Socket logic problem

[Gabriel Genellina]

En Sat, 24 Oct 2009 06:40:08 -0300, John O'Hagan <research at johnohagan.com>  
escribió:

> I have several instances of the same generator function running
> simultaneously, some within the same process, others in separate  
> processes. I
> want them to be able to share data (the dictionaries passed to them as
> arguments), in such a way that instances designated as "leaders" send  
> their
> dictionaries to "follower" instances.
>
> I'm trying to use sockets to relay the dicts in pickled form, like this:
>
> from socket import socket
>
> PORT = 2050
> RELAY = socket()
> RELAY.bind(('', PORT))
> RELAY.listen(5)
>
> PICKLEDICT = ''
> while 1:
>     INSTANCE = RELAY.accept()[0]
>     STRING = INSTANCE.recv(1024)
>     if STRING == "?":
>         INSTANCE.send(PICKLEDICT)
>     else:
>         PICKLEDICT = STRING
>
> What I was hoping this would do is allow the leaders to send their dicts  
> to
> this socket and the followers to read them from it after sending an  
> initial
> "?", and that the same value would be returned for each such query until  
> it
> was updated.
>
> But clearly I have a fundamental misconception of sockets, as this logic  
> only
> allows a single query per connection, new connections break the old  
> ones, and
> a new connection is required to send in a new value.

You may use sockets directly, but instead of building all infrastructure  
yourself, use a ThreadingTCPServer (or ForkingTCPServer), they allow for  
simultaneous request processing. Even setting up a SimpleXMLRPCServer  
(plus either ThreadingMixIn or ForkingMixIn) is easy enough.

> Are sockets actually the best way to do this? If so, how to set it up to  
> do
> what I want? If not, what other approaches could I try?

See the wiki page on distributed systems:  
http://wiki.python.org/moin/DistributedProgramming

-- 
Gabriel Genellina