Segmentation Fault Catch

[Kurian O.S]

Hey Guys,

I have a python script and it will loop through bunch of maya files and do some stuff. But some time maya get seg fault and my script will stop there. I tried with signal and multiprocess. But both failed 

def sig_handler(signum, frame):

    pass

signal.signal(signal.SIGSEGV, sig_handler)  

from multiprocessing import Process, Queue

p = Process(target=startCrawling, args=(args, options))

    p.start()

    p.join()

Both failed.

Any other method which can trap seg fault and continue with next ?

Thanks

--

--:: Kurian ::--

[Marcus Ottosson]

Hi Kurian,

Do you mean you are running separate processes that open up Maya in the background to do some processing?

Have a look at subprocess.Popen, it runs a process completely separate from where you ran it from and shouldn't be affected by any of them crashing. They can also be run concurrenctly, by just running many of them at the same time. You'll be given a handle to the process where you can either communicate or just wait (join), similar to Process().

Best,

Marcus

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Marcus Ottosson
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[Kurian O.S]

I got a hint that I was using signal.signal(signal.SIGSEGV, sig_handler)   in wrong place. 

To view this discussion on the web visit https://groups.google.com/d/msgid/python_inside_maya/CAFRtmODZ1cvY2OFNCF0q6Yg1GMrNd6_y1bcepXF9mZhWkuddgg%40mail.gmail.com.

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--:: Kurian ::--

[Kurian O.S]

I was wrong its not working :(

def sig_handler(signum, frame):

    pass

def dosome(args, options):

    #here is my seg fault coming

    signal.signal(signal.SIGSEGV, sig_handler) 

    #maya functions goes here

if __name__ == "__main__":

    from multiprocessing import Process, Queue

    p = Process(target=dosome, args=(args, options))

        p.start()

        p.join()

This is my code

--

--:: Kurian ::--

[Justin Israel]

Hey Kurian,

I'm not clear on this from your code example, but are you using the multiprocessing module from within Maya? Your example indicates that it is a standalone script. First, I don't think it is safe to use the multiprocessing module within Maya, since forking is not a very safe thing to do in that environment. And second, if you are going to handle the seg fault yourself, you would be expected to exit the process afterwards (since you aren't really doing anything to fix the problem), otherwise you are just going to make it continue having problems. 

I think you should go the route that Marcus suggested, where you use subprocess. This will fork and exec a new process, instead of just forking your current image, which could lead to tons of problems in Maya.

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[Kurian O.S]

Hey Guys,

First its a command line tool using optparse to get arguments and options from user and using maya standalone to do some process ( running through mayapy ). So Some files its just fail to do the process. Subprocess I am not sure how I can call a function with arguments.

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For more options, visit https://groups.google.com/d/optout.

--

--:: Kurian ::--

[Justin Israel]

Well if you want to stick with the multiprocessing module and just endure the possible seg faults and some files not getting processed, you could print a warning and then do a os._exit(1) to just terminate the process.

Using subprocess, you could have your script take arguments, such as a -file flag to accept the file to process. When you run it without that particular flag it would start your batch operation, and then subprocesses can call the same executable again with specific -file options. Here would be a pretty crude example:

#!/usr/bin/env python

import sys
import subprocess

def process(f):
    print "process:", f

if __name__ == "__main__":
    if '-file' in sys.argv:
        process(sys.argv[-1])
        sys.exit()

    for names in ('foo', 'bar', 'baz'):
        cmd = [sys.argv[0], '-file', names]
        # cmd = [sys.executable, sys.argv[0], '-file', names]
        subprocess.Popen(cmd)

​

If your script is already executable, then you wouldn't need that commented line that runs it with "python <script>". 

You would want to actually do this in a bounded way, like using a thread pool or threads+queue to chew on your list of files to process.

Normally the multiprocessing module could work for what you are doing, but I think it isn't playing nice with Maya's initialized environment when the process forks. 

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[Kurian O.S]

I think I am confusing you all 

Here is a snippet

http://pastebin.com/J526ftrM

I tried my max to explain :)

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For more options, visit https://groups.google.com/d/optout.

--

--:: Kurian ::--

[Justin Israel]

That does explain what you are trying to do, thanks. It wasn't what I thought you were explaining.

Why do you need a Process for this? You create one process, and join on it. Why not just initialize maya standalone right before you are going to start the work and do it all in the original process?

As for the segfault, I don't think you can do what you are thinking. You usually can't just ignore a segfault and keep going unless you know how to fix the problem. The maya runtime might be in a bad state at this point and is expecting to crash, but you are catching that. It isn't like a type of Python exception that you can try/except and pass. Handling a SIGSEGV is normally something you do to either do a graceful exit, or for debugging purposes to examine the current state of the process.

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