2 * Copyright 2017 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.
22 #include <folly/Portability.h>
23 #include <folly/Try.h>
24 #include <folly/futures/Future.h>
25 #include <folly/futures/Promise.h>
31 template <typename... Ts>
32 struct CollectAllVariadicContext {
33 CollectAllVariadicContext() {}
34 template <typename T, size_t I>
35 inline void setPartialResult(Try<T>& t) {
36 std::get<I>(results) = std::move(t);
38 ~CollectAllVariadicContext() {
39 p.setValue(std::move(results));
41 Promise<std::tuple<Try<Ts>...>> p;
42 std::tuple<Try<Ts>...> results;
43 typedef Future<std::tuple<Try<Ts>...>> type;
46 template <typename... Ts>
47 struct CollectVariadicContext {
48 CollectVariadicContext() {}
49 template <typename T, size_t I>
50 inline void setPartialResult(Try<T>& t) {
51 if (t.hasException()) {
52 if (!threw.exchange(true)) {
53 p.setException(std::move(t.exception()));
56 std::get<I>(results) = std::move(t);
59 ~CollectVariadicContext() noexcept {
60 if (!threw.exchange(true)) {
61 p.setValue(unwrapTryTuple(std::move(results)));
64 Promise<std::tuple<Ts...>> p;
65 std::tuple<folly::Try<Ts>...> results;
66 std::atomic<bool> threw{false};
67 typedef Future<std::tuple<Ts...>> type;
70 } // namespace futures
72 /// This namespace is for utility functions that would usually be static
73 /// members of Future, except they don't make sense there because they don't
74 /// depend on the template type (rather, on the type of their arguments in
75 /// some cases). This is the least-bad naming scheme we could think of. Some
76 /// of the functions herein have really-likely-to-collide names, like "map"
79 /// Returns a Future that will complete after the specified duration. The
80 /// Duration typedef of a `std::chrono` duration type indicates the
81 /// resolution you can expect to be meaningful (milliseconds at the time of
82 /// writing). Normally you wouldn't need to specify a Timekeeper, we will
83 /// use the global futures timekeeper (we run a thread whose job it is to
84 /// keep time for futures timeouts) but we provide the option for power
87 /// The Timekeeper thread will be lazily created the first time it is
88 /// needed. If your program never uses any timeouts or other time-based
89 /// Futures you will pay no Timekeeper thread overhead.
90 Future<Unit> sleep(Duration, Timekeeper* = nullptr);
93 * Set func as the callback for each input Future and return a vector of
94 * Futures containing the results in the input order.
99 class ItT = typename std::iterator_traits<It>::value_type,
100 class Result = typename decltype(
101 std::declval<ItT>().then(std::declval<F>()))::value_type>
102 std::vector<Future<Result>> map(It first, It last, F func);
104 // Sugar for the most common case
105 template <class Collection, class F>
106 auto map(Collection&& c, F&& func)
107 -> decltype(map(c.begin(), c.end(), func)) {
108 return map(c.begin(), c.end(), std::forward<F>(func));
111 } // namespace futures
114 Make a completed Future by moving in a value. e.g.
117 auto f = makeFuture(std::move(foo));
121 auto f = makeFuture<string>("foo");
124 Future<typename std::decay<T>::type> makeFuture(T&& t);
126 /** Make a completed void Future. */
127 Future<Unit> makeFuture();
130 Make a Future by executing a function.
132 If the function returns a value of type T, makeFutureWith
133 returns a completed Future<T>, capturing the value returned
136 If the function returns a Future<T> already, makeFutureWith
139 Either way, if the function throws, a failed Future is
140 returned that captures the exception.
142 Calling makeFutureWith(func) is equivalent to calling
143 makeFuture().then(func).
146 // makeFutureWith(Future<T>()) -> Future<T>
148 typename std::enable_if<isFuture<typename std::result_of<F()>::type>::value,
149 typename std::result_of<F()>::type>::type
150 makeFutureWith(F&& func);
152 // makeFutureWith(T()) -> Future<T>
153 // makeFutureWith(void()) -> Future<Unit>
155 typename std::enable_if<
156 !(isFuture<typename std::result_of<F()>::type>::value),
157 Future<typename Unit::Lift<typename std::result_of<F()>::type>::type>>::type
158 makeFutureWith(F&& func);
160 /// Make a failed Future from an exception_ptr.
