2 * Copyright 2014 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.
23 #include <type_traits>
26 #include <folly/MoveWrapper.h>
27 #include <folly/futures/Deprecated.h>
28 #include <folly/futures/DrivableExecutor.h>
29 #include <folly/futures/Promise.h>
30 #include <folly/futures/Try.h>
31 #include <folly/futures/FutureException.h>
32 #include <folly/futures/detail/Types.h>
36 template <class> struct Promise;
39 struct isFuture : std::false_type {
44 struct isFuture<Future<T>> : std::true_type {
49 struct isTry : std::false_type {};
52 struct isTry<Try<T>> : std::true_type {};
56 template <class> struct Core;
57 template <class...> struct VariadicContext;
59 template<typename F, typename... Args>
60 using resultOf = decltype(std::declval<F>()(std::declval<Args>()...));
62 template <typename...>
65 template <typename Arg, typename... Args>
66 struct ArgType<Arg, Args...> {
72 typedef void FirstArg;
75 template <bool isTry, typename F, typename... Args>
77 typedef resultOf<F, Args...> Result;
80 template<typename F, typename... Args>
83 typename = detail::resultOf<T, Args...>>
84 static constexpr std::true_type
85 check(std::nullptr_t) { return std::true_type{}; };
88 static constexpr std::false_type
89 check(...) { return std::false_type{}; };
91 typedef decltype(check<F>(nullptr)) type;
92 static constexpr bool value = type::value;
95 template<typename T, typename F>
96 struct callableResult {
97 typedef typename std::conditional<
98 callableWith<F>::value,
99 detail::argResult<false, F>,
100 typename std::conditional<
101 callableWith<F, Try<T>&&>::value,
102 detail::argResult<true, F, Try<T>&&>,
103 typename std::conditional<
104 callableWith<F, Try<T>&>::value,
105 detail::argResult<true, F, Try<T>&>,
106 typename std::conditional<
107 callableWith<F, T&&>::value,
108 detail::argResult<false, F, T&&>,
109 detail::argResult<false, F, T&>>::type>::type>::type>::type Arg;
110 typedef isFuture<typename Arg::Result> ReturnsFuture;
111 typedef Future<typename ReturnsFuture::Inner> Return;
115 struct callableResult<void, F> {
116 typedef typename std::conditional<
117 callableWith<F>::value,
118 detail::argResult<false, F>,
119 typename std::conditional<
120 callableWith<F, Try<void>&&>::value,
121 detail::argResult<true, F, Try<void>&&>,
122 detail::argResult<true, F, Try<void>&>>::type>::type Arg;
123 typedef isFuture<typename Arg::Result> ReturnsFuture;
124 typedef Future<typename ReturnsFuture::Inner> Return;
127 template <typename L>
128 struct Extract : Extract<decltype(&L::operator())> { };
130 template <typename Class, typename R, typename... Args>
131 struct Extract<R(Class::*)(Args...) const> {
132 typedef isFuture<R> ReturnsFuture;
133 typedef Future<typename ReturnsFuture::Inner> Return;
134 typedef typename ReturnsFuture::Inner RawReturn;
135 typedef typename ArgType<Args...>::FirstArg FirstArg;
138 template <typename Class, typename R, typename... Args>
139 struct Extract<R(Class::*)(Args...)> {
140 typedef isFuture<R> ReturnsFuture;
141 typedef Future<typename ReturnsFuture::Inner> Return;
142 typedef typename ReturnsFuture::Inner RawReturn;
143 typedef typename ArgType<Args...>::FirstArg FirstArg;
150 /// This namespace is for utility functions that would usually be static
151 /// members of Future, except they don't make sense there because they don't
152 /// depend on the template type (rather, on the type of their arguments in
153 /// some cases). This is the least-bad naming scheme we could think of. Some
154 /// of the functions herein have really-likely-to-collide names, like "map"
157 /// Returns a Future that will complete after the specified duration. The
158 /// Duration typedef of a `std::chrono` duration type indicates the
159 /// resolution you can expect to be meaningful (milliseconds at the time of
160 /// writing). Normally you wouldn't need to specify a Timekeeper, we will
161 /// use the global futures timekeeper (we run a thread whose job it is to
162 /// keep time for futures timeouts) but we provide the option for power
165 /// The Timekeeper thread will be lazily created the first time it is
166 /// needed. If your program never uses any timeouts or other time-based
167 /// Futures you will pay no Timekeeper thread overhead.
