What is happening to my process?

Question

Hello,

I'm executing a SSH process like so:

checkIn()
sshproc = subprocess.Popen([command], shell=True)
exit = os.waitpid(sshproc.pid, 0)[1]
checkOut()

Its important that the process form checkIn() and checkOut() actions before and after these lines of code. I have a test case that involves that I exit the SSH session by closing the terminal window manually. Sure enough, my program doesn't operate correctly and checkOut() is never called in this case. Can someone give me a pointer into what I can look in to fix this bug?

Let me know if any other information would helpful.

Thanks!

Answer 1

The Python process would normally execute in the same window as the ssh subprocess, and therefore be terminated just as abruptly when you close that window -- before getting a chance to execute checkOut. To try and ensure that a function gets called at program exit (though for sufficiently-abrupt terminations, depending on your OS, there may be no guarantees), try Python standard library module atexit.

Answer 2

Perhaps all you need is a try ... finally block?

try:
    checkIn()
    sshproc = subprocess.Popen([command], shell=True)
    exit = os.waitpid(sshproc.pid, 0)[1]
finally:
    checkOut()

Unless the system crashes, the process receives SIGKILL, etc., checkOut() should be called.