unison/src/core/model/unix-fd-reader.cc

/*
 * Copyright (c) 2010 The Boeing Company
 *
 * SPDX-License-Identifier: GPL-2.0-only
 *
 * Author: Tom Goff <thomas.goff@boeing.com>
 */

#include "fatal-error.h"
#include "fd-reader.h"
#include "log.h"
#include "simple-ref-count.h"
#include "simulator.h"

#include <cerrno>
#include <cstring>
#include <fcntl.h>
#include <sys/select.h>
#include <thread>
#include <unistd.h> // close()

/**
 * @file
 * @ingroup system
 * ns3::FdReader implementation.
 */

namespace ns3
{

NS_LOG_COMPONENT_DEFINE("FdReader");

FdReader::FdReader()
    : m_fd(-1),
      m_stop(false),
      m_destroyEvent()
{
    NS_LOG_FUNCTION(this);
    m_evpipe[0] = -1;
    m_evpipe[1] = -1;
}

FdReader::~FdReader()
{
    NS_LOG_FUNCTION(this);
    Stop();
}

void
FdReader::Start(int fd, Callback<void, uint8_t*, ssize_t> readCallback)
{
    NS_LOG_FUNCTION(this << fd << &readCallback);
    int tmp;

    NS_ASSERT_MSG(!m_readThread.joinable(), "read thread already exists");

    // create a pipe for inter-thread event notification
    tmp = pipe(m_evpipe);
    if (tmp == -1)
    {
        NS_FATAL_ERROR("pipe() failed: " << std::strerror(errno));
    }

    // make the read end non-blocking
    tmp = fcntl(m_evpipe[0], F_GETFL);
    if (tmp == -1)
    {
        NS_FATAL_ERROR("fcntl() failed: " << std::strerror(errno));
    }
    if (fcntl(m_evpipe[0], F_SETFL, tmp | O_NONBLOCK) == -1)
    {
        NS_FATAL_ERROR("fcntl() failed: " << std::strerror(errno));
    }

    m_fd = fd;
    m_readCallback = readCallback;

    //
    // We're going to spin up a thread soon, so we need to make sure we have
    // a way to tear down that thread when the simulation stops.  Do this by
    // scheduling a "destroy time" method to make sure the thread exits before
    // proceeding.
    //
    if (!m_destroyEvent.IsPending())
    {
        // hold a reference to ensure that this object is not
        // deallocated before the destroy-time event fires
        this->Ref();
        m_destroyEvent = Simulator::ScheduleDestroy(&FdReader::DestroyEvent, this);
    }

    //
    // Now spin up a thread to read from the fd
    //
    NS_LOG_LOGIC("Spinning up read thread");

    m_readThread = std::thread(&FdReader::Run, this);
}

void
FdReader::DestroyEvent()
{
    NS_LOG_FUNCTION(this);
    Stop();
    this->Unref();
}

void
FdReader::Stop()
{
    NS_LOG_FUNCTION(this);
    m_stop = true;

    // signal the read thread
    if (m_evpipe[1] != -1)
    {
        char zero = 0;
        ssize_t len = write(m_evpipe[1], &zero, sizeof(zero));
        if (len != sizeof(zero))
        {
            NS_LOG_WARN("incomplete write(): " << std::strerror(errno));
        }
    }

    // join the read thread
    if (m_readThread.joinable())
    {
        m_readThread.join();
    }

    // close the write end of the event pipe
    if (m_evpipe[1] != -1)
    {
        close(m_evpipe[1]);
        m_evpipe[1] = -1;
    }

    // close the read end of the event pipe
    if (m_evpipe[0] != -1)
    {
        close(m_evpipe[0]);
        m_evpipe[0] = -1;
    }

    // reset everything else
    m_fd = -1;
    m_readCallback.Nullify();
    m_stop = false;
}

// This runs in a separate thread
void
FdReader::Run()
{
    NS_LOG_FUNCTION(this);
    int nfds;
    fd_set rfds;

    nfds = (m_fd > m_evpipe[0] ? m_fd : m_evpipe[0]) + 1;

    FD_ZERO(&rfds);
    FD_SET(m_fd, &rfds);
    FD_SET(m_evpipe[0], &rfds);

    for (;;)
    {
        int r;
        fd_set readfds = rfds;

        r = select(nfds, &readfds, nullptr, nullptr, nullptr);
        if (r == -1 && errno != EINTR)
        {
            NS_FATAL_ERROR("select() failed: " << std::strerror(errno));
        }

        if (FD_ISSET(m_evpipe[0], &readfds))
        {
            // drain the event pipe
            for (;;)
            {
                char buf[1024];
                ssize_t len = read(m_evpipe[0], buf, sizeof(buf));
                if (len == 0)
                {
                    NS_FATAL_ERROR("event pipe closed");
                }
                if (len < 0)
                {
                    if (errno == EAGAIN || errno == EINTR || errno == EWOULDBLOCK)
                    {
                        break;
                    }
                    else
                    {
                        NS_FATAL_ERROR("read() failed: " << std::strerror(errno));
                    }
                }
            }
        }

        if (m_stop)
        {
            // this thread is done
            break;
        }

        if (FD_ISSET(m_fd, &readfds))
        {
            FdReader::Data data = DoRead();
            // reading stops when m_len is zero
            if (data.m_len == 0)
            {
                break;
            }
            // the callback is only called when m_len is positive (data
            // is ignored if m_len is negative)
            else if (data.m_len > 0)
            {
                m_readCallback(data.m_buf, data.m_len);
            }
        }
    }
}

} // namespace ns3