168 Future<void> sleep(Duration, Timekeeper* = nullptr);
174 typedef T value_type;
177 Future(Future const&) = delete;
178 Future& operator=(Future const&) = delete;
181 Future(Future&&) noexcept;
182 Future& operator=(Future&&);
185 template <class F = T>
187 Future(const typename std::enable_if<!std::is_void<F>::value, F>::type& val);
189 template <class F = T>
191 Future(typename std::enable_if<!std::is_void<F>::value, F>::type&& val);
193 template <class F = T,
194 typename std::enable_if<std::is_void<F>::value, int>::type = 0>
199 /** Return the reference to result. Should not be called if !isReady().
200 Will rethrow the exception if an exception has been
203 typename std::add_lvalue_reference<T>::type
205 typename std::add_lvalue_reference<const T>::type
208 /// Returns an inactive Future which will call back on the other side of
209 /// executor (when it is activated).
211 /// NB remember that Futures activate when they destruct. This is good,
212 /// it means that this will work:
214 /// f.via(e).then(a).then(b);
216 /// a and b will execute in the same context (the far side of e), because
217 /// the Future (temporary variable) created by via(e) does not call back
218 /// until it destructs, which is after then(a) and then(b) have been wired
221 /// But this is still racy:
223 /// f = f.via(e).then(a);
225 // The ref-qualifier allows for `this` to be moved out so we
226 // don't get access-after-free situations in chaining.
227 // https://akrzemi1.wordpress.com/2014/06/02/ref-qualifiers/
228 template <typename Executor>
229 Future<T> via(Executor* executor) &&;
231 /// This variant creates a new future, where the ref-qualifier && version
232 /// moves `this` out. This one is less efficient but avoids confusing users
233 /// when "return f.via(x);" fails.
234 template <typename Executor>
235 Future<T> via(Executor* executor) &;
237 /** True when the result (or exception) is ready. */
238 bool isReady() const;
240 /** A reference to the Try of the value */
243 /// Block until the future is fulfilled. Returns the value (moved out), or
244 /// throws the exception. The future must not already have a callback.
247 /// Block until the future is fulfilled, or until timed out. Returns the
248 /// value (moved out), or throws the exception (which might be a TimedOut
252 /// Call e->drive() repeatedly until the future is fulfilled. Examples
253 /// of DrivableExecutor include EventBase and ManualExecutor. Returns the
254 /// value (moved out), or throws the exception.
255 T getVia(DrivableExecutor* e);
257 /** When this Future has completed, execute func which is a function that
267 Func shall return either another Future or a value.
269 A Future for the return type of func is returned.
271 Future<string> f2 = f1.then([](Try<T>&&) { return string("foo"); });
273 The Future given to the functor is ready, and the functor may call
274 value(), which may rethrow if this has captured an exception. If func
275 throws, the exception will be captured in the Future that is returned.
277 /* TODO n3428 and other async frameworks have something like then(scheduler,
278 Future), we might want to support a similar API which could be
279 implemented a little more efficiently than
280 f.via(executor).then(callback) */
281 template <typename F, typename R = detail::callableResult<T, F>>
282 typename R::Return then(F func) {
283 typedef typename R::Arg Arguments;
284 return thenImplementation<F, R>(std::move(func), Arguments());
287 /// Variant where func is an member function
290 /// R doWork(Try<T>&&); }
293 /// Future<R> f2 = f1.then(w, &Worker::doWork);
294 template <typename Caller, typename R, typename... Args>
295 Future<typename isFuture<R>::Inner>
296 then(Caller *instance, R(Caller::*func)(Args...));
298 /// Convenience method for ignoring the value and creating a Future<void>.
299 /// Exceptions still propagate.
