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.
24 #include <folly/Baton.h>
25 #include <folly/Optional.h>
26 #include <folly/Random.h>
27 #include <folly/Traits.h>
28 #include <folly/futures/detail/Core.h>
29 #include <folly/futures/Timekeeper.h>
31 #if defined(__ANDROID__) || defined(__APPLE__)
32 #define FOLLY_FUTURE_USING_FIBER 0
34 #define FOLLY_FUTURE_USING_FIBER 1
35 #include <folly/experimental/fibers/Baton.h>
43 #if FOLLY_FUTURE_USING_FIBER
44 typedef folly::fibers::Baton FutureBatonType;
46 typedef folly::Baton<> FutureBatonType;
51 std::shared_ptr<Timekeeper> getTimekeeperSingleton();
55 Future<T>::Future(Future<T>&& other) noexcept : core_(other.core_) {
56 other.core_ = nullptr;
60 Future<T>& Future<T>::operator=(Future<T>&& other) noexcept {
61 std::swap(core_, other.core_);
66 template <class T2, typename>
67 Future<T>::Future(T2&& val)
68 : core_(new detail::Core<T>(Try<T>(std::forward<T2>(val)))) {}
71 template <typename, typename>
73 : core_(new detail::Core<T>(Try<T>(T()))) {}
76 Future<T>::~Future() {
81 void Future<T>::detach() {
83 core_->detachFuture();
89 void Future<T>::throwIfInvalid() const {
96 void Future<T>::setCallback_(F&& func) {
98 core_->setCallback(std::move(func));
105 typename std::enable_if<isFuture<F>::value,
106 Future<typename isFuture<T>::Inner>>::type
107 Future<T>::unwrap() {
108 return then([](Future<typename isFuture<T>::Inner> internal_future) {
109 return internal_future;
115 // Variant: returns a value
116 // e.g. f.then([](Try<T>&& t){ return t.value(); });
118 template <typename F, typename R, bool isTry, typename... Args>
119 typename std::enable_if<!R::ReturnsFuture::value, typename R::Return>::type
120 Future<T>::thenImplementation(F func, detail::argResult<isTry, F, Args...>) {
121 static_assert(sizeof...(Args) <= 1, "Then must take zero/one argument");
122 typedef typename R::ReturnsFuture::Inner B;
126 // wrap these so we can move them into the lambda
127 folly::MoveWrapper<Promise<B>> p;
128 p->core_->setInterruptHandlerNoLock(core_->getInterruptHandler());
129 folly::MoveWrapper<F> funcm(std::forward<F>(func));
131 // grab the Future now before we lose our handle on the Promise
132 auto f = p->getFuture();
133 f.core_->setExecutorNoLock(getExecutor());
135 /* This is a bit tricky.
137 We can't just close over *this in case this Future gets moved. So we
138 make a new dummy Future. We could figure out something more
139 sophisticated that avoids making a new Future object when it can, as an
140 optimization. But this is correct.
142 core_ can't be moved, it is explicitly disallowed (as is copying). But
143 if there's ever a reason to allow it, this is one place that makes that
144 assumption and would need to be fixed. We use a standard shared pointer
145 for core_ (by copying it in), which means in essence obj holds a shared
146 pointer to itself. But this shouldn't leak because Promise will not
147 outlive the continuation, because Promise will setException() with a
148 broken Promise if it is destructed before completed. We could use a
149 weak pointer but it would have to be converted to a shared pointer when
150 func is executed (because the Future returned by func may possibly
151 persist beyond the callback, if it gets moved), and so it is an
152 optimization to just make it shared from the get-go.
154 We have to move in the Promise and func using the MoveWrapper
155 hack. (func could be copied but it's a big drag on perf).
157 Two subtle but important points about this design. detail::Core has no
158 back pointers to Future or Promise, so if Future or Promise get moved
159 (and they will be moved in performant code) we don't have to do
160 anything fancy. And because we store the continuation in the
161 detail::Core, not in the Future, we can execute the continuation even
162 after the Future has gone out of scope. This is an intentional design
163 decision. It is likely we will want to be able to cancel a continuation
164 in some circumstances, but I think it should be explicit not implicit
165 in the destruction of the Future used to create it.
