+++ /dev/null
-/* Copyright (c) 2016-2020. The SimGrid Team.
- * All rights reserved. */
-
-/* This program is free software; you can redistribute it and/or modify it
- * under the terms of the license (GNU LGPL) which comes with this package. */
-
-#ifndef SIMGRID_KERNEL_FUTURE_HPP
-#define SIMGRID_KERNEL_FUTURE_HPP
-
-#include <functional>
-#include <future>
-#include <memory>
-#include <utility>
-#include <type_traits>
-
-#include <boost/optional.hpp>
-
-#include <xbt/base.h>
-#include <xbt/functional.hpp>
-#include <xbt/future.hpp>
-
-namespace simgrid {
-namespace kernel {
-
-// There are the public classes:
-template<class T> class Future;
-template<class T> class Promise;
-
-// Those are implementation details:
-enum class FutureStatus;
-template<class T> class FutureState;
-
-enum class FutureStatus {
- not_ready,
- ready,
- done,
-};
-
-template<class T>
-struct is_future : std::false_type {};
-template<class T>
-struct is_future<Future<T>> : std::true_type {};
-
-/** Bases stuff for all @ref simgrid::kernel::FutureState<T> */
-class FutureStateBase {
-public:
- // No copy/move:
- FutureStateBase(FutureStateBase const&) = delete;
- FutureStateBase& operator=(FutureStateBase const&) = delete;
-
- XBT_PUBLIC void schedule(simgrid::xbt::Task<void()>&& job) const;
-
- void set_exception(std::exception_ptr exception)
- {
- xbt_assert(exception_ == nullptr);
- if (status_ != FutureStatus::not_ready)
- throw std::future_error(std::future_errc::promise_already_satisfied);
- exception_ = std::move(exception);
- this->set_ready();
- }
-
- void set_continuation(simgrid::xbt::Task<void()>&& continuation)
- {
- xbt_assert(not continuation_);
- switch (status_) {
- case FutureStatus::done:
- // This is not supposed to happen if continuation is set
- // via the Promise:
- xbt_die("Set continuation on finished future");
- break;
- case FutureStatus::ready:
- // The future is ready, execute the continuation directly.
- // We might execute it from the event loop instead:
- schedule(std::move(continuation));
- break;
- case FutureStatus::not_ready:
- // The future is not ready so we must keep the continuation for
- // executing it later:
- continuation_ = std::move(continuation);
- break;
- default:
- DIE_IMPOSSIBLE;
- }
- }
-
- FutureStatus get_status() const
- {
- return status_;
- }
-
- bool is_ready() const
- {
- return status_ == FutureStatus::ready;
- }
-
-protected:
- FutureStateBase() = default;
- ~FutureStateBase() = default;
-
- /** Set the future as ready and trigger the continuation */
- void set_ready()
- {
- status_ = FutureStatus::ready;
- if (continuation_) {
- // We unregister the continuation before executing it.
- // We need to do this because the current implementation of the
- // continuation has a shared_ptr to the FutureState.
- auto continuation = std::move(continuation_);
- this->schedule(std::move(continuation));
- }
- }
-
- /** Set the future as done and raise an exception if any
- *
- * This does half the job of `.get()`.
- **/
- void resolve()
- {
- if (status_ != FutureStatus::ready)
- xbt_die("Deadlock: this future is not ready");
- status_ = FutureStatus::done;
- if (exception_) {
- std::exception_ptr exception = std::move(exception_);
- exception_ = nullptr;
- std::rethrow_exception(std::move(exception));
- }
- }
-
-private:
- FutureStatus status_ = FutureStatus::not_ready;
- std::exception_ptr exception_;
- simgrid::xbt::Task<void()> continuation_;
-};
-
-/** Shared state for future and promises
- *
- * You are not expected to use them directly but to create them
- * implicitly through a @ref simgrid::kernel::Promise.
- * Alternatively kernel operations could inherit or contain FutureState
- * if they are managed with std::shared_ptr.
