is deprecated. Please use getSemiFuture and pass the
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* appropriate executor to .via on the returned SemiFuture to get a
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* valid Future where necessary.
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*/
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Future<T> getFuture() const;
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/** Return the number of Futures associated with this SharedPromise */
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size_t size() const;
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/** Fulfill the SharedPromise with an exception_wrapper */
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void setException(exception_wrapper ew);
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/** Fulfill the SharedPromise with an exception type E, which can be passed to
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make_exception_wrapper(). Useful for originating exceptions. If you
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caught an exception the exception_wrapper form is more appropriate.
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*/
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template <class E>
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typename std::enable_if<std::is_base_of<std::exception, E>::value>::type
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setException(E const&);
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/// Set an interrupt handler to handle interrupts. See the documentation for
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/// Future::raise(). Your handler can do whatever it wants, but if you
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/// bother to set one then you probably will want to fulfill the SharedPromise
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/// with an exception (or special value) indicating how the interrupt was
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/// handled.
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void setInterruptHandler(std::function<void(exception_wrapper const&)>);
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/// Sugar to fulfill this SharedPromise<Unit>
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template <class B = T>
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typename std::enable_if<std::is_same<Unit, B>::value, void>::type setValue() {
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setTry(Try<T>(T()));
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}
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/** Set the value (use perfect forwarding for both move and copy) */
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template <class M>
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void setValue(M&& value);
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void setTry(Try<T>&& t);
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/** Fulfill this SharedPromise with the result of a function that takes no
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arguments and returns something implicitly convertible to T.
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Captures exceptions. e.g.
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p.setWith([] { do something that may throw; return a T; });
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*/
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template <class F>
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void setWith(F&& func);
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bool isFulfilled() const;
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private:
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// this allows SharedPromise move-ctor/move-assign to be defaulted
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struct Mutex : std::mutex {
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Mutex() = default;
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Mutex(Mutex&&) noexcept {}
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Mutex& operator=(Mutex&&) noexcept {
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return *this;
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}
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};
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template <typename V>
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struct Defaulted {
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using Noexcept = StrictConjunction<
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std::is_nothrow_default_constructible<V>,
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std::is_nothrow_move_constructible<V>,
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std::is_nothrow_move_assignable<V>>;
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V value{V()};
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Defaulted() = default;
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Defaulted(Defaulted&& that) noexcept(Noexcept::value)
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: value(std::exchange(that.value, V())) {}
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Defaulted& operator=(Defaulted&& that) noexcept(Noexcept::value) {
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value = std::exchange(that.value, V());
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return *this;
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}
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};
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bool hasResult() const {
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return try_.value.hasValue() || try_.value.hasException();
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}
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mutable Mutex mutex_;
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mutable Defaulted<size_t> size_;
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Defaulted<Try<T>> try_;
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mutable std::vector<Promise<T>> promises_;
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std::function<void(exception_wrapper const&)> interruptHandler_;
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};
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} // namespace folly
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#include <folly/futures/Future.h>
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#include <folly/futures/SharedPromise-inl.h>
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