168 [p, funcm](Try<T>&& t) mutable {
169 if (!isTry && t.hasException()) {
170 p->setException(std::move(t.exception()));
173 return (*funcm)(t.template get<isTry, Args>()...);
181 // Variant: returns a Future
182 // e.g. f.then([](T&& t){ return makeFuture<T>(t); });
184 template <typename F, typename R, bool isTry, typename... Args>
185 typename std::enable_if<R::ReturnsFuture::value, typename R::Return>::type
186 Future<T>::thenImplementation(F func, detail::argResult<isTry, F, Args...>) {
187 static_assert(sizeof...(Args) <= 1, "Then must take zero/one argument");
188 typedef typename R::ReturnsFuture::Inner B;
192 // wrap these so we can move them into the lambda
193 folly::MoveWrapper<Promise<B>> p;
194 p->core_->setInterruptHandlerNoLock(core_->getInterruptHandler());
195 folly::MoveWrapper<F> funcm(std::forward<F>(func));
197 // grab the Future now before we lose our handle on the Promise
198 auto f = p->getFuture();
199 f.core_->setExecutorNoLock(getExecutor());
202 [p, funcm](Try<T>&& t) mutable {
203 if (!isTry && t.hasException()) {
204 p->setException(std::move(t.exception()));
207 auto f2 = (*funcm)(t.template get<isTry, Args>()...);
208 // that didn't throw, now we can steal p
209 f2.setCallback_([p](Try<B>&& b) mutable {
210 p->setTry(std::move(b));
212 } catch (const std::exception& e) {
213 p->setException(exception_wrapper(std::current_exception(), e));
215 p->setException(exception_wrapper(std::current_exception()));
223 template <typename T>
224 template <typename R, typename Caller, typename... Args>
225 Future<typename isFuture<R>::Inner>
226 Future<T>::then(R(Caller::*func)(Args...), Caller *instance) {
227 typedef typename std::remove_cv<
228 typename std::remove_reference<
229 typename detail::ArgType<Args...>::FirstArg>::type>::type FirstArg;
230 return then([instance, func](Try<T>&& t){
231 return (instance->*func)(t.template get<isTry<FirstArg>::value, Args>()...);
236 template <class Executor, class Arg, class... Args>
237 auto Future<T>::then(Executor* x, Arg&& arg, Args&&... args)
238 -> decltype(this->then(std::forward<Arg>(arg),
239 std::forward<Args>(args)...))
241 auto oldX = getExecutor();
243 return this->then(std::forward<Arg>(arg), std::forward<Args>(args)...).
248 Future<Unit> Future<T>::then() {
249 return then([] () {});
252 // onError where the callback returns T
255 typename std::enable_if<
256 !detail::callableWith<F, exception_wrapper>::value &&
257 !detail::Extract<F>::ReturnsFuture::value,
259 Future<T>::onError(F&& func) {
260 typedef typename detail::Extract<F>::FirstArg Exn;
262 std::is_same<typename detail::Extract<F>::RawReturn, T>::value,
263 "Return type of onError callback must be T or Future<T>");
266 p.core_->setInterruptHandlerNoLock(core_->getInterruptHandler());
267 auto f = p.getFuture();
268 auto pm = folly::makeMoveWrapper(std::move(p));
269 auto funcm = folly::makeMoveWrapper(std::move(func));
270 setCallback_([pm, funcm](Try<T>&& t) mutable {
271 if (!t.template withException<Exn>([&] (Exn& e) {
276 pm->setTry(std::move(t));
283 // onError where the callback returns Future<T>
286 typename std::enable_if<
287 !detail::callableWith<F, exception_wrapper>::value &&
288 detail::Extract<F>::ReturnsFuture::value,
290 Future<T>::onError(F&& func) {
292 std::is_same<typename detail::Extract<F>::Return, Future<T>>::value,
293 "Return type of onError callback must be T or Future<T>");
294 typedef typename detail::Extract<F>::FirstArg Exn;
297 auto f = p.getFuture();
298 auto pm = folly::makeMoveWrapper(std::move(p));
299 auto funcm = folly::makeMoveWrapper(std::move(func));
300 setCallback_([pm, funcm](Try<T>&& t) mutable {
301 if (!t.template withException<Exn>([&] (Exn& e) {
303 auto f2 = (*funcm)(e);
304 f2.setCallback_([pm](Try<T>&& t2) mutable {
305 pm->setTry(std::move(t2));
307 } catch (const std::exception& e2) {
308 pm->setException(exception_wrapper(std::current_exception(), e2));
310 pm->setException(exception_wrapper(std::current_exception()));
313 pm->setTry(std::move(t));
322 Future<T> Future<T>::ensure(F func) {
323 MoveWrapper<F> funcw(std::move(func));
324 return this->then([funcw](Try<T>&& t) mutable {
326 return makeFuture(std::move(t));
332 Future<T> Future<T>::onTimeout(Duration dur, F&& func, Timekeeper* tk) {
333 auto funcw = folly::makeMoveWrapper(std::forward<F>(func));
334 return within(dur, tk)
335 .onError([funcw](TimedOut const&) { return (*funcw)(); });
