[ww-tedit-dev] implementation: timed WaitEvent under X Window

[petar marinov]

For a GUI to work appropriately most of the time a non-blocking function
that extracts events must be present in the interface library. X
Window's interface library offers XNextEvent(), XPeekEvent() and 
XPending(). This means that non-blocking extraction would involve a loop 
of peek and delay but it effectively lacks a timed non-blocking event 
function!

I resorted again to the advantage of the free software and peeked into 
the sources of FTE [2]. There I found that select() might be employed 
for monitoring any incoming activity. X works on top of sockets, xlib's 
ConnectionNumber() returns the ID of the socket. It all seems natural 
but the X programming book [1] didn't mention any of that, it would have 
been impossible to implement this by solely following the documentation.

code could be as simple as:

  if (XPending(pdisp))
    return TRUE;

  FD_ZERO(&rset);
  connection = ConnectionNumber(pdisp);
  FD_SET(connection, &rset);

  tv.tv_sec = 0;
  tv.tv_usec = SLEEP_TIME;

  n = select(connection + 1, &rset, NULL, NULL, &tv);

---

Most of the development of the X version of WW I've been doing in 
cygwin. On the same machine I also have ZoneAlarm installed. X uses 
sockets to communicate with the clients and it shows -- ZoneAlarm's 
traffic indicator reflects that.

I noticed that when I start WW the traffic indicator jumps to its 
fullest while any other X program is most of the time using very little 
of socket's bandwidth.

I checked on my wait-event() function (x_kbd.c). The SLEEP_TIME value 
was to be most likely the disturbing factor. It was set to 20ms. The 
main event loop relies on wait-event() and the only X function that is 
invoked in the interim is XPending(). I wouldn't expect that this one 
would generate a socket traffic. It is that or something else but when 
select() times out that soon the ZoneAlarm's indicator blows the roof.

I experimented with values for SLEEP_TIME. Once I move it above 30ms 
ZoneAlarm goes back to normal. I left it at 50ms.

-petar

[1] http://www.amazon.com/exec/obidos/tg/detail/-/1565920023
[2] http://fte.sourceforge.net/