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* Copyright 2015 Facebook, Inc.
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* See the License for the specific language governing permissions and
* limitations under the License.
#pragma once
#include <folly/futures/Promise.h>
#include <folly/Portability.h>
namespace folly {
* SharedPromise provides the same interface as Promise, but you can extract
* multiple Futures from it, i.e. you can call getFuture() as many times as
* you'd like. When the SharedPromise is fulfilled, all of the Futures will be
* called back. Calls to getFuture() after the SharedPromise is fulfilled return
* a completed Future. If you find yourself constructing collections of Promises
* and fulfilling them simultaneously with the same value, consider this
* utility instead. Likewise, if you find yourself in need of setting multiple
* callbacks on the same Future (which is indefinitely unsupported), consider
* refactoring to use SharedPromise to "split" the Future.
template <class T>
class SharedPromise {
SharedPromise() = default;
~SharedPromise() = default;
// not copyable
SharedPromise(SharedPromise const&) = delete;
SharedPromise& operator=(SharedPromise const&) = delete;
// movable
SharedPromise(SharedPromise<T>&&) noexcept;
SharedPromise& operator=(SharedPromise<T>&&) noexcept;
* Return a Future tied to the shared core state. Unlike Promise::getFuture,
* this can be called an unlimited number of times per SharedPromise.
Future<T> getFuture();
/** Return the number of Futures associated with this SharedPromise */
size_t size();
/** Fulfill the SharedPromise with an exception_wrapper */
void setException(exception_wrapper ew);
/** Fulfill the SharedPromise with an exception_ptr, e.g.
try {
} catch (...) {
FOLLY_DEPRECATED("use setException(exception_wrapper)")
void setException(std::exception_ptr const&);
/** Fulfill the SharedPromise with an exception type E, which can be passed to
std::make_exception_ptr(). Useful for originating exceptions. If you
caught an exception the exception_wrapper form is more appropriate.
template <class E>
typename std::enable_if<std::is_base_of<std::exception, E>::value>::type
setException(E const&);
/// Set an interrupt handler to handle interrupts. See the documentation for
/// Future::raise(). Your handler can do whatever it wants, but if you
/// bother to set one then you probably will want to fulfill the SharedPromise with
/// an exception (or special value) indicating how the interrupt was
/// handled.
void setInterruptHandler(std::function<void(exception_wrapper const&)>);
/// Sugar to fulfill this SharedPromise<Unit>
template <class B = T>
typename std::enable_if<std::is_same<Unit, B>::value, void>::type
setValue() {
/** Set the value (use perfect forwarding for both move and copy) */
template <class M>
void setValue(M&& value);
void setTry(Try<T>&& t);
/** Fulfill this SharedPromise with the result of a function that takes no
arguments and returns something implicitly convertible to T.
Captures exceptions. e.g.
p.setWith([] { do something that may throw; return a T; });
template <class F>
void setWith(F&& func);
std::mutex mutex_;
size_t size_{0};
bool hasValue_{false};
Try<T> try_;
std::vector<Promise<T>> promises_;
#include <folly/futures/Future.h>
#include <folly/futures/SharedPromise-inl.h>