deskflow/src/lib/platform/XWindowsEventQueueBuffer.cpp

/*
 * Deskflow -- mouse and keyboard sharing utility
 * SPDX-FileCopyrightText: (C) 2012 - 2016 Symless Ltd.
 * SPDX-FileCopyrightText: (C) 2004 Chris Schoeneman
 * SPDX-License-Identifier: GPL-2.0-only WITH LicenseRef-OpenSSL-Exception
 */

#include "platform/XWindowsEventQueueBuffer.h"

#include "base/Event.h"
#include "base/IEventQueue.h"
#include "mt/Thread.h"

#include <fcntl.h>
#include <poll.h>
#include <unistd.h>

//
// EventQueueTimer
//

class EventQueueTimer
{
};

//
// XWindowsEventQueueBuffer
//

XWindowsEventQueueBuffer::XWindowsEventQueueBuffer(Display *display, Window window, IEventQueue *events)
    : m_events(events),
      m_display(display),
      m_window(window)
{
  assert(m_display != nullptr);
  assert(m_window != None);

  m_userEvent = XInternAtom(m_display, "DESKFLOW_USER_EVENT", False);
  // set up for pipe hack
  int result = pipe2(m_pipefd, O_NONBLOCK);
  assert(result == 0);
}

XWindowsEventQueueBuffer::~XWindowsEventQueueBuffer()
{
  // release pipe hack resources
  close(m_pipefd[0]);
  close(m_pipefd[1]);
}

int XWindowsEventQueueBuffer::getPendingCountLocked()
{
  std::scoped_lock lock{m_mutex};
  return XPending(m_display);
}

void XWindowsEventQueueBuffer::waitForEvent(double dtimeout)
{
  Thread::testCancel();

  // clear out the pipe in preparation for waiting.

  char buf[16];

  // with linux automake, warnings are treated as errors by default
  if (ssize_t read_response = read(m_pipefd[0], buf, 15); read_response < 0) {
    // todo: handle read response
  }

  {
    std::scoped_lock lock{m_mutex};
    // we're now waiting for events
    m_waiting = true;

    // push out pending events
    flush();
  }
  // calling flush may have queued up a new event.
  if (!XWindowsEventQueueBuffer::isEmpty()) {
    Thread::testCancel();
    return;
  }

  // use poll() to wait for a message from the X server or for timeout.
  // this is a good deal more efficient than polling and sleeping.
  struct pollfd pfds[2];
  pfds[0].fd = ConnectionNumber(m_display);
  pfds[0].events = POLLIN;
  pfds[1].fd = m_pipefd[0];
  pfds[1].events = POLLIN;
  int timeout = (dtimeout < 0.0) ? -1 : static_cast<int>(1000.0 * dtimeout);
  int remaining = timeout;
  int retval = 0;

  // It's possible that the X server has queued events locally
  // in xlib's event buffer and not pushed on to the fd. Hence we
  // can't simply monitor the fd as we may never be woken up.
  // ie addEvent calls flush, XFlush may not send via the fd hence
  // there is an event waiting to be sent but we must exit the poll
  // before it can.
  // Instead we poll for a brief period of time (so if events
  // queued locally in the xlib buffer can be processed)
  // and continue doing this until timeout is reached.
  // The human eye can notice 60hz (ansi) which is 16ms, however
  // we want to give the cpu a chance s owe up this to 25ms
#define TIMEOUT_DELAY 25

  while (((dtimeout < 0.0) || (remaining > 0)) && getPendingCountLocked() == 0 && retval == 0) {

    retval = poll(pfds, 2, TIMEOUT_DELAY); // 16ms = 60hz, but we make it > to
                                           // play nicely with the cpu
    if (pfds[1].revents & POLLIN) {
      ssize_t read_response = read(m_pipefd[0], buf, 15);

      // with linux automake, warnings are treated as errors by default
      if (read_response < 0) {
        // todo: handle read response
      }
    }
    remaining -= TIMEOUT_DELAY;
  }

  {
    // we're no longer waiting for events
    std::scoped_lock lock{m_mutex};
    m_waiting = false;
  }

  Thread::testCancel();
}

IEventQueueBuffer::Type XWindowsEventQueueBuffer::getEvent(Event &event, uint32_t &dataID)
{
  std::scoped_lock lock{m_mutex};

  // push out pending events
  flush();

  // get next event
  XNextEvent(m_display, &m_event);

  // process event
  if (m_event.xany.type == ClientMessage && m_event.xclient.message_type == m_userEvent) {
    dataID = static_cast<uint32_t>(m_event.xclient.data.l[0]);
    return kUser;
  } else {
    event = Event(EventTypes::System, m_events->getSystemTarget(), &m_event);
    return kSystem;
  }
}

bool XWindowsEventQueueBuffer::addEvent(uint32_t dataID)
{
  // prepare a message
  XEvent xevent;
  xevent.xclient.type = ClientMessage;
  xevent.xclient.window = m_window;
  xevent.xclient.message_type = m_userEvent;
  xevent.xclient.format = 32;
  xevent.xclient.data.l[0] = static_cast<long>(dataID);

  // save the message
  std::scoped_lock lock{m_mutex};
  m_postedEvents.push_back(xevent);

  // if we're currently waiting for an event then send saved events to
  // the X server now.  if we're not waiting then some other thread
  // might be using the display connection so we can't safely use it
  // too.
  if (m_waiting) {
    flush();
    // Send a character through the round-trip pipe to wake a thread
    // that is waiting for a ConnectionNumber() socket to be readable.
    // The flush call can read incoming data from the socket and put
    // it in Xlib's input buffer.  That sneaks it past the other thread.
    ssize_t write_response = write(m_pipefd[1], "!", 1);

    // with linux automake, warnings are treated as errors by default
    if (write_response < 0) {
      // todo: handle read response
    }
  }

  return true;
}

bool XWindowsEventQueueBuffer::isEmpty() const
{
  std::scoped_lock lock{m_mutex};
  return (XPending(m_display) == 0);
}

EventQueueTimer *XWindowsEventQueueBuffer::newTimer(double, bool) const
{
  return new EventQueueTimer;
}

void XWindowsEventQueueBuffer::deleteTimer(EventQueueTimer *timer) const
{
  delete timer;
}

void XWindowsEventQueueBuffer::flush()
{
  // note -- m_mutex must be locked on entry

  // flush the posted event list to the X server
  for (auto &event : m_postedEvents) {
    XSendEvent(m_display, m_window, False, 0, &event);
  }
  XFlush(m_display);
  m_postedEvents.clear();
}