- **/
-template<class T>
-class FutureState : public FutureStateBase {
-public:
- void set_value(T value)
- {
- if (this->get_status() != FutureStatus::not_ready)
- throw std::future_error(std::future_errc::promise_already_satisfied);
- value_ = std::move(value);
- this->set_ready();
- }
-
- T get()
- {
- this->resolve();
- xbt_assert(this->value_);
- auto result = std::move(this->value_.get());
- this->value_ = boost::optional<T>();
- return result;
- }
-
-private:
- boost::optional<T> value_;
-};
-
-template<class T>
-class FutureState<T&> : public FutureStateBase {
-public:
- void set_value(T& value)
- {
- if (this->get_status() != FutureStatus::not_ready)
- throw std::future_error(std::future_errc::promise_already_satisfied);
- value_ = &value;
- this->set_ready();
- }
-
- T& get()
- {
- this->resolve();
- xbt_assert(this->value_);
- T* result = value_;
- value_ = nullptr;
- return *result;
- }
-
-private:
- T* value_ = nullptr;
-};
-
-template<>
-class FutureState<void> : public FutureStateBase {
-public:
- void set_value()
- {
- if (this->get_status() != FutureStatus::not_ready)
- throw std::future_error(std::future_errc::promise_already_satisfied);
- this->set_ready();
- }
-
- void get()
- {
- this->resolve();
- }
-};
-
-template <class T> void bind_promise(Promise<T>&& promise, Future<T> future)
-{
- class PromiseBinder {
- public:
- explicit PromiseBinder(Promise<T>&& promise) : promise_(std::move(promise)) {}
- void operator()(Future<T> future) { simgrid::xbt::set_promise(promise_, future); }
-
- private:
- Promise<T> promise_;
- };
- future.then_(PromiseBinder(std::move(promise)));
-}
-
-template <class T> Future<T> unwrap_future(Future<Future<T>> future);
-
-/** Result of some (probably) asynchronous operation in the SimGrid kernel
- *
- * @ref simgrid::simix::Future and @ref simgrid::simix::Future provide an
- * abstraction for asynchronous stuff happening in the SimGrid kernel. They
- * are based on C++1z futures.
- *
- * The future represents a value which will be available at some point when this
- * asynchronous operation is finished. Alternatively, if this operations fails,
- * the result of the operation might be an exception.
- *
- * As the operation is possibly no terminated yet, we cannot get the result
- * yet. Moreover, as we cannot block in the SimGrid kernel we cannot wait for
- * it. However, we can attach some code/callback/continuation which will be
- * executed when the operation terminates.
- *
- * Example of the API (`simgrid::kernel::createProcess` does not exist):
- * <pre>
- * // Create a new process using the Worker code, this process returns
- * // a std::string:
- * simgrid::kernel::Future<std::string> future =
- * simgrid::kernel::createProcess("worker42", host, Worker(42));
- * // At this point, we just created the process so the result is not available.
- * // However, we can attach some work do be done with this result:
- * future.then([](simgrid::kernel::Future<std::string> result) {
- * // This code is called when the operation is completed so the result is
- * // available:
- * try {
- * // Try to get value, this might throw an exception if the operation
- * // failed (such as an exception thrown by the worker process):
- * std::string value = result.get();
- * XBT_INFO("Value: %s", value.c_str());
- * }
- * catch(std::exception& e) {
- * // This is an exception from the asynchronous operation:
- * XBT_INFO("Error: %e", e.what());
- * }
- * );
- * </pre>
- *
- * This is based on C++1z std::future but with some differences:
- *
- * * there is no thread synchronization (atomic, mutex, condition variable,
- * etc.) because everything happens in the SimGrid event loop;
- *
- * * it is purely asynchronous, you are expected to use `.then()`;
- *
- * * inside the `.then()`, `.get()` can be used;
- *
- * * `.get()` can only be used when `.is_ready()` (as everything happens in
- * a single-thread, the future would be guaranteed to deadlock if `.get()`
- * is called when the future is not ready);
- *
- * * there is no future chaining support for now (`.then().then()`);
- *
- * * there is no sharing (`shared_future`) for now.