302 /// Set an error callback for this Future. The callback should take a single
303 /// argument of the type that you want to catch, and should return a value of
304 /// the same type as this Future, or a Future of that type (see overload
305 /// below). For instance,
309 /// throw std::runtime_error("oh no!");
312 /// .onError([] (std::runtime_error& e) {
313 /// LOG(INFO) << "std::runtime_error: " << e.what();
314 /// return -1; // or makeFuture<int>(-1)
317 typename std::enable_if<
318 !detail::Extract<F>::ReturnsFuture::value,
322 /// Overload of onError where the error callback returns a Future<T>
324 typename std::enable_if<
325 detail::Extract<F>::ReturnsFuture::value,
329 /// Like onError, but for timeouts. example:
331 /// Future<int> f = makeFuture<int>(42)
332 /// .delayed(long_time)
333 /// .onTimeout(short_time,
334 /// []() -> int{ return -1; });
338 /// Future<int> f = makeFuture<int>(42)
339 /// .delayed(long_time)
340 /// .onTimeout(short_time,
341 /// []() { return makeFuture<int>(some_exception); });
343 Future<T> onTimeout(Duration, F&& func, Timekeeper* = nullptr);
345 /// This is not the method you're looking for.
347 /// This needs to be public because it's used by make* and when*, and it's
348 /// not worth listing all those and their fancy template signatures as
349 /// friends. But it's not for public consumption.
351 void setCallback_(F&& func);
353 /// A Future's callback is executed when all three of these conditions have
354 /// become true: it has a value (set by the Promise), it has a callback (set
355 /// by then), and it is active (active by default).
357 /// Inactive Futures will activate upon destruction.
358 Future<T>& activate() & {
362 Future<T>& deactivate() & {
366 Future<T> activate() && {
368 return std::move(*this);
370 Future<T> deactivate() && {
372 return std::move(*this);
376 return core_->isActive();
380 void raise(E&& exception) {
381 raise(make_exception_wrapper<typename std::remove_reference<E>::type>(
382 std::move(exception)));
385 /// Raise an interrupt. If the promise holder has an interrupt
386 /// handler it will be called and potentially stop asynchronous work from
387 /// being done. This is advisory only - a promise holder may not set an
388 /// interrupt handler, or may do anything including ignore. But, if you know
389 /// your future supports this the most likely result is stopping or
390 /// preventing the asynchronous operation (if in time), and the promise
391 /// holder setting an exception on the future. (That may happen
392 /// asynchronously, of course.)
393 void raise(exception_wrapper interrupt);
396 raise(FutureCancellation());
399 /// Throw TimedOut if this Future does not complete within the given
400 /// duration from now. The optional Timeekeeper is as with futures::sleep().
401 Future<T> within(Duration, Timekeeper* = nullptr);
403 /// Throw the given exception if this Future does not complete within the
404 /// given duration from now. The optional Timeekeeper is as with
405 /// futures::sleep().
407 Future<T> within(Duration, E exception, Timekeeper* = nullptr);
409 /// Delay the completion of this Future for at least this duration from
410 /// now. The optional Timekeeper is as with futures::sleep().
411 Future<T> delayed(Duration, Timekeeper* = nullptr);
413 /// Block until this Future is complete. Returns a reference to this Future.
416 /// Overload of wait() for rvalue Futures
417 Future<T>&& wait() &&;
419 /// Block until this Future is complete or until the given Duration passes.
420 /// Returns a reference to this Future
421 Future<T>& wait(Duration) &;
423 /// Overload of wait(Duration) for rvalue Futures
424 Future<T>&& wait(Duration) &&;
426 /// Call e->drive() repeatedly until the future is fulfilled. Examples
427 /// of DrivableExecutor include EventBase and ManualExecutor. Returns a
428 /// reference to this Future so that you can chain calls if desired.
429 /// value (moved out), or throws the exception.
