Problem with spawning an external process

[Nico Kruger]

Apologies, this is on a Fedora Core 2 system.

On Wed, 2006-04-12 at 11:27, Nico Kruger wrote:
> I want to execute a command (in this case, and it seems to be
> significant, a Java program) in a thread in Python. When I execute the
> java binary in the main python thread, everything runs correctly. But
> when I try and execute java in a thread, java segfaults. I am using
> Python 2.3.3 and trying to run the java binary from the 1.4.2 SDK from
> Sun.
> 
> I have tried executing some arbitrary C program that I wrote, and it
> works fine in the main thread and the started thread. The problem seems
> to be specific to the Java binary.
> 
> Here is the example code:
> 
> --- START CODE ---
> import os
> import popen2
> import time
> import select
> import threading
> 
> # Change these to suit your system
> PATH = '/home/nico/j2sdk1.4.2/bin/java'
> #PATH = '/home/nico/j2sdk1.4.2/bin/java -invalid_arg'
> 
> def get_ret(status):
> 	signal = status & 0xff
> 	if signal == 0:
> 		retcode = status >> 8
> 	else:
> 		retcode = 0
> 	return signal,retcode
> 	
> print "In main thread"
> # Using spawn
> pid = os.spawnl(os.P_NOWAIT,PATH,PATH)
> ret = os.waitpid(pid,0)
> print "PID: %i  signal: %i   return code: %i" %
> (ret[0],get_ret(ret[1])[0],get_ret(ret[1])[1])
> 
> class TestThread(threading.Thread):
> 	def run(self):
> 		# Using spawn
> 		pid = os.spawnl(os.P_NOWAIT,PATH,PATH)
> 		ret = os.waitpid(pid,0)
> 		print "PID: %i  signal: %i   return code: %i" %
> (ret[0],get_ret(ret[1])[0],get_ret(ret[1])[1])
> 	
> print "In Thread"
> TestThread().start()
> 
> print "Waiting..."
> time.sleep(2)
> print "...Finished"
> ---- END CODE ----
> 
> Here is the output that I get on my machine:
> [nico@ script]$ python testcrash2.py
> In main thread
>        <JAVA USAGE INFO STRIPPED>
> PID: 32107  signal: 0   return code: 1
> In Thread
> PID: 32116  signal: 11   return code: 0
> 
> 
> You will notice that in the main thread, the program executes correctly
> (return code 1, signal 0). When the command is executed in the thread,
> it segfaults (signal 11). The second PATH= line calls Java with an
> invalid argument. In this case, it does not crash in the thread.
> 
> I have tried a fork() and then os.execv in the thread as well, and get
> the same behaviour.
> 
> I would appreciate it if someone with both Java and Python could try and
> run this sample and report back. Any suggestions would be welcome, as
> this is quite the showstopper for me at the moment. I am sure I am
> missing something totally obvious...
> 
> Thanks in advance,
> Nico.
> 



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