340 typename std::enable_if<
341 detail::callableWith<F, exception_wrapper>::value &&
342 detail::Extract<F>::ReturnsFuture::value,
344 Future<T>::onError(F&& func) {
346 std::is_same<typename detail::Extract<F>::Return, Future<T>>::value,
347 "Return type of onError callback must be T or Future<T>");
350 auto f = p.getFuture();
351 auto pm = folly::makeMoveWrapper(std::move(p));
352 auto funcm = folly::makeMoveWrapper(std::move(func));
353 setCallback_([pm, funcm](Try<T> t) mutable {
354 if (t.hasException()) {
356 auto f2 = (*funcm)(std::move(t.exception()));
357 f2.setCallback_([pm](Try<T> t2) mutable {
358 pm->setTry(std::move(t2));
360 } catch (const std::exception& e2) {
361 pm->setException(exception_wrapper(std::current_exception(), e2));
363 pm->setException(exception_wrapper(std::current_exception()));
366 pm->setTry(std::move(t));
373 // onError(exception_wrapper) that returns T
376 typename std::enable_if<
377 detail::callableWith<F, exception_wrapper>::value &&
378 !detail::Extract<F>::ReturnsFuture::value,
380 Future<T>::onError(F&& func) {
382 std::is_same<typename detail::Extract<F>::Return, Future<T>>::value,
383 "Return type of onError callback must be T or Future<T>");
386 auto f = p.getFuture();
387 auto pm = folly::makeMoveWrapper(std::move(p));
388 auto funcm = folly::makeMoveWrapper(std::move(func));
389 setCallback_([pm, funcm](Try<T> t) mutable {
390 if (t.hasException()) {
392 return (*funcm)(std::move(t.exception()));
395 pm->setTry(std::move(t));
403 typename std::add_lvalue_reference<T>::type Future<T>::value() {
406 return core_->getTry().value();
410 typename std::add_lvalue_reference<const T>::type Future<T>::value() const {
413 return core_->getTry().value();
417 Try<T>& Future<T>::getTry() {
420 return core_->getTry();
424 Optional<Try<T>> Future<T>::poll() {
426 if (core_->ready()) {
427 o = std::move(core_->getTry());
433 inline Future<T> Future<T>::via(Executor* executor, int8_t priority) && {
436 setExecutor(executor, priority);
438 return std::move(*this);
442 inline Future<T> Future<T>::via(Executor* executor, int8_t priority) & {
445 MoveWrapper<Promise<T>> p;
446 auto f = p->getFuture();
447 then([p](Try<T>&& t) mutable { p->setTry(std::move(t)); });
448 return std::move(f).via(executor, priority);
452 template <class Func>
453 auto via(Executor* x, Func func)
454 -> Future<typename isFuture<decltype(func())>::Inner>
456 // TODO make this actually more performant. :-P #7260175
457 return via(x).then(func);
461 bool Future<T>::isReady() const {
463 return core_->ready();
467 bool Future<T>::hasValue() {
468 return getTry().hasValue();
472 bool Future<T>::hasException() {
473 return getTry().hasException();
477 void Future<T>::raise(exception_wrapper exception) {
478 core_->raise(std::move(exception));
484 Future<typename std::decay<T>::type> makeFuture(T&& t) {
485 return makeFuture(Try<typename std::decay<T>::type>(std::forward<T>(t)));
488 inline // for multiple translation units
489 Future<Unit> makeFuture() {
490 return makeFuture(Unit{});
493 // makeFutureWith(Future<T>()) -> Future<T>
495 typename std::enable_if<isFuture<typename std::result_of<F()>::type>::value,
496 typename std::result_of<F()>::type>::type
497 makeFutureWith(F&& func) {
499 typename isFuture<typename std::result_of<F()>::type>::Inner;
502 } catch (std::exception& e) {
503 return makeFuture<InnerType>(
504 exception_wrapper(std::current_exception(), e));
506 return makeFuture<InnerType>(exception_wrapper(std::current_exception()));
510 // makeFutureWith(T()) -> Future<T>
511 // makeFutureWith(void()) -> Future<Unit>
513 typename std::enable_if<
514 !(isFuture<typename std::result_of<F()>::type>::value),
515 Future<typename Unit::Lift<typename std::result_of<F()>::type>::type>>::type
516 makeFutureWith(F&& func) {
518 typename Unit::Lift<typename std::result_of<F()>::type>::type;
519 return makeFuture<LiftedResult>(makeTryWith([&func]() mutable {
525 Future<T> makeFuture(std::exception_ptr const& e) {
526 return makeFuture(Try<T>(e));
530 Future<T> makeFuture(exception_wrapper ew) {
531 return makeFuture(Try<T>(std::move(ew)));
534 template <class T, class E>
535 typename std::enable_if<std::is_base_of<std::exception, E>::value,
537 makeFuture(E const& e) {
538 return makeFuture(Try<T>(make_exception_wrapper<E>(e)));
542 Future<T> makeFuture(Try<T>&& t) {