430 Future<T>& waitVia(DrivableExecutor* e) &;
432 /// Overload of waitVia() for rvalue Futures
433 Future<T>&& waitVia(DrivableExecutor* e) &&;
436 typedef detail::Core<T>* corePtr;
438 // shared core state object
442 Future(corePtr obj) : core_(obj) {}
446 void throwIfInvalid() const;
448 friend class Promise<T>;
450 // Variant: returns a value
451 // e.g. f.then([](Try<T> t){ return t.value(); });
452 template <typename F, typename R, bool isTry, typename... Args>
453 typename std::enable_if<!R::ReturnsFuture::value, typename R::Return>::type
454 thenImplementation(F func, detail::argResult<isTry, F, Args...>);
456 // Variant: returns a Future
457 // e.g. f.then([](Try<T> t){ return makeFuture<T>(t); });
458 template <typename F, typename R, bool isTry, typename... Args>
459 typename std::enable_if<R::ReturnsFuture::value, typename R::Return>::type
460 thenImplementation(F func, detail::argResult<isTry, F, Args...>);
464 Make a completed Future by moving in a value. e.g.
467 auto f = makeFuture(std::move(foo));
471 auto f = makeFuture<string>("foo");
474 Future<typename std::decay<T>::type> makeFuture(T&& t);
476 /** Make a completed void Future. */
477 Future<void> makeFuture();
479 /** Make a completed Future by executing a function. If the function throws
480 we capture the exception, otherwise we capture the result. */
484 typename std::enable_if<
485 !std::is_reference<F>::value, bool>::type sdf = false)
486 -> Future<decltype(func())>;
491 -> Future<decltype(func())>;
493 /// Make a failed Future from an exception_ptr.
494 /// Because the Future's type cannot be inferred you have to specify it, e.g.
496 /// auto f = makeFuture<string>(std::current_exception());
498 Future<T> makeFuture(std::exception_ptr const& e) DEPRECATED;
500 /// Make a failed Future from an exception_wrapper.
502 Future<T> makeFuture(exception_wrapper ew);
504 /** Make a Future from an exception type E that can be passed to
505 std::make_exception_ptr(). */
506 template <class T, class E>
507 typename std::enable_if<std::is_base_of<std::exception, E>::value,
509 makeFuture(E const& e);
511 /** Make a Future out of a Try */
513 Future<T> makeFuture(Try<T>&& t);
516 * Return a new Future that will call back on the given Executor.
517 * This is just syntactic sugar for makeFuture().via(executor)
519 * @param executor the Executor to call back on
521 * @returns a void Future that will call back on the given executor
523 template <typename Executor>
524 Future<void> via(Executor* executor);
526 /** When all the input Futures complete, the returned Future will complete.
527 Errors do not cause early termination; this Future will always succeed
528 after all its Futures have finished (whether successfully or with an
531 The Futures are moved in, so your copies are invalid. If you need to
532 chain further from these Futures, use the variant with an output iterator.
534 This function is thread-safe for Futures running on different threads. But
535 if you are doing anything non-trivial after, you will probably want to
536 follow with `via(executor)` because it will complete in whichever thread the
537 last Future completes in.
539 The return type for Future<T> input is a Future<std::vector<Try<T>>>
541 template <class InputIterator>
542 Future<std::vector<Try<
543 typename std::iterator_traits<InputIterator>::value_type::value_type>>>
544 whenAll(InputIterator first, InputIterator last);
546 /// This version takes a varying number of Futures instead of an iterator.
547 /// The return type for (Future<T1>, Future<T2>, ...) input
548 /// is a Future<std::tuple<Try<T1>, Try<T2>, ...>>.
549 /// The Futures are moved in, so your copies are invalid.
550 template <typename... Fs>
551 typename detail::VariadicContext<
552 typename std::decay<Fs>::type::value_type...>::type
555 /** The result is a pair of the index of the first Future to complete and
556 the Try. If multiple Futures complete at the same time (or are already
557 complete when passed in), the "winner" is chosen non-deterministically.
559 This function is thread-safe for Futures running on different threads.
561 template <class InputIterator>
564 Try<typename std::iterator_traits<InputIterator>::value_type::value_type>>>
565 whenAny(InputIterator first, InputIterator last);
567 /** when n Futures have completed, the Future completes with a vector of
568 the index and Try of those n Futures (the indices refer to the original
569 order, but the result vector will be in an arbitrary order)
573 template <class InputIterator>
574 Future<std::vector<std::pair<
576 Try<typename std::iterator_traits<InputIterator>::value_type::value_type>>>>
577 whenN(InputIterator first, InputIterator last, size_t n);
581 #include <folly/futures/Future-inl.h>