Epoll.hpp

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// The Reactive C++ Toolbox.
// Copyright (C) 2013-2019 Swirly Cloud Limited
// Copyright (C) 2022 Reactive Markets Limited
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
 
#ifndef TOOLBOX_IO_EPOLL_HPP
#define TOOLBOX_IO_EPOLL_HPP
 
#include <toolbox/io/Event.hpp>
#include <toolbox/io/TimerFd.hpp>
 
#include <sys/epoll.h>
 
namespace toolbox {
namespace os {
 
inline FileHandle epoll_create(int size, std::error_code& ec) noexcept
{
    const auto ret = ::epoll_create(size);
    if (ret < 0) {
        ec = make_error(errno);
    }
    return ret;
}
 
inline FileHandle epoll_create(int size)
{
    const auto fd = ::epoll_create(size);
    if (fd < 0) {
        throw std::system_error{make_error(errno), "epoll_create"};
    }
    return fd;
}
 
inline FileHandle epoll_create1(int flags, std::error_code& ec) noexcept
{
    const auto ret = ::epoll_create1(flags);
    if (ret < 0) {
        ec = make_error(errno);
    }
    return ret;
}
 
inline FileHandle epoll_create1(int flags)
{
    const auto fd = ::epoll_create1(flags);
    if (fd < 0) {
        throw std::system_error{make_error(errno), "epoll_create1"};
    }
    return fd;
}
 
inline int epoll_ctl(int epfd, int op, int fd, epoll_event event, std::error_code& ec) noexcept
{
    const auto ret = ::epoll_ctl(epfd, op, fd, &event);
    if (ret < 0) {
        ec = make_error(errno);
    }
    return ret;
}
 
inline void epoll_ctl(int epfd, int op, int fd, epoll_event event)
{
    const auto ret = ::epoll_ctl(epfd, op, fd, &event);
    if (ret < 0) {
        throw std::system_error{make_error(errno), "epoll_ctl"};
    }
}
 
inline int epoll_wait(int epfd, epoll_event* events, int maxevents, int timeout,
                      std::error_code& ec) noexcept
{
    const auto ret = ::epoll_wait(epfd, events, maxevents, timeout);
    if (ret < 0) {
        ec = make_error(errno);
    }
    return ret;
}
 
inline int epoll_wait(int epfd, epoll_event* events, int maxevents, int timeout)
{
    const auto ret = ::epoll_wait(epfd, events, maxevents, timeout);
    if (ret < 0) {
        throw std::system_error{make_error(errno), "epoll_wait"};
    }
    return ret;
}
 
} // namespace os
inline namespace io {
 
enum : unsigned {
    EpollIn = EPOLLIN,
 
    EpollOut = EPOLLOUT,
 
    EpollRdHup = EPOLLRDHUP,
 
    EpollPri = EPOLLPRI,
 
    EpollErr = EPOLLERR,
 
    EpollHup = EPOLLHUP,
 
    EpollEt = EPOLLET,
 
    EpollOneShot = EPOLLONESHOT,
};
 
using EpollEvent = epoll_event;
 
class Epoll {
  public:
    using Event = EpollEvent;
 
    static constexpr int fd(const Event& ev) noexcept
    {
        return static_cast<int>(ev.data.u64 & 0xffffffff);
    }
    static constexpr int sid(const Event& ev) noexcept
    {
        return static_cast<int>(ev.data.u64 >> 32);
    }
    explicit Epoll(int flags = 0)
    : epfd_{os::epoll_create1(flags)}
    , tfd_{TFD_NONBLOCK}
    {
        add(tfd_.fd(), 0, EpollIn);
    }
    ~Epoll() { del(tfd_.fd()); }
 
    // Copy.
    Epoll(const Epoll&) = delete;
    Epoll& operator=(const Epoll&) = delete;
 
    // Move.
    Epoll(Epoll&&) noexcept = default;
    Epoll& operator=(Epoll&&) noexcept = default;
 
    int timer_fd() const noexcept { return tfd_.fd(); }
 
    void swap(Epoll& rhs) noexcept { std::swap(epfd_, rhs.epfd_); }
 
    int wait(Event buf[], std::size_t size, std::error_code& ec) noexcept
    {
        MonoTime timeout{};
        // Only set the timer if it has changed.
        if (timeout != timeout_) {
            // A zero timeout will disarm the timer.
            tfd_.set_time(0, timeout, ec);
            if (ec) {
                return 0;
            }
            timeout_ = timeout;
        }
        return os::epoll_wait(*epfd_, buf, size, -1, ec);
    }
    int wait(Event buf[], std::size_t size, MonoTime timeout, std::error_code& ec) noexcept
    {
        // Only set the timer if it has changed.
        if (timeout != timeout_) {
            // A zero timeout will disarm the timer.
            tfd_.set_time(0, timeout, ec);
            if (ec) {
                return 0;
            }
            timeout_ = timeout;
        }
        // Do not block if timer is zero.
        return os::epoll_wait(*epfd_, buf, size, is_zero(timeout) ? 0 : -1, ec);
    }
    void add(int fd, int sid, unsigned events)
    {
        Event ev;
        mod(ev, fd, sid, events);
        os::epoll_ctl(*epfd_, EPOLL_CTL_ADD, fd, ev);
    }
    void del(int fd) noexcept
    {
        // In kernel versions before 2.6.9, the EPOLL_CTL_DEL operation required a non-null pointer
        // in event, even though this argument is ignored.
        Event ev{};
        std::error_code ec;
        os::epoll_ctl(*epfd_, EPOLL_CTL_DEL, fd, ev, ec);
    }
    void mod(int fd, int sid, unsigned events, std::error_code& ec) noexcept
    {
        Event ev;
        mod(ev, fd, sid, events);
        os::epoll_ctl(*epfd_, EPOLL_CTL_MOD, fd, ev, ec);
    }
    void mod(int fd, int sid, unsigned events)
    {
        Event ev;
        mod(ev, fd, sid, events);
        os::epoll_ctl(*epfd_, EPOLL_CTL_MOD, fd, ev);
    }
 
  private:
    static void mod(Event& ev, int fd, int sid, unsigned events) noexcept
    {
        ev.events = events;
        ev.data.u64 = static_cast<std::uint64_t>(sid) << 32 | fd;
    }
    FileHandle epfd_;
    TimerFd<MonoClock> tfd_;
    MonoTime timeout_{};
};
 
} // namespace io
} // namespace toolbox
 
#endif // TOOLBOX_IO_EPOLL_HPP