2 * Copyright 2016 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>
20 #include <folly/Portability.h>
25 * SharedPromise provides the same interface as Promise, but you can extract
26 * multiple Futures from it, i.e. you can call getFuture() as many times as
27 * you'd like. When the SharedPromise is fulfilled, all of the Futures will be
28 * called back. Calls to getFuture() after the SharedPromise is fulfilled return
29 * a completed Future. If you find yourself constructing collections of Promises
30 * and fulfilling them simultaneously with the same value, consider this
31 * utility instead. Likewise, if you find yourself in need of setting multiple
32 * callbacks on the same Future (which is indefinitely unsupported), consider
33 * refactoring to use SharedPromise to "split" the Future.
38 SharedPromise() = default;
39 ~SharedPromise() = default;
42 SharedPromise(SharedPromise const&) = delete;
43 SharedPromise& operator=(SharedPromise const&) = delete;
46 SharedPromise(SharedPromise<T>&&) noexcept;
47 SharedPromise& operator=(SharedPromise<T>&&) noexcept;
50 * Provide a way to split a Future<T>. Note that while the Futures from
51 * `getFuture()' depend on the completion of the parameter Future they do not
52 * inherit any other properties such as Executor's passed to `via' etc.
54 explicit SharedPromise(Future<T>);
57 * Return a Future tied to the shared core state. Unlike Promise::getFuture,
58 * this can be called an unlimited number of times per SharedPromise.
60 Future<T> getFuture();
62 /** Return the number of Futures associated with this SharedPromise */
65 /** Fulfill the SharedPromise with an exception_wrapper */
66 void setException(exception_wrapper ew);
68 /** Fulfill the SharedPromise with an exception_ptr, e.g.
72 p.setException(std::current_exception());
75 FOLLY_DEPRECATED("use setException(exception_wrapper)")
76 void setException(std::exception_ptr const&);
78 /** Fulfill the SharedPromise with an exception type E, which can be passed to
79 std::make_exception_ptr(). Useful for originating exceptions. If you
80 caught an exception the exception_wrapper form is more appropriate.
83 typename std::enable_if<std::is_base_of<std::exception, E>::value>::type
84 setException(E const&);
86 /// Set an interrupt handler to handle interrupts. See the documentation for
87 /// Future::raise(). Your handler can do whatever it wants, but if you
88 /// bother to set one then you probably will want to fulfill the SharedPromise with
89 /// an exception (or special value) indicating how the interrupt was
91 void setInterruptHandler(std::function<void(exception_wrapper const&)>);
93 /// Sugar to fulfill this SharedPromise<Unit>
94 template <class B = T>
95 typename std::enable_if<std::is_same<Unit, B>::value, void>::type
100 /** Set the value (use perfect forwarding for both move and copy) */
102 void setValue(M&& value);
104 void setTry(Try<T>&& t);
106 /** Fulfill this SharedPromise with the result of a function that takes no
107 arguments and returns something implicitly convertible to T.
108 Captures exceptions. e.g.
110 p.setWith([] { do something that may throw; return a T; });
113 void setWith(F&& func);
120 bool hasValue_{false};
122 std::vector<Promise<T>> promises_;
123 std::function<void(exception_wrapper const&)> interruptHandler_;
128 #include <folly/futures/Future.h>
129 #include <folly/futures/SharedPromise-inl.h>