- */
-template<class T>
-class Future {
-public:
- Future() = default;
- explicit Future(std::shared_ptr<FutureState<T>> state) : state_(std::move(state)) {}
- ~Future() = default;
-
- // Move type:
- Future(Future&) = delete;
- Future& operator=(const Future&) = delete;
- Future(Future&&) noexcept = default;
- Future& operator=(Future&&) noexcept = default;
-
- /** Whether the future is valid:.
- *
- * A future which as been used (`.then` of `.get`) becomes invalid.
- *
- * We can use `.then` on a valid future.
- */
- bool valid() const
- {
- return state_ != nullptr;
- }
-
- /** Whether the future is ready
- *
- * A future is ready when it has an associated value or exception.
- *
- * We can use `.get()` on ready futures.
- **/
- bool is_ready() const
- {
- return state_ != nullptr && state_->is_ready();
- }
-
- /** Attach a continuation to this future
- *
- * This is like .then() but avoid the creation of a new future.
- */
- template<class F>
- void then_(F continuation)
- {
- if (state_ == nullptr)
- throw std::future_error(std::future_errc::no_state);
- // Give shared-ownership to the continuation:
- auto state = std::move(state_);
- state->set_continuation(simgrid::xbt::make_task(std::move(continuation), state));
- }
-
- /** Attach a continuation to this future
- *
- * This version never does future unwrapping.
- */
- template <class F> auto then_no_unwrap(F continuation) -> Future<decltype(continuation(std::move(*this)))>
- {
- typedef decltype(continuation(std::move(*this))) R;
- if (state_ == nullptr)
- throw std::future_error(std::future_errc::no_state);
- auto state = std::move(state_);
- // Create a new future...
- Promise<R> promise;
- Future<R> future = promise.get_future();
- // ...and when the current future is ready...
- state->set_continuation(simgrid::xbt::make_task(
- [](Promise<R> promise, std::shared_ptr<FutureState<T>> state, F continuation) {
- // ...set the new future value by running the continuation.
- Future<T> future(std::move(state));
- simgrid::xbt::fulfill_promise(promise, [&continuation, &future] { return continuation(std::move(future)); });
- },
- std::move(promise), state, std::move(continuation)));
- return future;
- }
-
- /** Attach a continuation to this future
- *
- * The future must be valid in order to make this call.
- * The continuation is executed when the future becomes ready.
- * The future becomes invalid after this call.
- *
- * @param continuation This function is called with a ready future
- * the future is ready
- * @exception std::future_error no state is associated with the future
- */
- template <class F>
- auto then(F continuation) -> typename std::enable_if<not is_future<decltype(continuation(std::move(*this)))>::value,
- Future<decltype(continuation(std::move(*this)))>>::type
- {
- return this->then_no_unwrap(std::move(continuation));
- }
-
- /** Attach a continuation to this future (future chaining) */
- template<class F>
- auto then(F continuation)
- -> typename std::enable_if<
- is_future<decltype(continuation(std::move(*this)))>::value,
- decltype(continuation(std::move(*this)))
- >::type
- {
- return unwrap_future(this->then_no_unwrap(std::move(continuation)));
- }
-
- /** Get the value from the future
- *
- * The future must be valid and ready in order to make this call.
- * std::future blocks when the future is not ready but we are
- * completely single-threaded so blocking would be a deadlock.
- * After the call, the future becomes invalid.
- *
- * @return value of the future
- * @exception any Exception from the future
- * @exception std::future_error no state is associated with the future
- */
- T get()
- {
- if (state_ == nullptr)
- throw std::future_error(std::future_errc::no_state);
- std::shared_ptr<FutureState<T>> state = std::move(state_);
- return state->get();
- }
-
-private:
- std::shared_ptr<FutureState<T>> state_;
-};
-
-template <class T> Future<T> unwrap_future(Future<Future<T>> future)
-{
- Promise<T> promise;
- Future<T> result = promise.get_future();
- bind_promise(std::move(promise), std::move(future));
- return result;
-}
-
-/** Producer side of a @ref simgrid::kernel::Future
- *
- * A @ref Promise is connected to some `Future` and can be used to
- * set its result.
