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 SemiFuture by moving in a value. e.g.
117 auto f = makeSemiFuture(std::move(foo));
121 auto f = makeSemiFuture<string>("foo");
124 SemiFuture<typename std::decay<T>::type> makeSemiFuture(T&& t);
126 /** Make a completed void SemiFuture. */
127 SemiFuture<Unit> makeSemiFuture();
130 Make a SemiFuture by executing a function.
132 If the function returns a value of type T, makeSemiFutureWith
133 returns a completed SemiFuture<T>, capturing the value returned
136 If the function returns a SemiFuture<T> already, makeSemiFutureWith
139 Either way, if the function throws, a failed Future is
140 returned that captures the exception.
143 // makeSemiFutureWith(SemiFuture<T>()) -> SemiFuture<T>
145 typename std::enable_if<isSemiFuture<typename std::result_of<F()>::type>::value,
146 typename std::result_of<F()>::type>::type
147 makeSemiFutureWith(F&& func);
149 // makeSemiFutureWith(T()) -> SemiFuture<T>
150 // makeSemiFutureWith(void()) -> SemiFuture<Unit>
152 typename std::enable_if<
153 !(isSemiFuture<typename std::result_of<F()>::type>::value),
154 SemiFuture<typename Unit::Lift<typename std::result_of<F()>::type>::type>>::type
155 makeSemiFutureWith(F&& func);
157 /// Make a failed Future from an exception_ptr.
158 /// Because the Future's type cannot be inferred you have to specify it, e.g.
160 /// auto f = makeSemiFuture<string>(std::current_exception());
162 FOLLY_DEPRECATED("use makeSemiFuture(exception_wrapper)")
163 SemiFuture<T> makeSemiFuture(std::exception_ptr const& e);
165 /// Make a failed SemiFuture from an exception_wrapper.
167 SemiFuture<T> makeSemiFuture(exception_wrapper ew);
169 /** Make a SemiFuture from an exception type E that can be passed to
170 std::make_exception_ptr(). */
171 template <class T, class E>
172 typename std::enable_if<std::is_base_of<std::exception, E>::value,
174 makeSemiFuture(E const& e);
176 /** Make a Future out of a Try */
178 SemiFuture<T> makeSemiFuture(Try<T>&& t);
181 Make a completed Future by moving in a value. e.g.
184 auto f = makeFuture(std::move(foo));
188 auto f = makeFuture<string>("foo");
190 NOTE: This function is deprecated. Please use makeSemiFuture and pass the
191 appropriate executor to .via on the returned SemiFuture to get a
192 valid Future where necessary.
195 Future<typename std::decay<T>::type> makeFuture(T&& t);
198 Make a completed void Future.
200 NOTE: This function is deprecated. Please use makeSemiFuture and pass the
201 appropriate executor to .via on the returned SemiFuture to get a
202 valid Future where necessary.
204 Future<Unit> makeFuture();
207 Make a Future by executing a function.
209 If the function returns a value of type T, makeFutureWith
210 returns a completed Future<T>, capturing the value returned
213 If the function returns a Future<T> already, makeFutureWith
216 Either way, if the function throws, a failed Future is
217 returned that captures the exception.
219 Calling makeFutureWith(func) is equivalent to calling
220 makeFuture().then(func).
222 NOTE: This function is deprecated. Please use makeSemiFutureWith and pass the
223 appropriate executor to .via on the returned SemiFuture to get a
224 valid Future where necessary.
227 // makeFutureWith(Future<T>()) -> Future<T>
229 typename std::enable_if<isFuture<typename std::result_of<F()>::type>::value,
230 typename std::result_of<F()>::type>::type
231 makeFutureWith(F&& func);
233 // makeFutureWith(T()) -> Future<T>
234 // makeFutureWith(void()) -> Future<Unit>
236 typename std::enable_if<
237 !(isFuture<typename std::result_of<F()>::type>::value),
238 Future<typename Unit::Lift<typename std::result_of<F()>::type>::type>>::type
239 makeFutureWith(F&& func);
241 /// Make a failed Future from an exception_ptr.
242 /// Because the Future's type cannot be inferred you have to specify it, e.g.
