[xcb] XCB polling and single-threadedness

Jamey Sharp xcb@nickle.org
07 Jul 2002 02:33:24 -0700

Hey all!

Good job, Andy. Unfortunately, XCBReadPacket doesn't work the way you
think it does. Sorry. :) I've added some comments in an attempt to make
future readers think it works the way it does. :)

For a complete XCBPollEvent implementation - which I need for XCL
anyway, so I'm glad this came up - it should also cause a non-blocking
read of the socket. XCBWait won't do, because it calls select and asks
it to wait forever. XCBReadEvent won't do, because (and here was the
confusion) it never accesses the socket at all.

As it happens, PollEvent can work without this non-blocking read - I've
updated test/main.c to call it occasionally - but applications may fail
in mysterious ways until it's fixed.

The best solution is probably to make the select timeout parameter be
passed to XCBWait. Current callers would pass a 0 there, while PollEvent
would pass the address of a struct indicating a 0 second timeout.
Perhaps you could take care of this too, Andy?



On Sat, 2002-07-06 at 18:58, Andy Howe wrote:
> XCBGenericEvent *XCBPollEvent(XCBConnection *c);
> If there are any events currently in the queue, the first event is
> returned. Otherwise, a null pointer is returned. Basicly, it works the
> same as XCBWaitEvent() except it returns null instead of waiting for an
> event if there is not one currently in the queue.
Jamey Sharp <jamey@sharp.ath.cx> - http://jamey.is.dreaming.org/