Asp Forum - Re: threading and signals - main thread solely responsible for signal handling?

Cameron Simpson

2/14/2010 1:37:00 AM

On 13Feb2010 17:22, exarkun@twistedmatrix.com <exarkun@twistedmatrix.com> wrote:
| On 04:43 pm, maligree@gmail.com wrote:
| >The main part of my script is a function that does many long reads
| >(urlopen, it's looped). Since I'm hell-bent on employing SIGINFO to
| >display some stats, I needed to run foo() as a seperate thread to
| >avoid getting errno 4 (interrupted system call) errors (which occur if
| >SIGINFO is received while urlopen is setting itself up/waiting for a
| >response). This does the job, SIGINFO is handled without ever brutally
| >interrupting urlopen.
| >
| >The problem is that after starting foo as a thread, my main thread has
| >nothing left to do - unless it receives a signal, and I am forced to
| >keep it in some sort of loop so that ANY signal handling can still
| >occur. I thought I'd just occupy it with a simple while 1: pass loop
| >but that, unfortunately, means 100% CPU usage.
[...]
|
| MRAB suggested you time.sleep() in a loop, which is probably fine.
| However, if you want to have even /less/ activity than that in the
| main thread, take a look at signal.pause().

Funnily enough I coded this issue just a few weeks ago, and my main
program looks like this:

def main(argv):
xit = 0
cmd = os.path.basename(argv[0])
SM = SystemManager()
[...set up a bunch of subsystems...]
SM.startAll()
try:
signal.pause()
except KeyboardInterrupt:
warn("KeyboardInterrupt interrupts pause()")
xit = 1
SM.close()
SM.join()
return xit

So SM.close() tells all the subsystems to close and finish up. That largely
involved putting the "EOF" sentinel value on a lot of Queues, causes the
subsystems to cease processing stuff. The separate SM.join() does the actaul
waiting for everything.

This makes for clean and timely shutdown for me.
--
Cameron Simpson <cs@zip.com.au> DoD#743
http://www.cskk.ezoshosti...

If your new theorem can be stated with great simplicity, then there
will exist a pathological exception. - Adrian Mathesis

comp.lang.python

Re: threading and signals - main thread solely responsible for signal handling?

Cameron Simpson

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