[ python-Bugs-1015937 ] os.system segmentation fault

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Bugs item #1015937, was opened at 2004-08-25 08:25
Message generated for change (Settings changed) made by nnorwitz
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Category: Threads
Group: Python 2.3
>Status: Closed
>Resolution: Out of Date
Priority: 5
Submitted By: Tomasz Kowaltowski (kowaltowski)
Assigned to: Nobody/Anonymous (nobody)
Summary: os.system segmentation fault 

Initial Comment:
System used: Linux Fedora Core 2.
Python version: Python 2.3.3 (#1, May  7 2004, 10:31:40)
------------------------------------------------

Depending on the build used for Java, its invocation
through os.system within a thread causes a segmentation
fault. The attached short program illustrates this problem.

Any Java class 'DoNothing.class' (also attached) in the
current directory will do. Notice that only the second
one of the two builds 04 and 05 causes this problem.

It migh be a Java problem but I tried the same thing
with pthreads in C, and no problems occured.

-- Tomasz Kowaltowski


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Comment By: Tomasz Kowaltowski (kowaltowski)
Date: 2004-09-08 19:52

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I guess so even though 2.4 is still alpha.

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Comment By: Raymond Hettinger (rhettinger)
Date: 2004-09-08 14:56

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So, can this be closed as "out-of-date"?

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Comment By: Tomasz Kowaltowski (kowaltowski)
Date: 2004-09-08 14:45

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Tested with the alpha version Python-2.4a3. It works properly!

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Comment By: Tomasz Kowaltowski (kowaltowski)
Date: 2004-08-26 07:26

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I did not find the file 'thread_pthread.h' under my
installation :-(.  My program in C is:

----------------------------------------------------------
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>

void *ExecuteCommand( void *ptr ) {
  char *command = ptr;
  int result = system(command);
  printf("Tested the command: %s; result =
%d\n",command,result);
  return NULL;
 } 

int main()
{
  pthread_t thread;
  pthread_create(&thread,NULL,ExecuteCommand,
       (void*)"/usr/java/j2sdk1.4.2_04/bin/java -cp .
DoNothing");
  pthread_join(thread,NULL);
  pthread_create(&thread,NULL,ExecuteCommand,
       (void*)"/usr/java/j2sdk1.4.2_05/bin/java -cp .
DoNothing");
  pthread_join(thread,NULL);
  return 0;
}
----------------------------------------------------------

It correctly prints 0 for both threads.

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Comment By: Neal Norwitz (nnorwitz)
Date: 2004-08-26 00:37

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There's another possibility, but I'm not sure if it would
affect your build or not.  It's possible to set a smaller
stack size when creating a thread.  This would mean that
THREAD_STACK_SIZE is set.  If you look in
./Python/thread_pthread.h you will see the references. 
THREAD_STACK_SIZE is not set on my box.  

In your C test, did you pass NULL for the attributes or did
you do pthread_attr_init().  It's possible that is the
difference between your C test and python.  You might try
mucking in ./Python/thread_pthread.h to see if you can
determine what is happening.

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Comment By: Tomasz Kowaltowski (kowaltowski)
Date: 2004-08-25 20:04

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I tried all these things. Adding 'strace' to the command
line to be executed reports a segmentation fault which was
already expected because of the error code 11 printed by the
Python test program. 'ulimit -a' reports everything that
counts unlimited. I also tried Java memory options without
any success. You are right -- it is the java that is dying
not Python, but it only happens under this unusual circumstance.

It seems to me that if it were an environment problem it
would happen within any call of os.system. It happens
however only within Python threads: I tested both packages
'thread' and 'threading' and they both had the same
behavior. It does not happen if no threads are envolved, or
if threads are programmed in C.

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Comment By: Neal Norwitz (nnorwitz)
Date: 2004-08-25 18:02

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This sounds like an environment problem.  I'm guessing that
the stack is being blown and the kernel is killing the
process.  It's java that's dying, not python, correct?  

I don't have _05.  _04 works fine for me one Fedora 1.  Can
you use strace or gdb to try to determine what's happening?
 I'm not sure if anyone will be able to reproduce this
problem.  Can you also try starting java with options to
lower the the memory consumption, e.g., -Xss -Xmx.

>From your shell you can also try raising stack size, etc
with ulimit.  This may get java to run ok.  -s changes the
stack size.  BTW, what does ulimit -a report?

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