101 lines
3.0 KiB
C
101 lines
3.0 KiB
C
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/*
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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/futures/Future.h>
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#include <folly/futures/SharedPromise.h>
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#include <folly/lang/Exception.h>
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namespace folly {
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class FOLLY_EXPORT FutureSplitterInvalid : public FutureException {
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public:
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FutureSplitterInvalid()
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: FutureException("No Future in this FutureSplitter") {}
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};
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/*
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* FutureSplitter provides a `getFuture()' method which can be called multiple
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* times, returning a new Future each time. These futures are completed when the
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* original Future passed to the FutureSplitter constructor is completed, and
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* are completed on the same executor (if any) and at the same priority as the
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* original Future. Calls to `getFuture()' after that time return a completed
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* Future.
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*/
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template <class T>
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class FutureSplitter {
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public:
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/**
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* Default constructor for convenience only. It is an error to call
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* `getFuture()` on a default-constructed FutureSplitter which has not had
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* a correctly-constructed FutureSplitter copy- or move-assigned into it.
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*/
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FutureSplitter() = default;
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/**
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* Provide a way to split a Future<T>.
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*/
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explicit FutureSplitter(Future<T>&& future)
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: promise_(std::make_shared<SharedPromise<T>>()),
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e_(getExecutorFrom(future)) {
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std::move(future).thenTry([promise = promise_](Try<T>&& theTry) {
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promise->setTry(std::move(theTry));
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});
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}
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/**
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* This can be called an unlimited number of times per FutureSplitter.
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*/
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Future<T> getFuture() {
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if (promise_ == nullptr) {
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throw_exception<FutureSplitterInvalid>();
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}
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return promise_->getSemiFuture().via(e_);
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}
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/**
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* This can be called an unlimited number of times per FutureSplitter.
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*/
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SemiFuture<T> getSemiFuture() {
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if (promise_ == nullptr) {
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throw_exception<FutureSplitterInvalid>();
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}
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return promise_->getSemiFuture();
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}
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private:
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std::shared_ptr<SharedPromise<T>> promise_;
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Executor::KeepAlive<> e_;
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static Executor* getExecutorFrom(Future<T>& f) {
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// If the passed future had a null executor, use an inline executor
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// to ensure that .via is safe
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auto* e = f.getExecutor();
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return e ? e : &InlineExecutor::instance();
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}
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};
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/**
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* Convenience function, allowing us to exploit template argument deduction to
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* improve readability.
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*/
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template <class T>
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FutureSplitter<T> splitFuture(Future<T>&& future) {
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return FutureSplitter<T>{std::move(future)};
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}
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} // namespace folly
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