Re: Different behavior with multiprocessing
On Tue, Mar 5, 2013 at 1:31 AM, Tomas Kotal tomas.ko...@gmail.com wrote: But when I run same script on Linux, what I get is this: 0 32512 Under Unix, the return value from os.system() encodes more than one piece of information: http://docs.python.org/2/library/os.html#os.system http://docs.python.org/2/library/os.html#os.wait 32512 is 127*256, meaning that the shell exited with return code 127 when given an unrecognized command. ChrisA -- http://mail.python.org/mailman/listinfo/python-list
Re: Different behavior with multiprocessing
Under Unix, the return value from os.system() encodes more than one piece of information: http://docs.python.org/2/library/os.html#os.system http://docs.python.org/2/library/os.html#os.wait 32512 is 127*256, meaning that the shell exited with return code 127 when given an unrecognized command. ChrisA Well the point is not the difference between return values of os.system under Windows and Linux. The point is that I set the exist code of child process with os._exit() which works fine on Windows but on Linux the process.exitcode returns always 0. What is very strange is, that if I set return code to some other value, like: ... os._exit( len(cmd) ) ... Then I got exit codes 3 and 2 under Linux, which is correct. But when I do something like this: ... ret = os.system(cmd) print ret # this print real value, like 32512 os._exit(ret) # exitcode of this child process will be 0 on Linux ... It doesn't work, which seems very strange to me. -- http://mail.python.org/mailman/listinfo/python-list
Re: Different behavior with multiprocessing
Dne pondělí, 4. března 2013 15:31:41 UTC+1 Tomas Kotal napsal(a): Hi all. Recently I discovered a strange behavior with multiprocessing library and call to function os.system (a different behavior under Linux and Windows to be more specific). I have this simple testing script: import sys import os from multiprocessing import Process def do_fork(cmd): ret = os.system(cmd) # print result of call print ret os._exit(ret) if __name__ == __main__: cmds = [ dir, xy ] procs = [] for cmd in cmds: proc = Process(target=do_fork, args=(cmd, )) proc.start() procs.append( proc ) for proc in procs: proc.join() print exitcode: %d % proc.exitcode print ok This script just starts 2 processes. Each process executes one command in system shell and exits setting it's exit code same as exit code of a system call. There are 2 commands: dir (which works fine on Windows and Linux) and xy (which is supposed to fail under both systems). The strange thing is that when I run this script under Windows I get this output: 0 1 exitcode: 0 exitcode: 1 ok The first 0 and 1 are results of os.system call which are printed from child processes. Rest of lines are printed from main process. This is expected output. But when I run same script on Linux, what I get is this: 0 32512 exitcode: 0 exitcode: 0 ok Although the second command fails and returns exit code 32512, the exit code from process in parent process gives me 0. I tried to change the script to use fork() instead of Process but the result was same. Can anybody explain me what's the problem here? (I use Python 2.6 on both Windows and Linux machines) Seems like I found the problem: os._exit probably takes as parametr unsigned char, so it uses as error code whatever value it gets modulo 256: os._exit(1) # process.exitcode == 1 os._exit(255) # process.exitcode == 255 os._exit(256) # process.exitcode == 0 os._exit(257) # process.exitcode == 1 os._exit(32512) # process.exitcode == 0 So on Linux it's necesary to call something like this: os._exit( os.system(cmd) 8 ) Because the first byte of return value on Linux is number of signal which kills the process and the second one is actual exit code. http://docs.python.org/2/library/os.html#os.wait -- http://mail.python.org/mailman/listinfo/python-list
Re: Different behavior with multiprocessing
On Tue, Mar 5, 2013 at 2:35 AM, Tomas Kotal tomas.ko...@gmail.com wrote: Seems like I found the problem: os._exit probably takes as parametr unsigned char, so it uses as error code whatever value it gets modulo 256: os._exit(1) # process.exitcode == 1 os._exit(255) # process.exitcode == 255 os._exit(256) # process.exitcode == 0 os._exit(257) # process.exitcode == 1 os._exit(32512) # process.exitcode == 0 So on Linux it's necesary to call something like this: os._exit( os.system(cmd) 8 ) Because the first byte of return value on Linux is number of signal which kills the process and the second one is actual exit code. Yep. I had a reply part-written but you beat me to it! That is indeed what you need if you want to chain return values. However, why are you using os._exit? Check out the note here: http://docs.python.org/2/library/os.html#os._exit ChrisA -- http://mail.python.org/mailman/listinfo/python-list
