Help with fixing x2x...

[Harold L Hunt II]

Thomas,

In x2x, the return value from ProcessEvent which indicates that 
everything went normally is False, not True.  The real intentions for 
the return value of ProcessEvent can be described by the boolean 
variable called ``bAbortedDisconnect'' that is returned from 
ProcessMotionNotify.  Much more on that below but for now,

Ohmygodthatisfunny!!!

In the loop, the code does this:

1) Check for an event on fromDpy.  XPending returns immediately.

2) Process the event for fromDpy if an event was pending.  If we 
processed an event successfully, continue looping.  Else, the 
ProcessEvent function returned True and we are supposed to shutdown, 
thus the ``break''.

3) Check for an event on toDpy.  XPending returns immediately.

4) Process the event for toDpy if an event was pending.  If we processed 
an event successfully, continue looping.  Else, the ProcessEvent 
function returned True and we are supposed to shutdown, thus the ``break''.

5) Else, if we did not process an event from either screen, wait until 
one or both o fthe file handles that represent the display event queues 
becomes ready for reading.

I think that your infinite loop has to do with the fact that XPending 
returns a count of events ready for reading in fromPending, rather than 
a boolean value.  I think that (!fromPending) had the desired effect on 
the developer's platform of determining that (fromPending == 0), but 
that is a highly compiler-dependent assumption on behalf of the original 
developer.

For clarity, I would rewrite the section as follows (notice the 
correction in the ``else if''):

====================================================================
while (True) /* FOREVER */
   {
     /* Save the number of event ready for fromDpy */
     fromPending = XPending(fromDpy);

     /* Process any events ready for fromDpy */
     if (fromPending != 0)
       if (ProcessEvent(fromDpy, &dpyInfo)) /* shutdown if True! */
         break;

     /* Process any events ready for toDpy */
     if (XPending(toDpy))
       {
         if (ProcessEvent(toDpy, &dpyInfo)) /* shutdown if True! */
           break;
       }
     else if (fromPending == 0)
       {
         /* No events ready for either display.  Wait for an event. */
         FD_ZERO(fdset);
         FD_SET(fromConn, fdset);
         FD_SET(toConn, fdset);
         select(nfds, fdset, NULL, NULL, NULL);
       }
   } /* END FOREVER */
====================================================================

Now, for the excitement about the bAbortedDisconnect variable from 
ProcessMotionNotify:

It looks like the original programmer is using some sort of consistency 
checking on MotionNotify events to determine that the X server is 
shutting down.  I will have to look into this further, but it looks 
promising from my initial inspection.  This is the final step that I 
need for xwinclip to function properly on server resets and shutdowns. 
Needless to say, hopefully I am seeing what I want to see :)

Harold



Thomas Chadwick wrote:
> I recently discovered that when I run x2x, the Win2k Task Manager 
> reports that it's using 90-99% of the CPU.
> 
> While I have not noticed a slow down in performance when it's running, 
> I'd like to fix it if I can.  I've poked around in the source and I 
> don't like the looks of the main loop:
> 
>  while (True) { /* FOREVER */
>    if (fromPending = XPending(fromDpy))
>      if (ProcessEvent(fromDpy, &dpyInfo)) /* done! */
>     break;
> 
>    if (XPending(toDpy)) {
>      if (ProcessEvent(toDpy, &dpyInfo)) /* done! */
>     break;
>    } else if (!fromPending) {
>      FD_ZERO(fdset);
>      FD_SET(fromConn, fdset);
>      FD_SET(toConn, fdset);
>      select(nfds, fdset, NULL, NULL, NULL);
>    }
> 
> It would appear to me that this constant polling for an event to process 
> is what's eating up the CPU cycles.
> 
> Not being an X programmer, I'm hoping someone monitoring the list can 
> suggest a way to modify this loop to be less of a CPU hog.
> 
> Thanks.
> 
> 
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