543 return Future<T>(new detail::Core<T>(std::move(t)));
547 Future<Unit> via(Executor* executor, int8_t priority) {
548 return makeFuture().via(executor, priority);
551 // mapSetCallback calls func(i, Try<T>) when every future completes
553 template <class T, class InputIterator, class F>
554 void mapSetCallback(InputIterator first, InputIterator last, F func) {
555 for (size_t i = 0; first != last; ++first, ++i) {
556 first->setCallback_([func, i](Try<T>&& t) {
557 func(i, std::move(t));
562 // collectAll (variadic)
564 template <typename... Fs>
565 typename detail::CollectAllVariadicContext<
566 typename std::decay<Fs>::type::value_type...>::type
567 collectAll(Fs&&... fs) {
568 auto ctx = std::make_shared<detail::CollectAllVariadicContext<
569 typename std::decay<Fs>::type::value_type...>>();
570 detail::collectVariadicHelper<detail::CollectAllVariadicContext>(
571 ctx, std::forward<typename std::decay<Fs>::type>(fs)...);
572 return ctx->p.getFuture();
575 // collectAll (iterator)
577 template <class InputIterator>
580 Try<typename std::iterator_traits<InputIterator>::value_type::value_type>>>
581 collectAll(InputIterator first, InputIterator last) {
583 typename std::iterator_traits<InputIterator>::value_type::value_type T;
585 struct CollectAllContext {
586 CollectAllContext(int n) : results(n) {}
587 ~CollectAllContext() {
588 p.setValue(std::move(results));
590 Promise<std::vector<Try<T>>> p;
591 std::vector<Try<T>> results;
594 auto ctx = std::make_shared<CollectAllContext>(std::distance(first, last));
595 mapSetCallback<T>(first, last, [ctx](size_t i, Try<T>&& t) {
596 ctx->results[i] = std::move(t);
598 return ctx->p.getFuture();
601 // collect (iterator)
605 template <typename T>
606 struct CollectContext {
608 explicit Nothing(int /* n */) {}
611 using Result = typename std::conditional<
612 std::is_void<T>::value,
614 std::vector<T>>::type;
616 using InternalResult = typename std::conditional<
617 std::is_void<T>::value,
619 std::vector<Optional<T>>>::type;
621 explicit CollectContext(int n) : result(n) {}
623 if (!threw.exchange(true)) {
624 // map Optional<T> -> T
625 std::vector<T> finalResult;
626 finalResult.reserve(result.size());
627 std::transform(result.begin(), result.end(),
628 std::back_inserter(finalResult),
629 [](Optional<T>& o) { return std::move(o.value()); });
630 p.setValue(std::move(finalResult));
633 inline void setPartialResult(size_t i, Try<T>& t) {
634 result[i] = std::move(t.value());
637 InternalResult result;
638 std::atomic<bool> threw {false};
643 template <class InputIterator>
644 Future<typename detail::CollectContext<
645 typename std::iterator_traits<InputIterator>::value_type::value_type>::Result>
646 collect(InputIterator first, InputIterator last) {
648 typename std::iterator_traits<InputIterator>::value_type::value_type T;
650 auto ctx = std::make_shared<detail::CollectContext<T>>(
651 std::distance(first, last));
652 mapSetCallback<T>(first, last, [ctx](size_t i, Try<T>&& t) {
653 if (t.hasException()) {
654 if (!ctx->threw.exchange(true)) {
655 ctx->p.setException(std::move(t.exception()));
657 } else if (!ctx->threw) {
658 ctx->setPartialResult(i, t);
661 return ctx->p.getFuture();
664 // collect (variadic)
666 template <typename... Fs>
667 typename detail::CollectVariadicContext<
668 typename std::decay<Fs>::type::value_type...>::type
669 collect(Fs&&... fs) {
670 auto ctx = std::make_shared<detail::CollectVariadicContext<
671 typename std::decay<Fs>::type::value_type...>>();
672 detail::collectVariadicHelper<detail::CollectVariadicContext>(
673 ctx, std::forward<typename std::decay<Fs>::type>(fs)...);
674 return ctx->p.getFuture();
677 // collectAny (iterator)
679 template <class InputIterator>
684 std::iterator_traits<InputIterator>::value_type::value_type>>>
685 collectAny(InputIterator first, InputIterator last) {
687 typename std::iterator_traits<InputIterator>::value_type::value_type T;
689 struct CollectAnyContext {
690 CollectAnyContext() {};
691 Promise<std::pair<size_t, Try<T>>> p;
692 std::atomic<bool> done {false};
695 auto ctx = std::make_shared<CollectAnyContext>();
696 mapSetCallback<T>(first, last, [ctx](size_t i, Try<T>&& t) {
697 if (!ctx->done.exchange(true)) {
698 ctx->p.setValue(std::make_pair(i, std::move(t)));
701 return ctx->p.getFuture();
704 // collectN (iterator)
706 template <class InputIterator>
707 Future<std::vector<std::pair<size_t, Try<typename
