frodek@forit.forut.no (Frode Kileng) (04/18/91)
Configuration:
Sparc Station 1
Openwindows 2
Olwm.
I have a program for displaying X-ray images. The program has been up running
for a couple of months at this time. I'm now working with an audio expansion to
the program.
The audio part is set up to receive SIGIO interrupts when it is time to
read/write from/to the audio device. The program also receives
SIGALRM interrupts that I use to display the peek level of the audio and
to show record/play time. At each SIGALRM interrupt I send 1-2 draw requests
to the X server. The program run
Both the imaging part and the audio part work if I run them one at a time.
BUT it crash every time when I'm recording/playing and at the same time use
the imaging part. The program crashes with the different X error messages :
X Error BadRequest X Error: BadValue
Request Major code 254 () Request Major code 89 ()
Request Minor code 254 Request Minor code 0
ResourceID 0xa00028 ResourceID 0xa0002a
Error Serial #285 Error Serial #310
Current Serial #312 Current Serial #312
X Error: BadValue X Error BadLength
Request Major code 89 () ..............
Request Minor code 0 ..............
ResourceID 0xa0002a
Error Serial #310
Current Serial #312
Some times the program crash with no error messages at all.
My guess is that the program is doing a XLib call from the imaging part
and at the same time receives a SIGALRM interrupt
generating another XLib request before the first request is carried
through.
I will appreciate any help on this problem.
Frode Kileng
Frode.Kileng@fbt.tf.tele.no (frodek@forit.forut.no)mouse@lightning.mcrcim.mcgill.EDU (der Mouse) (05/02/91)
> I have a program for displaying X-ray images. The program has been > up running for a couple of months at this time. I'm now working with > an audio expansion to the program. > The audio part is set up to receive SIGIO interrupts when it is time > to read/write from/to the audio device. The program also receives > SIGALRM interrupts that I use to display the peek level of the audio > and to show record/play time. At each SIGALRM interrupt I send 1-2 > draw requests to the X server. Danger, danger. > Both the imaging part and the audio part work if I run them one at a > time. BUT it crash every time when I'm recording/playing and at the > same time use the imaging part. Yup. > My guess is that the program is doing a XLib call from the imaging > part and at the same time receives a SIGALRM interrupt generating > another XLib request before the first request is carried through. This is basically correct. Almost all implementations of Xlib do not contain code to interlock correctly with themselves when called both from signal handlers and from the code that can be interrupted by the signal. Basically, you have to make sure that you never make Xlib calls from within a signal handler that might have interrupted an Xlib call. (If you want to live dangerously: you probably can get away with this provided they do not share any Xlib data; in particular, they must not use the same Display connection.) How you arrange this is up to you. You can have the signal handler dump something in global variables for the main-line to notice and act on, you can use sigblock() to block delivery of the relevant signals while doing Xlib operations (I assume you have sigblock() because you have SIGIO), or anything else with the same result. Since you appear to be running under UNIX, you might consider forking and splitting responsibilities. But note that if you do that, the two processes cannot share a single display connection, not even if you take care that they don't both try to use it at once; each process that needs to do X operations must use its own connection. der Mouse old: mcgill-vision!mouse new: mouse@larry.mcrcim.mcgill.edu
janzen@mprgate.mpr.ca (Martin Janzen) (05/04/91)
In article <9105021507.AA18962@lightning.McRCIM.McGill.EDU>, mouse@lightning.mcrcim.mcgill.EDU (der Mouse) replies to a question which has already expired from my system, so I don't know the author... >> = ??? > = der Mouse >> [...] >> The audio part is set up to receive SIGIO interrupts when it is time >> to read/write from/to the audio device. The program also receives >> SIGALRM interrupts that I use to display the peek level of the audio >> and to show record/play time. At each SIGALRM interrupt I send 1-2 >> draw requests to the X server. > >Danger, danger. > >> Both the imaging part and the audio part work if I run them one at a >> time. BUT it crash every time when I'm recording/playing and at the >> same time use the imaging part. > >Yup. > >["der Mouse" goes on to explain that Xlib won't work in signal handlers] My suggestion would be to replace the signals and signal handlers entirely if possible, by using the built-in XtAddInput and XtAddTimeOut functions. At the least, you should be able to use XtAddTimeOut to set a timer which calls a procedure to update the display at regular intervals. You can use any Xlib calls you want in this procedure, since there's no SIGALRM involved. Also, you could try using XtAddInput to add a procedure which is called when- ever reads or writes are possible on the audio device. (It eventually calls select(), including your file descriptors in the read- and write-masks.) If your SIGIO handler just does buffering and doesn't need to make Xlib calls, this probably isn't necessary. Also, the response time requirements of the audio device may force you to use an interrupt handler. But if you can move all the drawing code into the XtTimerCallbackProc, your SIGIO handler should work. -- Martin Janzen janzen@mprgate.mpr.ca (134.87.131.13) MPR Teltech Ltd. Phone: (604) 293-5309 8999 Nelson Way Fax: (604) 293-5787 Burnaby, BC, CANADA V5A 4B5