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// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
// vim: ts=8 sw=2 smarttab
/*
* Ceph - scalable distributed file system
*
* Copyright (C) 2004-2006 Sage Weil <sage@newdream.net>
*
* This is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License version 2.1, as published by the Free Software
* Foundation. See file COPYING.
*
*/
#ifndef CEPH_COMMON_WAITER_H
#define CEPH_COMMON_WAITER_H
#include <condition_variable>
#include <tuple>
#include <boost/asio/async_result.hpp>
#include "include/ceph_assert.h"
#include "include/function2.hpp"
#include "common/ceph_mutex.h"
namespace ceph::async {
namespace detail {
// For safety reasons (avoiding undefined behavior around sequence
// points) std::reference_wrapper disallows move construction. This
// harms us in cases where we want to pass a reference in to something
// that unavoidably moves.
//
// It should not be used generally.
template<typename T>
class rvalue_reference_wrapper {
public:
// types
using type = T;
rvalue_reference_wrapper(T& r) noexcept
: p(std::addressof(r)) {}
// We write our semantics to match those of reference collapsing. If
// we're treated as an lvalue, collapse to one.
rvalue_reference_wrapper(const rvalue_reference_wrapper&) noexcept = default;
rvalue_reference_wrapper(rvalue_reference_wrapper&&) noexcept = default;
// assignment
rvalue_reference_wrapper& operator=(
const rvalue_reference_wrapper& x) noexcept = default;
rvalue_reference_wrapper& operator=(
rvalue_reference_wrapper&& x) noexcept = default;
operator T& () const noexcept {
return *p;
}
T& get() const noexcept {
return *p;
}
operator T&& () noexcept {
return std::move(*p);
}
T&& get() noexcept {
return std::move(*p);
}
template<typename... Args>
std::result_of_t<T&(Args&&...)> operator ()(Args&&... args ) const {
return (*p)(std::forward<Args>(args)...);
}
template<typename... Args>
std::result_of_t<T&&(Args&&...)> operator ()(Args&&... args ) {
return std::move(*p)(std::forward<Args>(args)...);
}
private:
T* p;
};
class base {
protected:
ceph::mutex lock = ceph::make_mutex("ceph::async::detail::base::lock");
ceph::condition_variable cond;
bool has_value = false;
~base() = default;
auto wait_base() {
std::unique_lock l(lock);
cond.wait(l, [this](){ return has_value; });
return l;
}
auto exec_base() {
std::unique_lock l(lock);
// There's no really good way to handle being called twice
// without being reset.
ceph_assert(!has_value);
has_value = true;
cond.notify_one();
return l;
}
};
}
// waiter is a replacement for C_SafeCond and friends. It is the
// moral equivalent of a future but plays well with a world of
// callbacks.
template<typename ...S>
class waiter;
template<>
class waiter<> final : public detail::base {
public:
void wait() {
wait_base();
has_value = false;
}
void operator()() {
exec_base();
}
auto ref() {
return detail::rvalue_reference_wrapper(*this);
}
operator fu2::unique_function<void() &&>() {
return fu2::unique_function<void() &&>(ref());
}
};
template<typename Ret>
class waiter<Ret> final : public detail::base {
std::aligned_storage_t<sizeof(Ret)> ret;
public:
Ret wait() {
auto l = wait_base();
auto r = reinterpret_cast<Ret*>(&ret);
auto t = std::move(*r);
r->~Ret();
has_value = false;
return t;
}
void operator()(Ret&& _ret) {
auto l = exec_base();
auto r = reinterpret_cast<Ret*>(&ret);
*r = std::move(_ret);
}
void operator()(const Ret& _ret) {
auto l = exec_base();
auto r = reinterpret_cast<Ret*>(&ret);
*r = std::move(_ret);
}
auto ref() {
return detail::rvalue_reference_wrapper(*this);
}
operator fu2::unique_function<void(Ret) &&>() {
return fu2::unique_function<void(Ret) &&>(ref());
}
~waiter() {
if (has_value)
reinterpret_cast<Ret*>(&ret)->~Ret();
}
};
template<typename ...Ret>
class waiter final : public detail::base {
std::tuple<Ret...> ret;
public:
std::tuple<Ret...> wait() {
using std::tuple;
auto l = wait_base();
return std::move(ret);
auto r = reinterpret_cast<std::tuple<Ret...>*>(&ret);
auto t = std::move(*r);
r->~tuple<Ret...>();
has_value = false;
return t;
}
void operator()(Ret&&... _ret) {
auto l = exec_base();
auto r = reinterpret_cast<std::tuple<Ret...>*>(&ret);
*r = std::forward_as_tuple(_ret...);
}
void operator()(const Ret&... _ret) {
auto l = exec_base();
auto r = reinterpret_cast<std::tuple<Ret...>*>(&ret);
*r = std::forward_as_tuple(_ret...);
}
auto ref() {
return detail::rvalue_reference_wrapper(*this);
}
operator fu2::unique_function<void(Ret...) &&>() {
return fu2::unique_function<void(Ret...) &&>(ref());
}
~waiter() {
using std::tuple;
if (has_value)
reinterpret_cast<tuple<Ret...>*>(&ret)->~tuple<Ret...>();
}
};
}
#endif // CEPH_COMMON_WAITER_H
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