708 std::iterator_traits<InputIterator>::value_type::value_type>>>>
709 collectN(InputIterator first, InputIterator last, size_t n) {
711 std::iterator_traits<InputIterator>::value_type::value_type T;
712 typedef std::vector<std::pair<size_t, Try<T>>> V;
714 struct CollectNContext {
716 std::atomic<size_t> completed = {0};
719 auto ctx = std::make_shared<CollectNContext>();
721 if (size_t(std::distance(first, last)) < n) {
722 ctx->p.setException(std::runtime_error("Not enough futures"));
724 // for each completed Future, increase count and add to vector, until we
725 // have n completed futures at which point we fulfil our Promise with the
727 mapSetCallback<T>(first, last, [ctx, n](size_t i, Try<T>&& t) {
728 auto c = ++ctx->completed;
730 assert(ctx->v.size() < n);
731 ctx->v.emplace_back(i, std::move(t));
733 ctx->p.setTry(Try<V>(std::move(ctx->v)));
739 return ctx->p.getFuture();
744 template <class It, class T, class F>
745 Future<T> reduce(It first, It last, T&& initial, F&& func) {
747 return makeFuture(std::move(initial));
750 typedef typename std::iterator_traits<It>::value_type::value_type ItT;
751 typedef typename std::conditional<
752 detail::callableWith<F, T&&, Try<ItT>&&>::value, Try<ItT>, ItT>::type Arg;
753 typedef isTry<Arg> IsTry;
755 folly::MoveWrapper<T> minitial(std::move(initial));
756 auto sfunc = std::make_shared<F>(std::move(func));
758 auto f = first->then([minitial, sfunc](Try<ItT>& head) mutable {
759 return (*sfunc)(std::move(*minitial),
760 head.template get<IsTry::value, Arg&&>());
763 for (++first; first != last; ++first) {
764 f = collectAll(f, *first).then([sfunc](std::tuple<Try<T>, Try<ItT>>& t) {
765 return (*sfunc)(std::move(std::get<0>(t).value()),
766 // Either return a ItT&& or a Try<ItT>&& depending
767 // on the type of the argument of func.
768 std::get<1>(t).template get<IsTry::value, Arg&&>());
775 // window (collection)
777 template <class Collection, class F, class ItT, class Result>
778 std::vector<Future<Result>>
779 window(Collection input, F func, size_t n) {
780 struct WindowContext {
781 WindowContext(Collection&& i, F&& fn)
782 : input_(std::move(i)), promises_(input_.size()),
785 std::atomic<size_t> i_ {0};
787 std::vector<Promise<Result>> promises_;
790 static inline void spawn(const std::shared_ptr<WindowContext>& ctx) {
791 size_t i = ctx->i_++;
792 if (i < ctx->input_.size()) {
793 // Using setCallback_ directly since we don't need the Future
794 ctx->func_(std::move(ctx->input_[i])).setCallback_(
795 // ctx is captured by value
796 [ctx, i](Try<Result>&& t) {
797 ctx->promises_[i].setTry(std::move(t));
798 // Chain another future onto this one
799 spawn(std::move(ctx));
805 auto max = std::min(n, input.size());
807 auto ctx = std::make_shared<WindowContext>(
808 std::move(input), std::move(func));
810 for (size_t i = 0; i < max; ++i) {
811 // Start the first n Futures
812 WindowContext::spawn(ctx);
815 std::vector<Future<Result>> futures;
816 futures.reserve(ctx->promises_.size());
817 for (auto& promise : ctx->promises_) {
818 futures.emplace_back(promise.getFuture());
827 template <class I, class F>
828 Future<I> Future<T>::reduce(I&& initial, F&& func) {
829 folly::MoveWrapper<I> minitial(std::move(initial));
830 folly::MoveWrapper<F> mfunc(std::move(func));
831 return then([minitial, mfunc](T& vals) mutable {
832 auto ret = std::move(*minitial);
833 for (auto& val : vals) {
834 ret = (*mfunc)(std::move(ret), std::move(val));
840 // unorderedReduce (iterator)
842 template <class It, class T, class F, class ItT, class Arg>
843 Future<T> unorderedReduce(It first, It last, T initial, F func) {
845 return makeFuture(std::move(initial));
848 typedef isTry<Arg> IsTry;
850 struct UnorderedReduceContext {
851 UnorderedReduceContext(T&& memo, F&& fn, size_t n)
852 : lock_(), memo_(makeFuture<T>(std::move(memo))),
853 func_(std::move(fn)), numThens_(0), numFutures_(n), promise_()
855 folly::MicroSpinLock lock_; // protects memo_ and numThens_
858 size_t numThens_; // how many Futures completed and called .then()
859 size_t numFutures_; // how many Futures in total
863 auto ctx = std::make_shared<UnorderedReduceContext>(
864 std::move(initial), std::move(func), std::distance(first, last));
869 [ctx](size_t /* i */, Try<ItT>&& t) {
870 folly::MoveWrapper<Try<ItT>> mt(std::move(t));
871 // Futures can be completed in any order, simultaneously.
