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

[Cameron Simpson]

On 13Feb2010 17:22, exarkun at twistedmatrix.com <exarkun at twistedmatrix.com> wrote:
| On 04:43 pm, maligree at 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 at zip.com.au> DoD#743
http://www.cskk.ezoshosting.com/cs/

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