Bug 808

Summary:

Xt: XtAppAddInput additional input sometimes ignored in multi-threaded application

Product:

xorg

Reporter:

Andreas Luik <luik>

Component:

Lib/Xt

Assignee:

Xorg Project Team <xorg-team>

Status:

RESOLVED FIXED

QA Contact:

Xorg Project Team <xorg-team>

Severity:

normal

Priority:

high

CC:

alan.coopersmith, eich, roland.mainz

Version:

unspecified

Keywords:

patch

Hardware:

x86 (IA32)

OS:

Linux (All)

Whiteboard:

i915 platform:

i915 features:

Attachments:

Description	Flags
mttest test program (gzipped tar file)	none
context diff to lib/Xt/NextEvent.c, either workaround of fix	none

Description Andreas Luik 2004-06-29 06:24:24 UTC

The X Toolkit does not call the callback function registered with
XtAppAddInput when there is some input pending on the registered file
descriptor, unless an X event has recently been processed.  This can
easily been reproduced with the attached test program.

The program consists of three threads:

- main thread: initialization, makes a pipe, registers the pipe[0] fd
as additional input, creates two other threads and runs the X Toolkit
main loop (XtAppNextEvent and XtDispatchEvent).

- WorkThread: endless loop, which calls XQueryTree and then sleeps for
three seconds.

- SignalWaiterThread: handles SIGINT signal using sigwait(), and
writes to pipe[1] when a signal has arrived.

When SIGINT is catched, the input callback for pipe[0] should be
called, but most of the time, it is not.  You can enforce the callback
to be called by generating an X event, e.g. by using the command
"xmodmap -e 'pointer = default'".

Comment 1 Andreas Luik 2004-06-29 06:29:14 UTC

Created attachment 428 [details]
mttest test program (gzipped tar file)

How to use the test program:

Compile the attached mttest.c program using the Imakefile.
Run it with "./mttest".
Press the INTR character several times.  Observe that the signal
handler is called, but the additional input is not recognized.	The
output is:

pascal:/(162)> ./mttest 
pipe 4
Work is active ...
./mttest: [signal waiter]: signal 2
./mttest: [signal waiter]: signal 2
./mttest: [signal waiter]: signal 2
./mttest: [signal waiter]: signal 2
...

Whereas it should be:

pascal:/(162)> ./mttest 
pipe 4
Work is active ...
./mttest: [signal waiter]: signal 2
ReadControlConnectionCB
./mttest: received SIGN 2

./mttest: [signal waiter]: signal 2
ReadControlConnectionCB
./mttest: received SIGN 2

./mttest: [signal waiter]: signal 2
ReadControlConnectionCB
./mttest: received SIGN 2

...

Comment 2 Andreas Luik 2004-06-29 06:34:50 UTC

Created attachment 429 [details] [review]
context diff to lib/Xt/NextEvent.c, either workaround of fix

With this patch applied to NextEvent.c, the bug seems to not occur.  Might
have a small performance penalty, because the fdlist is now rebuild more
often.	On the other hand, I think this might be required, because
select() modifies the fd_sets ...

Comment 3 Roland Mainz 2004-07-19 16:28:13 UTC

Comment on attachment 429 [details] [review]
context diff to lib/Xt/NextEvent.c, either workaround of fix

alan/egbert:
Do you know anyone who is able to review the patch ?

Comment 4 Erik Andren 2006-04-25 07:25:57 UTC

Ping!

Comment 5 Daniel Stone 2007-02-27 01:23:40 UTC

Sorry about the phenomenal bug spam, guys.  Adding xorg-team@ to the QA contact so bugs don't get lost in future.

Comment 6 Daniel Stone 2007-04-07 14:44:06 UTC

committed, not quite three years later.  thanks for the patch!

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