872 // To make this non-blocking, we create a new Future chain in
873 // the order of completion to reduce the values.
874 // The spinlock just protects chaining a new Future, not actually
875 // executing the reduce, which should be really fast.
876 folly::MSLGuard lock(ctx->lock_);
877 ctx->memo_ = ctx->memo_.then([ctx, mt](T&& v) mutable {
878 // Either return a ItT&& or a Try<ItT>&& depending
879 // on the type of the argument of func.
880 return ctx->func_(std::move(v),
881 mt->template get<IsTry::value, Arg&&>());
883 if (++ctx->numThens_ == ctx->numFutures_) {
884 // After reducing the value of the last Future, fulfill the Promise
885 ctx->memo_.setCallback_(
886 [ctx](Try<T>&& t2) { ctx->promise_.setValue(std::move(t2)); });
890 return ctx->promise_.getFuture();
896 Future<T> Future<T>::within(Duration dur, Timekeeper* tk) {
897 return within(dur, TimedOut(), tk);
902 Future<T> Future<T>::within(Duration dur, E e, Timekeeper* tk) {
905 Context(E ex) : exception(std::move(ex)), promise() {}
907 Future<Unit> thisFuture;
909 std::atomic<bool> token {false};
912 std::shared_ptr<Timekeeper> tks;
914 tks = folly::detail::getTimekeeperSingleton();
915 tk = DCHECK_NOTNULL(tks.get());
918 auto ctx = std::make_shared<Context>(std::move(e));
920 ctx->thisFuture = this->then([ctx](Try<T>&& t) mutable {
921 // TODO: "this" completed first, cancel "after"
922 if (ctx->token.exchange(true) == false) {
923 ctx->promise.setTry(std::move(t));
927 tk->after(dur).then([ctx](Try<Unit> const& t) mutable {
928 // "after" completed first, cancel "this"
929 ctx->thisFuture.raise(TimedOut());
930 if (ctx->token.exchange(true) == false) {
931 if (t.hasException()) {
932 ctx->promise.setException(std::move(t.exception()));
934 ctx->promise.setException(std::move(ctx->exception));
939 return ctx->promise.getFuture().via(getExecutor());
945 Future<T> Future<T>::delayed(Duration dur, Timekeeper* tk) {
946 return collectAll(*this, futures::sleep(dur, tk))
947 .then([](std::tuple<Try<T>, Try<Unit>> tup) {
948 Try<T>& t = std::get<0>(tup);
949 return makeFuture<T>(std::move(t));
956 void waitImpl(Future<T>& f) {
957 // short-circuit if there's nothing to do
958 if (f.isReady()) return;
960 FutureBatonType baton;
961 f.setCallback_([&](const Try<T>& /* t */) { baton.post(); });
967 void waitImpl(Future<T>& f, Duration dur) {
968 // short-circuit if there's nothing to do
969 if (f.isReady()) return;
971 folly::MoveWrapper<Promise<T>> promise;
972 auto ret = promise->getFuture();
973 auto baton = std::make_shared<FutureBatonType>();
974 f.setCallback_([baton, promise](Try<T>&& t) mutable {
975 promise->setTry(std::move(t));
979 if (baton->timed_wait(dur)) {
985 void waitViaImpl(Future<T>& f, DrivableExecutor* e) {
986 while (!f.isReady()) {
994 Future<T>& Future<T>::wait() & {
995 detail::waitImpl(*this);
1000 Future<T>&& Future<T>::wait() && {
1001 detail::waitImpl(*this);
1002 return std::move(*this);
1006 Future<T>& Future<T>::wait(Duration dur) & {
1007 detail::waitImpl(*this, dur);
1012 Future<T>&& Future<T>::wait(Duration dur) && {
1013 detail::waitImpl(*this, dur);
1014 return std::move(*this);
1018 Future<T>& Future<T>::waitVia(DrivableExecutor* e) & {
1019 detail::waitViaImpl(*this, e);
1024 Future<T>&& Future<T>::waitVia(DrivableExecutor* e) && {
1025 detail::waitViaImpl(*this, e);
1026 return std::move(*this);
1030 T Future<T>::get() {
1031 return std::move(wait().value());
1035 T Future<T>::get(Duration dur) {
1038 return std::move(value());
1045 T Future<T>::getVia(DrivableExecutor* e) {
1046 return std::move(waitVia(e).value());
1052 static bool equals(const Try<T>& t1, const Try<T>& t2) {
1053 return t1.value() == t2.value();
1059 Future<bool> Future<T>::willEqual(Future<T>& f) {
1060 return collectAll(*this, f).then([](const std::tuple<Try<T>, Try<T>>& t) {
1061 if (std::get<0>(t).hasValue() && std::get<1>(t).hasValue()) {
1062 return detail::TryEquals<T>::equals(std::get<0>(t), std::get<1>(t));
1071 Future<T> Future<T>::filter(F predicate) {
1072 auto p = folly::makeMoveWrapper(std::move(predicate));
1073 return this->then([p](T val) {
1074 T const& valConstRef = val;
1075 if (!(*p)(valConstRef)) {
1076 throw PredicateDoesNotObtain();
1083 template <class Callback>
1084 auto Future<T>::thenMulti(Callback&& fn)
1085 -> decltype(this->then(std::forward<Callback>(fn))) {
1086 // thenMulti with one callback is just a then
1087 return then(std::forward<Callback>(fn));
1091 template <class Callback, class... Callbacks>
1092 auto Future<T>::thenMulti(Callback&& fn, Callbacks&&... fns)
1093 -> decltype(this->then(std::forward<Callback>(fn)).
