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//
 
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// Copyright (c) 2026 Steve Gerbino
 
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//
 
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// Distributed under the Boost Software License, Version 1.0. (See accompanying
 
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// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
 
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//
 
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// Official repository: https://github.com/cppalliance/corosio
 
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//
 
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#ifndef BOOST_COROSIO_NATIVE_DETAIL_EPOLL_EPOLL_OP_HPP
 
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#define BOOST_COROSIO_NATIVE_DETAIL_EPOLL_EPOLL_OP_HPP
 
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#include <boost/corosio/detail/platform.hpp>
 
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#if BOOST_COROSIO_HAS_EPOLL
 
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#include <boost/corosio/native/detail/reactor/reactor_op.hpp>
 
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#include <boost/corosio/native/detail/reactor/reactor_descriptor_state.hpp>
 
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/*
 
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    epoll Operation State
 
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    =====================
 
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    Each async I/O operation has a corresponding epoll_op-derived struct that
 
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    holds the operation's state while it's in flight. The socket impl owns
 
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    fixed slots for each operation type (conn_, rd_, wr_), so only one
 
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    operation of each type can be pending per socket at a time.
 
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    Persistent Registration
 
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    -----------------------
 
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    File descriptors are registered with epoll once (via descriptor_state) and
 
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    stay registered until closed. The descriptor_state tracks which operations
 
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    are pending (read_op, write_op, connect_op). When an event arrives, the
 
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    reactor dispatches to the appropriate pending operation.
 
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    Impl Lifetime Management
 
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    ------------------------
 
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    When cancel() posts an op to the scheduler's ready queue, the socket impl
 
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    might be destroyed before the scheduler processes the op. The `impl_ptr`
 
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    member holds a shared_ptr to the impl, keeping it alive until the op
 
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    completes. This is set by cancel() and cleared in operator() after the
 
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    coroutine is resumed.
 
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    EOF Detection
 
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    -------------
 
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    For reads, 0 bytes with no error means EOF. But an empty user buffer also
 
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    returns 0 bytes. The `empty_buffer_read` flag distinguishes these cases.
 
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    SIGPIPE Prevention
 
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    ------------------
 
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    Writes use sendmsg() with MSG_NOSIGNAL instead of writev() to prevent
 
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    SIGPIPE when the peer has closed.
 
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*/
 
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namespace boost::corosio::detail {
 
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// Forward declarations
 
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class epoll_tcp_socket;
 
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class epoll_tcp_acceptor;
 
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struct epoll_op;
 
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// Forward declaration
 
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class epoll_scheduler;
 
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/// Per-descriptor state for persistent epoll registration.
 
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struct descriptor_state final : reactor_descriptor_state
 
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{};
 
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/// epoll base operation — thin wrapper over reactor_op.
 
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struct epoll_op : reactor_op<epoll_tcp_socket, epoll_tcp_acceptor>
 
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{
 
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    void operator()() override;
 
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};
 
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/// epoll connect operation.
 
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struct epoll_connect_op final : reactor_connect_op<epoll_op>
 
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{
 
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    void operator()() override;
 
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    void cancel() noexcept override;
 
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};
 
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/// epoll scatter-read operation.
 
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struct epoll_read_op final : reactor_read_op<epoll_op>
 
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{
 
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    void cancel() noexcept override;
 
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};
 
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/** Provides sendmsg(MSG_NOSIGNAL) with EINTR retry for epoll writes. */
 
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struct epoll_write_policy
 
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{
 
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    static ssize_t write(int fd, iovec* iovecs, int count) noexcept
 
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    {
 
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        msghdr msg{};
 
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        msg.msg_iov    = iovecs;
 
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        msg.msg_iovlen = static_cast<std::size_t>(count);
 
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        ssize_t n;
 
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        do
 
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        {
 
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            n = ::sendmsg(fd, &msg, MSG_NOSIGNAL);
 
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        }
 
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        while (n < 0 && errno == EINTR);
 
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        return n;
 
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    }
 
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};
 
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/// epoll gather-write operation.
 
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struct epoll_write_op final : reactor_write_op<epoll_op, epoll_write_policy>
 
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{
 
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    void cancel() noexcept override;
 
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};
 
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/** Provides accept4(SOCK_NONBLOCK|SOCK_CLOEXEC) with EINTR retry. */
 
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struct epoll_accept_policy
 
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{
 
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    static int do_accept(
 
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        int fd, sockaddr_storage& peer, socklen_t& addrlen_out) noexcept
 
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    {
 
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        addrlen_out = sizeof(peer);
 
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        int new_fd;
 
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        do
 
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        {
 
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            new_fd = ::accept4(
 
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                fd, reinterpret_cast<sockaddr*>(&peer), &addrlen_out,
 
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                SOCK_NONBLOCK | SOCK_CLOEXEC);
 
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        }
 
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        while (new_fd < 0 && errno == EINTR);
 
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        return new_fd;
 
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    }
 
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};
 
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/// epoll accept operation.
 
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struct epoll_accept_op final : reactor_accept_op<epoll_op, epoll_accept_policy>
 
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{
 
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    void operator()() override;
 
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    void cancel() noexcept override;
 
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};
 
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} // namespace boost::corosio::detail
 
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#endif // BOOST_COROSIO_HAS_EPOLL
 
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#endif // BOOST_COROSIO_NATIVE_DETAIL_EPOLL_EPOLL_OP_HPP