Mailman 3 February 2007 - Twisted

[Twisted-Python] Reactor getting stuck in random places on Windows?
by Steve Freitas Feb. 4, 2007

Feb. 4, 2007

I'm writing a Twisted client that uses PB. It seems to be getting stuck intermittently -- failing to respond to the server's queries. Sometimes it gets stuck immediately after login, sometimes after it's been running fine for a while. I'm starting the Twisted client in a terminal window. What unsticks it in these cases is always a single ^C. Now, sometimes that spits up an unhandled exception from some place into the log (stdout) and then it goes on its merry way -- other times it has no error to report and moves on like nothing happened. I'm frequently ctrl-C'ing this program as I try my new changes, and sometimes it takes one to kill it, and sometimes it takes two. Hopefully this is a clue. I thought perhaps I had a deferred that was hanging, but in the entire client, I'm calling addCallback() exactly once -- and it's followed by an addErrback(), so I don't think the problem is there. I first noticed this behavior when it was running as a Windows service, and I thought it may have been related to the necessity of starting the reactor with calling reactor.run(installSignalHandlers=0) (I didn't yet see the tip about periodically passing child signals to the reactor), but it still happens, albeit apparently less often, with a simple reactor.run(). Any ideas would be appreciated. Thanks, Steve

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[Twisted-Python] Problem: spawnProcess() never ending when installSignalHandlers=False
by Matt Feifarek Feb. 3, 2007

Feb. 3, 2007

Hello. I'm using Twisted 1.3.0 on python2.4 on an Ubuntu-Hoary x86 Linux box. I'm using twisted and spawnProcess() with a Queue structure to chain processes that need to be called (specifically, imagemagick commands). I use the "processEnded" event/method of t.i.p.ProcessProtocol to go from one task to the next. Twisted shares a python process with a multi-threaded web-app-kit (Webware) so it has to be run in a thread. This worked well on other older versions of twisted and older versions of python; also on linux. I've tracked down the problem to be twisted itself (or my incorrect use of it) rather than my code. This example illustrates it: ------------------------------------------------- from twisted.internet import reactor from twisted.internet.protocol import ProcessProtocol class MyProt( ProcessProtocol ): def processEnded(self, reason): print "ended.", reason executable = '/bin/touch' args = ( '/tmp/foo.txt', ) args = (executable,) + tuple(args) reactor.spawnProcess( MyProt(), executable, args ) reactor.callLater( 5, reactor.stop ) #reactor.run() reactor.run(installSignalHandlers=False) ------------------------------------------------- As is, this code never runs the "processEnded()" method of MyProt(). If I change the reactor.run() parameter to leave the signal handlers on, it works. Note that I need to leave the signal handlers turned off because I can't run the reactor in the main thread; Webware needs that. I also know that the subprocess is giving up its file descriptors; I can see that if I put more print statements into MyProt(). And I know that the subprocess is working; /tmp/foo.txt is there. It seems that somehow the reactor is using signals to notice when a process has ended; this makes a certain ammount of sense intuitively, though I don't understand the nitty-gritty of processes and signals at all. And more importantly, this has worked before on other combinations of twisted/python. Is this a bug? If so, has it been fixed? If not, what should I do to detect when a spawned process is finished? Thanks very much. Twisted rocks.

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[Twisted-Python] testing for error conditions
by gary jefferson Feb. 2, 2007

Feb. 2, 2007

I've got a little test program that checks to make sure my protocol behaves correctly. Each function returns a deferred, and sets the next function as the callback, and some common function as errback. This seems to work great -- the test runs through all the test funcs when working properly, and halts at the problem point if not. But now I want to verify that I get errors (errbacks) in all the places I should. I was hoping to do the same thing as before, only now swap the function of the errbacks with that of the callbacks. This doesn't seem to work. Returning a deferred from an errback still results in its parent errbacks getting called, terminating the test program prematurely. Whats the right way to test conditions that should trigger errbacks? I couldn't see a tutorial or doc that covered this. Thanks, Gary

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