244 /// auto f = makeFuture<string>(std::current_exception());
246 FOLLY_DEPRECATED("use makeSemiFuture(exception_wrapper)")
247 Future<T> makeFuture(std::exception_ptr const& e);
249 /// Make a failed Future from an exception_wrapper.
250 /// NOTE: This function is deprecated. Please use makeSemiFuture and pass the
251 /// appropriate executor to .via on the returned SemiFuture to get a
252 /// valid Future where necessary.
254 Future<T> makeFuture(exception_wrapper ew);
256 /** Make a Future from an exception type E that can be passed to
257 std::make_exception_ptr().
259 NOTE: This function is deprecated. Please use makeSemiFuture and pass the
260 appropriate executor to .via on the returned SemiFuture to get a
261 valid Future where necessary.
263 template <class T, class E>
264 typename std::enable_if<std::is_base_of<std::exception, E>::value,
266 makeFuture(E const& e);
269 Make a Future out of a Try
271 NOTE: This function is deprecated. Please use makeSemiFuture and pass the
272 appropriate executor to .via on the returned SemiFuture to get a
273 valid Future where necessary.
276 Future<T> makeFuture(Try<T>&& t);
279 * Return a new Future that will call back on the given Executor.
280 * This is just syntactic sugar for makeFuture().via(executor)
282 * @param executor the Executor to call back on
283 * @param priority optionally, the priority to add with. Defaults to 0 which
284 * represents medium priority.
286 * @returns a void Future that will call back on the given executor
288 inline Future<Unit> via(
290 int8_t priority = Executor::MID_PRI);
292 /// Execute a function via the given executor and return a future.
293 /// This is semantically equivalent to via(executor).then(func), but
294 /// easier to read and slightly more efficient.
295 template <class Func>
296 auto via(Executor*, Func&& func)
297 -> Future<typename isFuture<decltype(std::declval<Func>()())>::Inner>;
299 /** When all the input Futures complete, the returned Future will complete.
300 Errors do not cause early termination; this Future will always succeed
301 after all its Futures have finished (whether successfully or with an
304 The Futures are moved in, so your copies are invalid. If you need to
305 chain further from these Futures, use the variant with an output iterator.
307 This function is thread-safe for Futures running on different threads. But
308 if you are doing anything non-trivial after, you will probably want to
309 follow with `via(executor)` because it will complete in whichever thread the
310 last Future completes in.
312 The return type for Future<T> input is a Future<std::vector<Try<T>>>
314 template <class InputIterator>
315 Future<std::vector<Try<
316 typename std::iterator_traits<InputIterator>::value_type::value_type>>>
317 collectAll(InputIterator first, InputIterator last);
319 /// Sugar for the most common case
320 template <class Collection>
321 auto collectAll(Collection&& c) -> decltype(collectAll(c.begin(), c.end())) {
322 return collectAll(c.begin(), c.end());
325 /// This version takes a varying number of Futures instead of an iterator.
326 /// The return type for (Future<T1>, Future<T2>, ...) input
327 /// is a Future<std::tuple<Try<T1>, Try<T2>, ...>>.
328 /// The Futures are moved in, so your copies are invalid.
329 template <typename... Fs>
330 typename futures::detail::CollectAllVariadicContext<
331 typename std::decay<Fs>::type::value_type...>::type
332 collectAll(Fs&&... fs);
334 /// Like collectAll, but will short circuit on the first exception. Thus, the
335 /// type of the returned Future is std::vector<T> instead of
336 /// std::vector<Try<T>>
337 template <class InputIterator>
338 Future<typename futures::detail::CollectContext<typename std::iterator_traits<
339 InputIterator>::value_type::value_type>::result_type>
340 collect(InputIterator first, InputIterator last);
342 /// Sugar for the most common case
343 template <class Collection>
344 auto collect(Collection&& c) -> decltype(collect(c.begin(), c.end())) {
345 return collect(c.begin(), c.end());
348 /// Like collectAll, but will short circuit on the first exception. Thus, the
349 /// type of the returned Future is std::tuple<T1, T2, ...> instead of
350 /// std::tuple<Try<T1>, Try<T2>, ...>
351 template <typename... Fs>
352 typename futures::detail::CollectVariadicContext<
353 typename std::decay<Fs>::type::value_type...>::type
356 /** The result is a pair of the index of the first Future to complete and
357 the Try. If multiple Futures complete at the same time (or are already
358 complete when passed in), the "winner" is chosen non-deterministically.
