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.
18 #include <folly/futures/Future.h>
22 /// This namespace is for utility functions that would usually be static
23 /// members of Future, except they don't make sense there because they don't
24 /// depend on the template type (rather, on the type of their arguments in
25 /// some cases). This is the least-bad naming scheme we could think of. Some
26 /// of the functions herein have really-likely-to-collide names, like "map"
29 /// Returns a Future that will complete after the specified duration. The
30 /// Duration typedef of a `std::chrono` duration type indicates the
31 /// resolution you can expect to be meaningful (milliseconds at the time of
32 /// writing). Normally you wouldn't need to specify a Timekeeper, we will
33 /// use the global futures timekeeper (we run a thread whose job it is to
34 /// keep time for futures timeouts) but we provide the option for power
37 /// The Timekeeper thread will be lazily created the first time it is
38 /// needed. If your program never uses any timeouts or other time-based
39 /// Futures you will pay no Timekeeper thread overhead.
40 Future<void> sleep(Duration, Timekeeper* = nullptr);
43 * Set func as the callback for each input Future and return a vector of
44 * Futures containing the results in the input order.
46 template <class It, class F,
47 class ItT = typename std::iterator_traits<It>::value_type,
49 = typename decltype(std::declval<ItT>().then(std::declval<F>()))::value_type>
50 std::vector<Future<Result>> map(It first, It last, F func);
52 // Sugar for the most common case
53 template <class Collection, class F>
54 auto map(Collection&& c, F&& func)
55 -> decltype(map(c.begin(), c.end(), func)) {
56 return map(c.begin(), c.end(), std::forward<F>(func));
62 Make a completed Future by moving in a value. e.g.
65 auto f = makeFuture(std::move(foo));
69 auto f = makeFuture<string>("foo");
72 Future<typename std::decay<T>::type> makeFuture(T&& t);
74 /** Make a completed void Future. */
75 Future<void> makeFuture();
77 /** Make a completed Future by executing a function. If the function throws
78 we capture the exception, otherwise we capture the result. */
82 typename std::enable_if<
83 !std::is_reference<F>::value, bool>::type sdf = false)
84 -> Future<decltype(func())>;
89 -> Future<decltype(func())>;
91 /// Make a failed Future from an exception_ptr.
92 /// Because the Future's type cannot be inferred you have to specify it, e.g.
94 /// auto f = makeFuture<string>(std::current_exception());
96 Future<T> makeFuture(std::exception_ptr const& e) DEPRECATED;
98 /// Make a failed Future from an exception_wrapper.
100 Future<T> makeFuture(exception_wrapper ew);
102 /** Make a Future from an exception type E that can be passed to
103 std::make_exception_ptr(). */
104 template <class T, class E>
105 typename std::enable_if<std::is_base_of<std::exception, E>::value,
107 makeFuture(E const& e);
109 /** Make a Future out of a Try */
111 Future<T> makeFuture(Try<T>&& t);
114 * Return a new Future that will call back on the given Executor.
115 * This is just syntactic sugar for makeFuture().via(executor)
117 * @param executor the Executor to call back on
118 * @param priority optionally, the priority to add with. Defaults to 0 which
119 * represents medium priority.
121 * @returns a void Future that will call back on the given executor
123 inline Future<void> via(
125 int8_t priority = Executor::MID_PRI);
127 /** When all the input Futures complete, the returned Future will complete.
128 Errors do not cause early termination; this Future will always succeed
129 after all its Futures have finished (whether successfully or with an
132 The Futures are moved in, so your copies are invalid. If you need to
133 chain further from these Futures, use the variant with an output iterator.
135 This function is thread-safe for Futures running on different threads. But
136 if you are doing anything non-trivial after, you will probably want to
137 follow with `via(executor)` because it will complete in whichever thread the
138 last Future completes in.
140 The return type for Future<T> input is a Future<std::vector<Try<T>>>
142 template <class InputIterator>
143 Future<std::vector<Try<
144 typename std::iterator_traits<InputIterator>::value_type::value_type>>>
145 collectAll(InputIterator first, InputIterator last);
147 /// Sugar for the most common case
148 template <class Collection>
149 auto collectAll(Collection&& c) -> decltype(collectAll(c.begin(), c.end())) {
150 return collectAll(c.begin(), c.end());
153 /// This version takes a varying number of Futures instead of an iterator.