1094 thenMulti(std::forward<Callbacks>(fns)...)) {
1095 // thenMulti with two callbacks is just then(a).thenMulti(b, ...)
1096 return then(std::forward<Callback>(fn)).
1097 thenMulti(std::forward<Callbacks>(fns)...);
1101 template <class Callback, class... Callbacks>
1102 auto Future<T>::thenMultiWithExecutor(Executor* x, Callback&& fn,
1104 -> decltype(this->then(std::forward<Callback>(fn)).
1105 thenMulti(std::forward<Callbacks>(fns)...)) {
1106 // thenMultiExecutor with two callbacks is
1107 // via(x).then(a).thenMulti(b, ...).via(oldX)
1108 auto oldX = getExecutor();
1110 return then(std::forward<Callback>(fn)).
1111 thenMulti(std::forward<Callbacks>(fns)...).via(oldX);
1115 template <class Callback>
1116 auto Future<T>::thenMultiWithExecutor(Executor* x, Callback&& fn)
1117 -> decltype(this->then(std::forward<Callback>(fn))) {
1118 // thenMulti with one callback is just a then with an executor
1119 return then(x, std::forward<Callback>(fn));
1123 inline Future<Unit> when(bool p, F thunk) {
1124 return p ? thunk().unit() : makeFuture();
1127 template <class P, class F>
1128 Future<Unit> whileDo(P predicate, F thunk) {
1130 return thunk().then([=] {
1131 return whileDo(predicate, thunk);
1134 return makeFuture();
1138 Future<Unit> times(const int n, F thunk) {
1139 auto count = folly::makeMoveWrapper(
1140 std::unique_ptr<std::atomic<int>>(new std::atomic<int>(0))
1142 return folly::whileDo([=]() mutable {
1143 return (*count)->fetch_add(1) < n;
1148 template <class It, class F, class ItT, class Result>
1149 std::vector<Future<Result>> map(It first, It last, F func) {
1150 std::vector<Future<Result>> results;
1151 for (auto it = first; it != last; it++) {
1152 results.push_back(it->then(func));
1162 struct retrying_policy_raw_tag {};
1163 struct retrying_policy_fut_tag {};
1165 template <class Policy>
1166 struct retrying_policy_traits {
1167 using ew = exception_wrapper;
1168 FOLLY_CREATE_HAS_MEMBER_FN_TRAITS(has_op_call, operator());
1169 template <class Ret>
1170 using has_op = typename std::integral_constant<bool,
1171 has_op_call<Policy, Ret(size_t, const ew&)>::value ||
1172 has_op_call<Policy, Ret(size_t, const ew&) const>::value>;
1173 using is_raw = has_op<bool>;
1174 using is_fut = has_op<Future<bool>>;
1175 using tag = typename std::conditional<
1176 is_raw::value, retrying_policy_raw_tag, typename std::conditional<
1177 is_fut::value, retrying_policy_fut_tag, void>::type>::type;
1180 template <class Policy, class FF>
1181 typename std::result_of<FF(size_t)>::type
1182 retrying(size_t k, Policy&& p, FF&& ff) {
1183 using F = typename std::result_of<FF(size_t)>::type;
1184 using T = typename F::value_type;
1186 auto pm = makeMoveWrapper(p);
1187 auto ffm = makeMoveWrapper(ff);
1188 return f.onError([=](exception_wrapper x) mutable {
1189 auto q = (*pm)(k, x);
1190 auto xm = makeMoveWrapper(std::move(x));
1191 return q.then([=](bool r) mutable {
1193 ? retrying(k, pm.move(), ffm.move())
1194 : makeFuture<T>(xm.move());
1199 template <class Policy, class FF>
1200 typename std::result_of<FF(size_t)>::type
1201 retrying(Policy&& p, FF&& ff, retrying_policy_raw_tag) {
1202 auto pm = makeMoveWrapper(std::move(p));
1203 auto q = [=](size_t k, exception_wrapper x) {
1204 return makeFuture<bool>((*pm)(k, x));
1206 return retrying(0, std::move(q), std::forward<FF>(ff));
1209 template <class Policy, class FF>
1210 typename std::result_of<FF(size_t)>::type
1211 retrying(Policy&& p, FF&& ff, retrying_policy_fut_tag) {
1212 return retrying(0, std::forward<Policy>(p), std::forward<FF>(ff));
