Danny,
I want to thank you for ruining my plans for a relaxing Saturday morning. As
a thread newbie I killed several hours playing around with your code.
One thing I noticed is that sometimes the program would hang, which I figured
was the Queue code blocking in the Ticket claim function. I used exception
handling to deal with that situation cleanly.
I then decided that it wasn't very nice of Starbucks to close after accepting
my order without giving me my Latte, so I changed that part of the code to:
def schedule(self,job):
"""Schedules a job and returns a "ticket" the user can later use
to get the result."""
if self.acceptNew == True:
outputQueue=Queue()
self.queue.put((job,outputQueue))
return Ticket(outputQueue)
else:
print "Server not accepting any new requests."
return None
def scheduleShutdown(self):
"""Add a job that shuts the system down."""
print "Telling server to shut down"
self.queue.put((Server._QUIT_NICELY,None))
def _jobLoop(self):
"""Continue looping through tasks."""
while True:
print "Looping ... "
(nextJob, outputQueue) = self.queue.get()
if nextJob is server._QUIT_NOW:
return
if nextJob is server._QUIT_NICELY:
self.acceptNew = False
self.queue.put((Server._QUIT_NOW,None))
else:
returnValue=self._doJob(nextJob)
outputQueue.put(returnValue)
I am 99.44% sure that this is thread safe, reasoning being:
setting the acceptNew to False and adding the QUIT_NOW happens in the
same
thread so it is impossible for another job to get scheduled after the
QUIT_NOW - so no thread will end up hanging...
However, I would sleep a little better if you could reassure me that I am
right, and would sleep even better if you could give me a method to test
this. This kinda stuff looks tricky to test with standard unittest
methodology....
Thanks again for the enligntenment all you guys bring to this awesome
language.
My bastardized code is below for reference.
--Todd Maynard < [EMAIL PROTECTED] >
[It is] best to confuse only one issue at a time.
-- K&R
**************************************
from threading import Thread
from Queue import Queue,Empty
class Ticket(object):
"""A small token we can use to claim our result."""
def __init__(self, q):
self.q = q
self.result = None
self.done=False
def claim(self):
if not self.done:
try:
self.result=self.q.get(True,5)
self.done=True
except Empty:
print "We lost the server!"
self.result=None
return self.result
class Server(object):
_QUIT_NOW=['Quit!']
_QUIT_NICELY=['Quit Nicely']
def __init__(self):
"""A queue will contain 2-tuples of (job, outputQueue)
elements."""
self.queue=Queue()
self.acceptNew=True
def startServer(self):
"""Brings the server online."""
Thread(target=self._jobLoop).start()
def schedule(self,job):
"""Schedules a job and returns a "ticket" the user can later use
to get the result."""
if self.acceptNew == True:
outputQueue=Queue()
self.queue.put((job,outputQueue))
return Ticket(outputQueue)
else:
print "Server not accepting any new requests."
return None
def scheduleShutdown(self):
"""Add a job that shuts the system down."""
print "Telling server to shut down"
self.queue.put((Server._QUIT_NICELY,None))
def _jobLoop(self):
"""Continue looping through tasks."""
while True:
print "Looping ... "
(nextJob, outputQueue) = self.queue.get()
if nextJob is server._QUIT_NOW:
return
if nextJob is server._QUIT_NICELY:
self.acceptNew = False
self.queue.put((Server._QUIT_NOW,None))
else:
returnValue=self._doJob(nextJob)
outputQueue.put(returnValue)
def _doJob(self,job):
print "I'm doing " , job
return job + job #Something to show that we are doing something
def separateCaller(server):
for i in range(1000,1004+1):
print " -- separateCaller asks %d" % i
ticket = server.schedule(str(i))
if ticket:
print " -- separateCaller got %s" % ticket.claim()
else:
print " -- separateCaller couldn't get a ticket."
if __name__=="__main__":
server = Server()
server.startServer()
Thread(target=separateCaller, args=(server,)).start()
result1=server.schedule("1")
result2=server.schedule("2")
result3=server.schedule("3")
if result3:
print "result3: %s" % result3.claim()
else:
print "result3: Couldn't get a ticket"
if result2:
print "result2: %s" % result2.claim()
else:
print "result2: Couldn't get a ticket"
if result1:
print "result1: %s" % result1.claim()
else:
print "result1: Couldn't get a ticket"
server.scheduleShutdown()
_______________________________________________
Tutor maillist - Tutor@python.org
http://mail.python.org/mailman/listinfo/tutor