161 /// Because the Future's type cannot be inferred you have to specify it, e.g.
163 /// auto f = makeFuture<string>(std::current_exception());
165 FOLLY_DEPRECATED("use makeFuture(exception_wrapper)")
166 Future<T> makeFuture(std::exception_ptr const& e);
168 /// Make a failed Future from an exception_wrapper.
170 Future<T> makeFuture(exception_wrapper ew);
172 /** Make a Future from an exception type E that can be passed to
173 std::make_exception_ptr(). */
174 template <class T, class E>
175 typename std::enable_if<std::is_base_of<std::exception, E>::value,
177 makeFuture(E const& e);
179 /** Make a Future out of a Try */
181 Future<T> makeFuture(Try<T>&& t);
184 * Return a new Future that will call back on the given Executor.
185 * This is just syntactic sugar for makeFuture().via(executor)
187 * @param executor the Executor to call back on
188 * @param priority optionally, the priority to add with. Defaults to 0 which
189 * represents medium priority.
191 * @returns a void Future that will call back on the given executor
193 inline Future<Unit> via(
195 int8_t priority = Executor::MID_PRI);
197 /// Execute a function via the given executor and return a future.
198 /// This is semantically equivalent to via(executor).then(func), but
199 /// easier to read and slightly more efficient.
200 template <class Func>
201 auto via(Executor*, Func&& func)
202 -> Future<typename isFuture<decltype(std::declval<Func>()())>::Inner>;
204 /** When all the input Futures complete, the returned Future will complete.
205 Errors do not cause early termination; this Future will always succeed
206 after all its Futures have finished (whether successfully or with an
209 The Futures are moved in, so your copies are invalid. If you need to
210 chain further from these Futures, use the variant with an output iterator.
212 This function is thread-safe for Futures running on different threads. But
213 if you are doing anything non-trivial after, you will probably want to
214 follow with `via(executor)` because it will complete in whichever thread the
215 last Future completes in.
217 The return type for Future<T> input is a Future<std::vector<Try<T>>>
219 template <class InputIterator>
220 Future<std::vector<Try<
221 typename std::iterator_traits<InputIterator>::value_type::value_type>>>
222 collectAll(InputIterator first, InputIterator last);
224 /// Sugar for the most common case
225 template <class Collection>
226 auto collectAll(Collection&& c) -> decltype(collectAll(c.begin(), c.end())) {
227 return collectAll(c.begin(), c.end());
230 /// This version takes a varying number of Futures instead of an iterator.
231 /// The return type for (Future<T1>, Future<T2>, ...) input
232 /// is a Future<std::tuple<Try<T1>, Try<T2>, ...>>.
233 /// The Futures are moved in, so your copies are invalid.
234 template <typename... Fs>
235 typename futures::detail::CollectAllVariadicContext<
236 typename std::decay<Fs>::type::value_type...>::type
237 collectAll(Fs&&... fs);
239 /// Like collectAll, but will short circuit on the first exception. Thus, the
240 /// type of the returned Future is std::vector<T> instead of
241 /// std::vector<Try<T>>
242 template <class InputIterator>
243 Future<typename futures::detail::CollectContext<typename std::iterator_traits<
244 InputIterator>::value_type::value_type>::result_type>
245 collect(InputIterator first, InputIterator last);
247 /// Sugar for the most common case
248 template <class Collection>
249 auto collect(Collection&& c) -> decltype(collect(c.begin(), c.end())) {
250 return collect(c.begin(), c.end());
253 /// Like collectAll, but will short circuit on the first exception. Thus, the
254 /// type of the returned Future is std::tuple<T1, T2, ...> instead of
255 /// std::tuple<Try<T1>, Try<T2>, ...>
256 template <typename... Fs>
257 typename futures::detail::CollectVariadicContext<
258 typename std::decay<Fs>::type::value_type...>::type
261 /** The result is a pair of the index of the first Future to complete and
262 the Try. If multiple Futures complete at the same time (or are already
263 complete when passed in), the "winner" is chosen non-deterministically.
