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
