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Future.h
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Future.h
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#pragma once
#include "Executor.h"
#include "Promise.h"
#include "Task.h"
#include "StackAllocator.h"
/*
* Future object attached to a running coroutine. Implement await_* APIs.
*/
template <typename T>
class Future {
public:
Future(const Future&) = delete;
Future(Future&& other) : promise_(other.promise_) {
other.promise_ = nullptr;
}
void wait() {
prep(*this).get();
}
T& get() {
assert(promise_->state_ == Promise<T>::State::HAS_RESULT);
assert(promise_->state_ == Promise<T>::State::HAS_RESULT);
if (promise_->resultValue_) {
return *promise_->resultValue_;
}
std::rethrow_exception(promise_->resultException_);
}
T& operator*() {
return get();
}
T* operator->() {
return &get();
}
bool await_ready() {
return promise_->state_.load(std::memory_order_acquire) == Promise<T>::State::HAS_RESULT;
}
bool await_suspend(std::experimental::coroutine_handle<> awaiter) {
auto state = promise_->state_.load(std::memory_order_acquire);
if (state == Promise<T>::State::HAS_RESULT) {
return false;
}
assert(state == Promise<T>::State::EMPTY);
promise_->awaiter_ = std::move(awaiter);
if (promise_->state_.compare_exchange_strong(
state,
Promise<T>::State::HAS_AWAITER,
std::memory_order_release,
std::memory_order_acquire)) {
return true;
}
assert(promise_->state_ == Promise<T>::State::HAS_RESULT);
return false;
}
T await_resume() { return std::move(get()); }
~Future() {
if (!promise_) {
return;
}
auto state = promise_->state_.load(std::memory_order_acquire);
do {
assert(state != Promise<T>::State::DETACHED);
assert(state != Promise<T>::State::HAS_AWAITER);
if (state == Promise<T>::State::HAS_RESULT) {
auto ch = std::experimental::coroutine_handle<Promise<T>>::from_promise(*promise_);
assert(ch.done());
ch.destroy();
return;
}
assert(state == Promise<T>::State::EMPTY);
} while (!promise_->state_.compare_exchange_weak(
state,
Promise<T>::State::DETACHED,
std::memory_order::memory_order_release,
std::memory_order::memory_order_acquire));
}
private:
friend class Task<T>;
std::future<void> prep(Future& future) {
co_await future;
co_return;
};
Future(Promise<T>& promise) : promise_(&promise) {
}
Promise<T>* promise_;
};
/*
* Start coroutine on a given executor, using fixed size stack allocator.
*/
template <typename F, typename... Args>
auto spawnWithStack(Executor& executor, size_t stackSize, F&& f, Args&&... args) {
ExecutionContext ec;
ec.executor = &executor;
ec.allocator = StackAllocator::create(stackSize);
auto task = f(ec.allocator, std::forward<Args>(args)...);
auto future = std::move(task).start(ec);
return future;
}
/*
* Start coroutine on a given executor. Malloc allocator is used.
*/
template <typename F, typename... Args>
auto spawn(Executor& executor, F&& f, Args&&... args) {
ExecutionContext ec;
ec.executor = &executor;
auto task = f(nullptr, std::forward<Args>(args)...);
auto future = std::move(task).start(ec);
return future;
}
/*
* Schedule coroutine to be started inline using current executor and allocator.
* The coroutine doesn't start until the return object of call(...) is awaited on.
*/
template <typename F, typename... Args>
auto call(F&& f, Args&&... args) {
return CallableTask<F, Args...>(std::forward<F>(f), std::forward<Args>(args)...);
}