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#pragma once
#include "task_result.h"
#include <util/system/yassert.h>
#include <coroutine>
namespace NActors {
template<class T>
class TTask;
/**
* This exception is commonly thrown when task is cancelled
*/
class TTaskCancelled : public std::exception {
public:
const char* what() const noexcept {
return "Task cancelled";
}
};
namespace NDetail {
template<class T>
class TTaskPromise;
template<class T>
using TTaskHandle = std::coroutine_handle<TTaskPromise<T>>;
template<class T>
class TTaskAwaiter {
public:
explicit TTaskAwaiter(TTaskHandle<T> handle)
: Handle(handle)
{
Y_VERIFY_DEBUG(Handle);
}
TTaskAwaiter(TTaskAwaiter&& rhs)
: Handle(std::exchange(rhs.Handle, {}))
{}
TTaskAwaiter& operator=(const TTaskAwaiter&) = delete;
TTaskAwaiter& operator=(TTaskAwaiter&&) = delete;
~TTaskAwaiter() noexcept {
if (Handle) {
Handle.destroy();
}
}
// We can only await a task that has not started yet
static bool await_ready() noexcept { return false; }
// Some arbitrary continuation c suspended and awaits the task
TTaskHandle<T> await_suspend(std::coroutine_handle<> c) noexcept {
Y_VERIFY_DEBUG(Handle);
Handle.promise().SetContinuation(c);
return Handle;
}
TTaskResult<T>&& await_resume() noexcept {
Y_VERIFY_DEBUG(Handle);
return std::move(Handle.promise().Result);
}
private:
TTaskHandle<T> Handle;
};
template<class T>
class TTaskResultAwaiter final : public TTaskAwaiter<T> {
public:
using TTaskAwaiter<T>::TTaskAwaiter;
T&& await_resume() {
return TTaskAwaiter<T>::await_resume().Value();
}
};
template<>
class TTaskResultAwaiter<void> final : public TTaskAwaiter<void> {
public:
using TTaskAwaiter<void>::TTaskAwaiter;
void await_resume() {
TTaskAwaiter<void>::await_resume().Value();
}
};
template<class T>
class TTaskResultHandlerBase {
public:
void unhandled_exception() noexcept {
Result.SetException(std::current_exception());
}
protected:
TTaskResult<T> Result;
};
template<class T>
class TTaskResultHandler : public TTaskResultHandlerBase<T> {
public:
template<class TResult>
void return_value(TResult&& value) {
this->Result.SetValue(std::forward<TResult>(value));
}
};
template<>
class TTaskResultHandler<void> : public TTaskResultHandlerBase<void> {
public:
void return_void() noexcept {
this->Result.SetValue();
}
};
template<class T>
class TTaskPromise final
: public TTaskResultHandler<T>
{
friend class TTaskAwaiter<T>;
public:
TTask<T> get_return_object() noexcept;
static auto initial_suspend() noexcept { return std::suspend_always{}; }
struct TFinalSuspend {
static bool await_ready() noexcept { return false; }
static void await_resume() noexcept { Y_FAIL("unexpected coroutine resume"); }
static std::coroutine_handle<> await_suspend(std::coroutine_handle<TTaskPromise<T>> h) noexcept {
auto next = std::exchange(h.promise().Continuation, std::noop_coroutine());
Y_VERIFY_DEBUG(next, "Task finished without a continuation");
return next;
}
};
static auto final_suspend() noexcept { return TFinalSuspend{}; }
private:
void SetContinuation(std::coroutine_handle<> continuation) noexcept {
Y_VERIFY_DEBUG(!Continuation, "Task can only be awaited once");
Continuation = continuation;
}
private:
std::coroutine_handle<> Continuation;
};
} // namespace NDetail
/**
* Represents a task that has not been started yet
*/
template<class T>
class TTask final {
public:
using promise_type = NDetail::TTaskPromise<T>;
using value_type = T;
public:
TTask() noexcept = default;
explicit TTask(NDetail::TTaskHandle<T> handle) noexcept
: Handle(handle)
{}
TTask(TTask&& rhs) noexcept
: Handle(std::exchange(rhs.Handle, {}))
{}
~TTask() {
if (Handle) {
Handle.destroy();
}
}
TTask& operator=(TTask&& rhs) noexcept {
if (Y_LIKELY(this != &rhs)) {
auto handle = std::exchange(Handle, {});
Handle = std::exchange(rhs.Handle, {});
if (handle) {
handle.destroy();
}
}
return *this;
}
/**
* Returns true for a valid task object
*/
explicit operator bool() const noexcept {
return bool(Handle);
}
/**
* Starts task and returns TTaskResult<T> when it completes
*/
auto WhenDone() && noexcept {
Y_VERIFY_DEBUG(Handle, "Cannot await an empty task");
return NDetail::TTaskAwaiter<T>(std::exchange(Handle, {}));
}
/**
* Starts task and returns its result when it completes
*/
auto operator co_await() && noexcept {
Y_VERIFY_DEBUG(Handle, "Cannot await an empty task");
return NDetail::TTaskResultAwaiter<T>(std::exchange(Handle, {}));
}
private:
NDetail::TTaskHandle<T> Handle;
};
namespace NDetail {
template<class T>
inline TTask<T> TTaskPromise<T>::get_return_object() noexcept {
return TTask<T>(TTaskHandle<T>::from_promise(*this));
}
} // namespace NDetail
} // namespace NActors
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