1215 // jittered exponential backoff, clamped to [backoff_min, backoff_max]
1216 template <class URNG>
1217 Duration retryingJitteredExponentialBackoffDur(
1219 Duration backoff_min,
1220 Duration backoff_max,
1221 double jitter_param,
1224 auto dist = std::normal_distribution<double>(0.0, jitter_param);
1225 auto jitter = std::exp(dist(rng));
1226 auto backoff = d(d::rep(jitter * backoff_min.count() * std::pow(2, n - 1)));
1227 return std::max(backoff_min, std::min(backoff_max, backoff));
1230 template <class Policy, class URNG>
1231 std::function<Future<bool>(size_t, const exception_wrapper&)>
1232 retryingPolicyCappedJitteredExponentialBackoff(
1234 Duration backoff_min,
1235 Duration backoff_max,
1236 double jitter_param,
1239 auto pm = makeMoveWrapper(std::move(p));
1240 auto rngp = std::make_shared<URNG>(std::move(rng));
1241 return [=](size_t n, const exception_wrapper& ex) mutable {
1242 if (n == max_tries) { return makeFuture(false); }
1243 return (*pm)(n, ex).then([=](bool v) {
1244 if (!v) { return makeFuture(false); }
1245 auto backoff = detail::retryingJitteredExponentialBackoffDur(
1246 n, backoff_min, backoff_max, jitter_param, *rngp);
1247 return futures::sleep(backoff).then([] { return true; });
1252 template <class Policy, class URNG>
1253 std::function<Future<bool>(size_t, const exception_wrapper&)>
1254 retryingPolicyCappedJitteredExponentialBackoff(
1256 Duration backoff_min,
1257 Duration backoff_max,
1258 double jitter_param,
1261 retrying_policy_raw_tag) {
1262 auto pm = makeMoveWrapper(std::move(p));
1263 auto q = [=](size_t n, const exception_wrapper& e) {
1264 return makeFuture((*pm)(n, e));
1266 return retryingPolicyCappedJitteredExponentialBackoff(
1275 template <class Policy, class URNG>
1276 std::function<Future<bool>(size_t, const exception_wrapper&)>
1277 retryingPolicyCappedJitteredExponentialBackoff(
1279 Duration backoff_min,
1280 Duration backoff_max,
1281 double jitter_param,
1284 retrying_policy_fut_tag) {
1285 return retryingPolicyCappedJitteredExponentialBackoff(
1296 template <class Policy, class FF>
1297 typename std::result_of<FF(size_t)>::type
1298 retrying(Policy&& p, FF&& ff) {
1299 using tag = typename detail::retrying_policy_traits<Policy>::tag;
1300 return detail::retrying(std::forward<Policy>(p), std::forward<FF>(ff), tag());
1304 std::function<bool(size_t, const exception_wrapper&)>
1305 retryingPolicyBasic(
1307 return [=](size_t n, const exception_wrapper&) { return n < max_tries; };
1310 template <class Policy, class URNG>
1311 std::function<Future<bool>(size_t, const exception_wrapper&)>
1312 retryingPolicyCappedJitteredExponentialBackoff(
1314 Duration backoff_min,
1315 Duration backoff_max,
1316 double jitter_param,
1319 using tag = typename detail::retrying_policy_traits<Policy>::tag;
1320 return detail::retryingPolicyCappedJitteredExponentialBackoff(
1331 std::function<Future<bool>(size_t, const exception_wrapper&)>
1332 retryingPolicyCappedJitteredExponentialBackoff(
1334 Duration backoff_min,
1335 Duration backoff_max,
1336 double jitter_param) {
1337 auto p = [](size_t, const exception_wrapper&) { return true; };
1338 return retryingPolicyCappedJitteredExponentialBackoff(
1349 // Instantiate the most common Future types to save compile time
1350 extern template class Future<Unit>;
1351 extern template class Future<bool>;
1352 extern template class Future<int>;
1353 extern template class Future<int64_t>;
1354 extern template class Future<std::string>;
1355 extern template class Future<double>;
1357 } // namespace folly