360 This function is thread-safe for Futures running on different threads.
362 template <class InputIterator>
365 Try<typename std::iterator_traits<InputIterator>::value_type::value_type>>>
366 collectAny(InputIterator first, InputIterator last);
368 /// Sugar for the most common case
369 template <class Collection>
370 auto collectAny(Collection&& c) -> decltype(collectAny(c.begin(), c.end())) {
371 return collectAny(c.begin(), c.end());
374 /** Similar to collectAny, collectAnyWithoutException return the first Future to
375 * complete without exceptions. If none of the future complete without
376 * excpetions, the last exception will be returned as a result.
378 template <class InputIterator>
381 typename std::iterator_traits<InputIterator>::value_type::value_type>>
382 collectAnyWithoutException(InputIterator first, InputIterator last);
384 /// Sugar for the most common case
385 template <class Collection>
386 auto collectAnyWithoutException(Collection&& c)
387 -> decltype(collectAnyWithoutException(c.begin(), c.end())) {
388 return collectAnyWithoutException(c.begin(), c.end());
391 /** when n Futures have completed, the Future completes with a vector of
392 the index and Try of those n Futures (the indices refer to the original
393 order, but the result vector will be in an arbitrary order)
397 template <class InputIterator>
398 Future<std::vector<std::pair<
400 Try<typename std::iterator_traits<InputIterator>::value_type::value_type>>>>
401 collectN(InputIterator first, InputIterator last, size_t n);
403 /// Sugar for the most common case
404 template <class Collection>
405 auto collectN(Collection&& c, size_t n)
406 -> decltype(collectN(c.begin(), c.end(), n)) {
407 return collectN(c.begin(), c.end(), n);
410 /** window creates up to n Futures using the values
411 in the collection, and then another Future for each Future
414 this is basically a sliding window of Futures of size n
416 func must return a Future for each value in input
421 class ItT = typename std::iterator_traits<
422 typename Collection::iterator>::value_type,
423 class Result = typename futures::detail::resultOf<F, ItT&&>::value_type>
424 std::vector<Future<Result>> window(Collection input, F func, size_t n);
429 class ItT = typename std::iterator_traits<
430 typename Collection::iterator>::value_type,
431 class Result = typename futures::detail::resultOf<F, ItT&&>::value_type>
432 std::vector<Future<Result>>
433 window(Executor* executor, Collection input, F func, size_t n);
435 template <typename F, typename T, typename ItT>
436 using MaybeTryArg = typename std::conditional<
437 futures::detail::callableWith<F, T&&, Try<ItT>&&>::value,
441 template <typename F, typename T, typename Arg>
442 using isFutureResult = isFuture<typename std::result_of<F(T&&, Arg&&)>::type>;
444 /** repeatedly calls func on every result, e.g.
445 reduce(reduce(reduce(T initial, result of first), result of second), ...)
447 The type of the final result is a Future of the type of the initial value.
449 Func can either return a T, or a Future<T>
451 func is called in order of the input, see unorderedReduce if that is not
454 template <class It, class T, class F>
455 Future<T> reduce(It first, It last, T&& initial, F&& func);
457 /// Sugar for the most common case
458 template <class Collection, class T, class F>
459 auto reduce(Collection&& c, T&& initial, F&& func)
460 -> decltype(reduce(c.begin(), c.end(), std::forward<T>(initial),
461 std::forward<F>(func))) {
465 std::forward<T>(initial),
466 std::forward<F>(func));
469 /** like reduce, but calls func on finished futures as they complete
470 does NOT keep the order of the input
476 class ItT = typename std::iterator_traits<It>::value_type::value_type,
477 class Arg = MaybeTryArg<F, T, ItT>>
478 Future<T> unorderedReduce(It first, It last, T initial, F func);
480 /// Sugar for the most common case
481 template <class Collection, class T, class F>
482 auto unorderedReduce(Collection&& c, T&& initial, F&& func)
483 -> decltype(unorderedReduce(c.begin(), c.end(), std::forward<T>(initial),
484 std::forward<F>(func))) {
485 return unorderedReduce(
488 std::forward<T>(initial),
489 std::forward<F>(func));