[Twisted-web] spawning a xvfb and firefox with a timeout

[Glyph Lefkowitz]

On Aug 19, 2011, at 12:42 AM, Stephan wrote:

> I'm attempting to spawn xvfb with firefox using twisted's spawnProcess.
> 
> I'm having two issues:
> 
> 1) when I call a normal process (not xvfb) it seems to work, but when I call xvfb the process goes defunct

Defunct processes have exited, but not been reaped.  In older versions of Twisted, this might happen if some other library were competing to register the SIGCHLD signal.  What version of Twisted are you using?

> 2) perhaps because it goes defunct but the timeout I set in place in the processprotocol does
> not trigger.

It should never go defunct, whether or not your timeout triggers.

> ==============
> here is the code for spawning a process
> ==============
> 108         command = ["/usr/bin/xvfb-run", "--auto-servernum",
> "/usr/bin/firefox", "-P", profile_id]
> 109         subprocess = reactor.spawnProcess(TimedProcessProtocol(20),
> 110                                             command[0], command)
> 111         logging.debug(type(subprocess))
> 112         logging.debug("spawned a process: pid: %d", subprocess.pid)
> 113
> 114         # this file will be created when firefox starts
> 115         while (not os.path.exists(self.profile_dir + "/importantfile")):
> 116             logging.debug("in while loop waiting for
> firesharkReady file to exist")
> 117             pass

You should really not busy-loop like this waiting for the subprocess.  Have a repeating callLater (or LoopingCall) that does this check cooperatively with the reactor, so if something goes wrong (for example: firefox fails to launch), you'll be able to react to it effectively rather than just hanging your Twisted process forever.  If firefox isn't actually starting correctly, or that file doesn't actually get created for some reason, this could cause the defunct process.

> 118
> 119         logging.debug("file exist")
> 
> ==============
> here is the process class
> ==============
> 
> 27 class TimedProcessProtocol(protocol.ProcessProtocol):
> 28
> 29     def __init__(self, timeout):
> 30         self.timeout = timeout
> 31
> 32     def connectionMade(self):
> 33         logging.debug("connection made timeout = %d", self.timeout)
> 34         @defer.inlineCallbacks
> 35         def killIfAlive():
> 36             logging.debug("timeout reached - killing process")
> 37             try:
> 38                 yield self.transport.signalProcess('KILL')
> 39             except error.ProcessExitedAlready:
> 40                 logging.debug("process already exited")
> 41                 pass
> 42
> 43         d = reactor.callLater(self.timeout, killIfAlive)
> 44
> 45     def outReceived(self, data):
> 46         logging.debug("output: %s", data)
> 47
> 48     def errReceived(self, data):
> 49         logging.debug("errReceived %s", data)
> 
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