265 This function is thread-safe for Futures running on different threads.
267 template <class InputIterator>
270 Try<typename std::iterator_traits<InputIterator>::value_type::value_type>>>
271 collectAny(InputIterator first, InputIterator last);
273 /// Sugar for the most common case
274 template <class Collection>
275 auto collectAny(Collection&& c) -> decltype(collectAny(c.begin(), c.end())) {
276 return collectAny(c.begin(), c.end());
279 /** Similar to collectAny, collectAnyWithoutException return the first Future to
280 * complete without exceptions. If none of the future complete without
281 * excpetions, the last exception will be returned as a result.
283 template <class InputIterator>
286 typename std::iterator_traits<InputIterator>::value_type::value_type>>
287 collectAnyWithoutException(InputIterator first, InputIterator last);
289 /// Sugar for the most common case
290 template <class Collection>
291 auto collectAnyWithoutException(Collection&& c)
292 -> decltype(collectAnyWithoutException(c.begin(), c.end())) {
293 return collectAnyWithoutException(c.begin(), c.end());
296 /** when n Futures have completed, the Future completes with a vector of
297 the index and Try of those n Futures (the indices refer to the original
298 order, but the result vector will be in an arbitrary order)
302 template <class InputIterator>
303 Future<std::vector<std::pair<
305 Try<typename std::iterator_traits<InputIterator>::value_type::value_type>>>>
306 collectN(InputIterator first, InputIterator last, size_t n);
308 /// Sugar for the most common case
309 template <class Collection>
310 auto collectN(Collection&& c, size_t n)
311 -> decltype(collectN(c.begin(), c.end(), n)) {
312 return collectN(c.begin(), c.end(), n);
315 /** window creates up to n Futures using the values
316 in the collection, and then another Future for each Future
319 this is basically a sliding window of Futures of size n
321 func must return a Future for each value in input
326 class ItT = typename std::iterator_traits<
327 typename Collection::iterator>::value_type,
328 class Result = typename futures::detail::resultOf<F, ItT&&>::value_type>
329 std::vector<Future<Result>> window(Collection input, F func, size_t n);
331 template <typename F, typename T, typename ItT>
332 using MaybeTryArg = typename std::conditional<
333 futures::detail::callableWith<F, T&&, Try<ItT>&&>::value,
337 template <typename F, typename T, typename Arg>
338 using isFutureResult = isFuture<typename std::result_of<F(T&&, Arg&&)>::type>;
340 /** repeatedly calls func on every result, e.g.
341 reduce(reduce(reduce(T initial, result of first), result of second), ...)
343 The type of the final result is a Future of the type of the initial value.
345 Func can either return a T, or a Future<T>
347 func is called in order of the input, see unorderedReduce if that is not
350 template <class It, class T, class F>
351 Future<T> reduce(It first, It last, T&& initial, F&& func);
353 /// Sugar for the most common case
354 template <class Collection, class T, class F>
355 auto reduce(Collection&& c, T&& initial, F&& func)
356 -> decltype(reduce(c.begin(), c.end(), std::forward<T>(initial),
357 std::forward<F>(func))) {
361 std::forward<T>(initial),
362 std::forward<F>(func));
365 /** like reduce, but calls func on finished futures as they complete
366 does NOT keep the order of the input
372 class ItT = typename std::iterator_traits<It>::value_type::value_type,
373 class Arg = MaybeTryArg<F, T, ItT>>
374 Future<T> unorderedReduce(It first, It last, T initial, F func);
376 /// Sugar for the most common case
377 template <class Collection, class T, class F>
378 auto unorderedReduce(Collection&& c, T&& initial, F&& func)
379 -> decltype(unorderedReduce(c.begin(), c.end(), std::forward<T>(initial),
380 std::forward<F>(func))) {
381 return unorderedReduce(
384 std::forward<T>(initial),
385 std::forward<F>(func));