How can I keep a process spawned by Twisted spawnProcess running for a long time?

Question

I am new to Twisted. I encountered this problem recently and would like some help. As I understand, the twisted reactor runs as a single-threaded loop. When I spawn another process to get the input from the loop (and later on would pass the result back to the loop), the process just quits right after, even when no input is passed to it (see my code below).

Also, is it possible to keep ONE spawned process running for a long time as opposed to spawning a new process every time an input is received?

Thank You for your time,

Q

from sys import executable
from os import environ
import os
from twisted.internet import reactor
from twisted.internet.protocol import Protocol
from twisted.internet.protocol import Factory
from twisted.internet import protocol

implementation = """\
import os
print "in child", os.getpid()
"""

class Echo(Protocol):
    def dataReceived(self, data):
        reactor.spawnProcess(pp, executable, [executable, "-c", implementation], env=environ)
        self.transport.write(data)

class EchoFactory(Factory):
    def buildProtocol(self, addr):
        return Echo()

class MyPP(protocol.ProcessProtocol):

    def connectionMade(self):
        print "connectionMade!"
    def outReceived(self, data):
        print "out", data
    def errReceived(self, data):
        print "error", data
    def inConnectionLost(self):
        print "inConnectionLost! stdin is closed! (we probably did it)"
    def outConnectionLost(self):
        print "outConnectionLost! The child closed their stdout!"
    def errConnectionLost(self):
        print "errConnectionLost! The child closed their stderr."
    def processExited(self, reason):
        print "processExited, status %d" % (reason.value.exitCode,)
    def processEnded(self, reason):
        print "processEnded, status %d" % (reason.value.exitCode,)
        print "quitting"

reactor.listenTCP(8200, EchoFactory())
pp = MyPP()
print 'in parent', os.getpid()
reactor.spawnProcess(pp, executable, [executable, "-c", implementation], env=environ)
reactor.run()

score 2 · Answer 1 · answered Jun 06 '12 at 19:09

2

Twisted doesn't control when the child process exits. The child process is in charge of that (with one or two exceptions that don't matter here). Your child process, a Python program running this code:

import os
print "in child", os.getpid()

will exit as soon as it has printed its own PID. This is its behavior whether you launch it using Twisted or otherwise. If you want it to wait for input, then you have to add code for that to the program.

answered Jun 06 '12 at 19:09

Jean-Paul Calderone

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Is it possible to have a stream of data coming in, gets processed by the python program, then passed back to the parent without exiting the child process? – Squall Leohart Jun 06 '12 at 20:49
can you give me an example of how I would do that? For example, I would redirect what goes into the reactor loop to stdin. – Squall Leohart Jun 06 '12 at 21:16
1

isn't that the same as the question you asked at and at ? Having so many duplicates of the same question is a bad way to use stackoverflow. It wastes other people's time in providing the same answer multiple times. – Jean-Paul Calderone Jun 08 '12 at 12:08

How can I keep a process spawned by Twisted spawnProcess running for a long time?

1 Answers1