2 * Copyright 2015 Facebook, Inc.
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
8 * http://www.apache.org/licenses/LICENSE-2.0
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
19 #include <folly/futures/Promise.h>
24 * SharedPromise provides the same interface as Promise, but you can extract
25 * multiple Futures from it, i.e. you can call getFuture() as many times as
26 * you'd like. When the SharedPromise is fulfilled, all of the Futures will be
27 * called back. Calls to getFuture() after the SharedPromise is fulfilled return
28 * a completed Future. If you find yourself constructing collections of Promises
29 * and fulfilling them simultaneously with the same value, consider this
30 * utility instead. Likewise, if you find yourself in need of setting multiple
31 * callbacks on the same Future (which is indefinitely unsupported), consider
32 * refactoring to use SharedPromise to "split" the Future.
37 SharedPromise() = default;
38 ~SharedPromise() = default;
41 SharedPromise(SharedPromise const&) = delete;
42 SharedPromise& operator=(SharedPromise const&) = delete;
45 SharedPromise(SharedPromise<T>&&) noexcept;
46 SharedPromise& operator=(SharedPromise<T>&&) noexcept;
49 * Return a Future tied to the shared core state. Unlike Promise::getFuture,
50 * this can be called an unlimited number of times per SharedPromise.
52 Future<T> getFuture();
54 /** Return the number of Futures associated with this SharedPromise */
57 /** Fulfill the SharedPromise with an exception_wrapper */
58 void setException(exception_wrapper ew);
60 /** Fulfill the SharedPromise with an exception_ptr, e.g.
64 p.setException(std::current_exception());
67 DEPRECATED void setException(std::exception_ptr const&);
69 /** Fulfill the SharedPromise with an exception type E, which can be passed to
70 std::make_exception_ptr(). Useful for originating exceptions. If you
71 caught an exception the exception_wrapper form is more appropriate.
74 typename std::enable_if<std::is_base_of<std::exception, E>::value>::type
75 setException(E const&);
77 /// Set an interrupt handler to handle interrupts. See the documentation for
78 /// Future::raise(). Your handler can do whatever it wants, but if you
79 /// bother to set one then you probably will want to fulfill the SharedPromise with
80 /// an exception (or special value) indicating how the interrupt was
82 void setInterruptHandler(std::function<void(exception_wrapper const&)>);
84 /// Sugar to fulfill this SharedPromise<Unit>
85 template <class B = T>
86 typename std::enable_if<std::is_same<Unit, B>::value, void>::type
91 /** Set the value (use perfect forwarding for both move and copy) */
93 void setValue(M&& value);
95 void setTry(Try<T>&& t);
97 /** Fulfill this SharedPromise with the result of a function that takes no
98 arguments and returns something implicitly convertible to T.
99 Captures exceptions. e.g.
101 p.setWith([] { do something that may throw; return a T; });
104 void setWith(F&& func);
109 bool hasValue_{false};
111 std::vector<Promise<T>> promises_;
116 #include <folly/futures/Future.h>
117 #include <folly/futures/SharedPromise-inl.h>