[Twisted-Python] Threading examples...

[Andrew Bennetts]

On Tue, Mar 23, 2004 at 03:58:20PM -0700, William McLendon wrote:
> Thanks,
> 
> So, now my example looks like this:
> 
> import time
> from twisted.internet import reactor
> 
> def aSillyBlockingMethod(x):
>    time.sleep(2)
>    print x
>    reactor.callFromThread(reactor.stop)
> 
> # run method in thread
> reactor.callInThread(aSillyBlockingMethod, "2 seconds have passed")
> 
> 
> It still just hangs... I have to go kill it from another window after 
> getting its pid from ps.   Am I doing the reactor.stop thing correctly?

Heh.  I just noticed the real bug: that example doesn't call reactor.run(),
either.

Complete, working example:

----
import time
from twisted.internet import reactor

def aSillyBlockingMethod(x):
   time.sleep(2)
   print x
   reactor.callFromThread(reactor.stop)

# run method in thread
reactor.callInThread(aSillyBlockingMethod, "2 seconds have passed")

reactor.run()
----

That reactor.callInThread starts the thread when the reactor isn't running yet
is probably a bug in Twisted.

> Basically, I have an application that talks via a http interface to a user 
> and I need to spawn off and do stuff from time to time.  I'm still learning 
> how all the reactor eventloops and whatnot work.  I ran into a problem 
> where I'm trying to run something via 
> twisted.internet.protocol.ProcessProtocol and serve its results up from 
> within a reactor.listentTCP() page handler ... but it blew up.  So, I'm 

How did it blow up (and how are you spawning the process)?  Twisted is quite
capable of coping with this -- it's how the CGI support in twisted.web
works.

> thinking that I could maybe just fork it off and run that way.  I've been 
> trying to figure out how the reactors() work and the threading and whatnot 
> the last few days but am kind of finding little help in the docs and google 
> that is at my level of understanding... seems most of the stuff is snippets 
> and pieces that assume you already see the big picture :-(  Any help here 
> is greatly appreciated ;-)

I strongly advise avoiding threads unless you really need them.  From your
description of what you are trying to do, you don't need them.

-Andrew.