I want to gracefully release some expensive system resource in my code with event handler. The problem is that the event handler is registered in a forked sub-process (yes, I have to put the event handler there in sub-process, since the resource is allocated after fork) and I want the sub-processes terminate when parent process dies. However, the code does not work as my expectation.
Here is a runnable example:
import time
import os
import signal
PRCTL=None
# get prctl from libc
def getPRCTL():
global PRCTL
if PRCTL is None:
import ctypes
PRCTL = ctypes.CDLL("libc.so.6")["prctl"]
return PRCTL
def dieWithParent():
prctl = getPRCTL()
prctl(1, signal.SIGTERM) # 1 = PR_SET_PDEATHSIG
def foo():
print "In foo."
def handler(signo, frame):
print "Handler is activated."
signal.signal(signal.SIGTERM, handler)
time.sleep(10) # in case sub-process terminates first.
if __name__ == '__main__':
dieWithParent()
pid = os.fork()
if 0 == pid:
foo()
else:
print "Subprocess spawned."
print "dying..."
The code does the following:
- instruct OS to turn parent die signal to a SIGTERM;
- fork a sub-process;
- if child process, register signal handler and wait for parent's termination.
On my platform, the output is
$ python main.py
In foo.
Subprocess spawned.
dying...
It seems the handler is not activated.
Anything wrong with my code or understanding?
Configuration on my box is
2.6.18-238.el5 x86_64 Python 2.6
Any hints will be highly appreciate, thank you!