154 /// The return type for (Future<T1>, Future<T2>, ...) input
155 /// is a Future<std::tuple<Try<T1>, Try<T2>, ...>>.
156 /// The Futures are moved in, so your copies are invalid.
157 template <typename... Fs>
158 typename detail::VariadicContext<
159 typename std::decay<Fs>::type::value_type...>::type
160 collectAll(Fs&&... fs);
162 /// Like collectAll, but will short circuit on the first exception. Thus, the
163 /// type of the returned Future is std::vector<T> instead of
164 /// std::vector<Try<T>>
165 template <class InputIterator>
166 Future<typename detail::CollectContext<
167 typename std::iterator_traits<InputIterator>::value_type::value_type
169 collect(InputIterator first, InputIterator last);
171 /// Sugar for the most common case
172 template <class Collection>
173 auto collect(Collection&& c) -> decltype(collect(c.begin(), c.end())) {
174 return collect(c.begin(), c.end());
177 /** The result is a pair of the index of the first Future to complete and
178 the Try. If multiple Futures complete at the same time (or are already
179 complete when passed in), the "winner" is chosen non-deterministically.
181 This function is thread-safe for Futures running on different threads.
183 template <class InputIterator>
186 Try<typename std::iterator_traits<InputIterator>::value_type::value_type>>>
187 collectAny(InputIterator first, InputIterator last);
189 /// Sugar for the most common case
190 template <class Collection>
191 auto collectAny(Collection&& c) -> decltype(collectAny(c.begin(), c.end())) {
192 return collectAny(c.begin(), c.end());
195 /** when n Futures have completed, the Future completes with a vector of
196 the index and Try of those n Futures (the indices refer to the original
197 order, but the result vector will be in an arbitrary order)
201 template <class InputIterator>
202 Future<std::vector<std::pair<
204 Try<typename std::iterator_traits<InputIterator>::value_type::value_type>>>>
205 collectN(InputIterator first, InputIterator last, size_t n);
207 /// Sugar for the most common case
208 template <class Collection>
209 auto collectN(Collection&& c, size_t n)
210 -> decltype(collectN(c.begin(), c.end(), n)) {
211 return collectN(c.begin(), c.end(), n);
214 /** window creates up to n Futures using the values
215 in the collection, and then another Future for each Future
218 this is basically a sliding window of Futures of size n
220 func must return a Future for each value in input
222 template <class Collection, class F,
223 class ItT = typename std::iterator_traits<
224 typename Collection::iterator>::value_type,
225 class Result = typename detail::resultOf<F, ItT&&>::value_type>
226 std::vector<Future<Result>>
227 window(Collection input, F func, size_t n);
229 template <typename F, typename T, typename ItT>
230 using MaybeTryArg = typename std::conditional<
231 detail::callableWith<F, T&&, Try<ItT>&&>::value, Try<ItT>, ItT>::type;
233 template<typename F, typename T, typename Arg>
234 using isFutureResult = isFuture<typename std::result_of<F(T&&, Arg&&)>::type>;
236 /** repeatedly calls func on every result, e.g.
237 reduce(reduce(reduce(T initial, result of first), result of second), ...)
239 The type of the final result is a Future of the type of the initial value.
241 Func can either return a T, or a Future<T>
243 func is called in order of the input, see unorderedReduce if that is not
246 template <class It, class T, class F>
247 Future<T> reduce(It first, It last, T&& initial, F&& func);
249 /// Sugar for the most common case
250 template <class Collection, class T, class F>
251 auto reduce(Collection&& c, T&& initial, F&& func)
252 -> decltype(reduce(c.begin(), c.end(), std::forward<T>(initial),
253 std::forward<F>(func))) {
257 std::forward<T>(initial),
258 std::forward<F>(func));
261 /** like reduce, but calls func on finished futures as they complete
262 does NOT keep the order of the input
264 template <class It, class T, class F,
265 class ItT = typename std::iterator_traits<It>::value_type::value_type,
266 class Arg = MaybeTryArg<F, T, ItT>>
267 Future<T> unorderedReduce(It first, It last, T initial, F func);
269 /// Sugar for the most common case
270 template <class Collection, class T, class F>
271 auto unorderedReduce(Collection&& c, T&& initial, F&& func)
272 -> decltype(unorderedReduce(c.begin(), c.end(), std::forward<T>(initial),
273 std::forward<F>(func))) {
274 return unorderedReduce(
277 std::forward<T>(initial),
278 std::forward<F>(func));