- *
- * Similar to std::promise
- *
- * <code>
- * // Create a promise and a future:
- * auto promise = std::make_shared<simgrid::kernel::Promise<T>>();
- * auto future = promise->get_future();
- *
- * simgrid::simix::Timer::set(date, [promise] {
- * try {
- * int value = compute_the_value();
- * if (value < 0)
- * throw std::logic_error("Bad value");
- * // Whenever the operation is completed, we set the value
- * // for the future:
- * promise.set_value(value);
- * }
- * catch (...) {
- * // If an error occurred, we can set an exception which
- * // will be thrown by future.get():
- * promise.set_exception(std::current_exception());
- * }
- * });
- *
- * // Return the future to the caller:
- * return future;
- * </code>
- **/
-template<class T>
-class Promise {
-public:
- Promise() = default;
- explicit Promise(std::shared_ptr<FutureState<T>> state) : state_(std::move(state)) {}
-
- // Move type
- Promise(Promise const&) = delete;
- Promise& operator=(Promise const&) = delete;
- Promise(Promise&& that) noexcept : state_(std::move(that.state_)) { std::swap(future_get_, that.future_get_); }
-
- Promise& operator=(Promise&& that) noexcept
- {
- this->state_ = std::move(that.state_);
- this->future_get_ = that.future_get_;
- that.future_get_ = false;
- return *this;
- }
- Future<T> get_future()
- {
- if (state_ == nullptr)
- throw std::future_error(std::future_errc::no_state);
- if (future_get_)
- throw std::future_error(std::future_errc::future_already_retrieved);
- future_get_ = true;
- return Future<T>(state_);
- }
- void set_value(T value)
- {
- if (state_ == nullptr)
- throw std::future_error(std::future_errc::no_state);
- state_->set_value(std::move(value));
- }
- void set_exception(std::exception_ptr exception)
- {
- if (state_ == nullptr)
- throw std::future_error(std::future_errc::no_state);
- state_->set_exception(std::move(exception));
- }
- ~Promise()
- {
- if (state_ && state_->get_status() == FutureStatus::not_ready)
- state_->set_exception(std::make_exception_ptr(
- std::future_error(std::future_errc::broken_promise)));
- }
-
-private:
- std::shared_ptr<FutureState<T>> state_{new FutureState<T>()};
- bool future_get_ = false;
-};
-
-template<>
-class Promise<void> {
-public:
- Promise() = default;
- explicit Promise(std::shared_ptr<FutureState<void>> state) : state_(std::move(state)) {}
- ~Promise()
- {
- if (state_ && state_->get_status() == FutureStatus::not_ready)
- state_->set_exception(std::make_exception_ptr(
- std::future_error(std::future_errc::broken_promise)));
- }
-
- // Move type
- Promise(Promise const&) = delete;
- Promise& operator=(Promise const&) = delete;
- Promise(Promise&& that) noexcept : state_(std::move(that.state_)) { std::swap(future_get_, that.future_get_); }
- Promise& operator=(Promise&& that) noexcept
- {
- this->state_ = std::move(that.state_);
- this->future_get_ = that.future_get_;
- that.future_get_ = false;
- return *this;
- }
-
- Future<void> get_future()
- {
- if (state_ == nullptr)
- throw std::future_error(std::future_errc::no_state);
- if (future_get_)
- throw std::future_error(std::future_errc::future_already_retrieved);
- future_get_ = true;
- return Future<void>(state_);
- }
- void set_value() const
- {
- if (state_ == nullptr)
- throw std::future_error(std::future_errc::no_state);
- state_->set_value();
- }
- void set_exception(std::exception_ptr exception) const
- {
- if (state_ == nullptr)
- throw std::future_error(std::future_errc::no_state);
- state_->set_exception(std::move(exception));
- }
-
-private:
- std::shared_ptr<FutureState<void>> state_{new FutureState<void>()};
- bool future_get_ = false;
-};
-
-}
-}
-
-#endif
