Signal Handling - should I even try in Python?
Aaron Watters
Frank Kim wrote:
>
> Below is a simple program that demonstrates how I've tried to do signal
> handling in Python.
Well, after I fixed your syntax error to make the program work I couldn't
get it to show any problems. (on slowlarus... oops... solaris).
Guido is on vacation, but I believe his official advice is: avoid
using signals if possible. signals interact weirdly sometimes with
built in operations: eg, blocking network reads suppress signals
sometimes, because they are in the middle of initializing a data
structure that must be completed before the python main loop can
resume in a consistent state -- you can get around this by doing
horrible things like reading one character at a time, which is okay
unless you're reading megabytes...
That's all I can say, unless you can come up with a scenario
that clearly demonstrates your problem. maybe someone else knows...
-- Aaron Watters
===
A stitch in time breeds contempt.
Frank Kim
Below is a simple program that demonstrates how I've tried to do signal
handling in Python. As you can see I had to catch the IOError exception
so I exit gracefully. When I extended this idea to larger programs I
found myself trying to catch many exceptions and sometimes the program
wouldn't even exit. Does anyone have suggestions on how to properly do
signal handling? Thanks!
#!/usr/local/bin/python
# July 2, 1996
# Test catching signals.
import signal, time, sys
exitFlag = 0
def handler (signum, frame):
global exitFlag
print "howdy"
exitFlag = 1
def mysleep(secs): # could get even fancier...
done = 0
while not done:
try:
time.sleep(secs)
done = 1
except IOError:
pass
signal.signal (signal.SIGABRT, handler )
signal.signal (signal.SIGALRM, handler )
signal.signal (signal.SIGHUP, handler )
signal.signal (signal.SIGINT, handler )
signal.signal (signal.SIGQUIT, handler )
signal.signal (signal.SIGTERM, handler )
signal.signal (signal.SIGTSTP, handler )
while (1):
mysleep (1)
print "I'm sleeping."
if exitFlag == 1:
sys.exit()
--
Frank Kim fran...@catfish.lcs.mit.edu
http://cag-www.lcs.mit.edu/~frankkim/