[zeromq-dev] How to detect if a remote socket has closed

[Matt Weinstein]

I use ZMQ_PAIR to push stuff off my reactor thread, for example if I  
have to steer certain message types.  For example, if inbound and  
outbound are the normal sockets, but there's something special that  
has to be done with some of the client requests:

[[ INBOUND_REACTOR ]] >> { if (special) push to pair; else push to  
outbound; }
[[ OUTBOUND_REACTOR ]]  >> {push reply to inbound}
[[ PAIR_REACTOR ]] >> { e.g. send special reply to inbound }

Also, you can push off functions like updates, aggregation, command  
and control etc., anything that has a stream at the other end from  
which you'll need a streamed set of replies.

It's helpful to keep stuff off the reactor thread.

In addition, you can use pairs to speak to endpoint controls, e.g. if  
you are brokering::

	[[ INBOUND_REACTOR]] >> {  request to pair(N) depending on type of  
request, etc. }
	[[ PAIR1_REACTOR ]] >> { push reply to inbound }
	[[ PAIR2_REACTOR ]] >> { ibid }
	...

Best,
Matt

On Aug 24, 2010, at 11:41 AM, <david.briant at ubs.com> <david.briant at ubs.com 
 > wrote:

> Just rereading this thread. Why shouldn't I be using pairs in normal
> code?
>
> I want to do simple point-to-point (often asynchronous) messaging
> between many peers. The REQ/REP and PUB/SUB paradigms don't fit.
> Additionally I want to do dynamic resource discovery which concretely
> binding to a port negates.
>
> Cheers
>
> David
>
> -----Original Message-----
> From: zeromq-dev-bounces at lists.zeromq.org
> [mailto:zeromq-dev-bounces at lists.zeromq.org] On Behalf Of Pieter
> Hintjens
> Sent: Tue 17-Aug-2010 17:05
> To: 0MQ development list
> Subject: Re: [zeromq-dev] How to detect if a remote socket has closed
>
> On Tue, Aug 17, 2010 at 5:04 PM,  <David.Briant at ubs.com> wrote:
>
>> 1) Can I check that all socket types are meant to rebind
> automatically.
>
> All except ZMQ_PAIR, which you should not be using in normal code
> anyhow.
>
>> 2) Also the REQ socket appears to cause python to use 100% cpu if the
>> REP socket isn't running. I assume that shouldn't be the case?
>
> Definitely not healthy.  So I just booted Windows XP and tried the
> Hello World client and server from the guide, in Python.  Started the
> hwclient.py, watched CPU.  Killed it, then started hwserver.py.  In
> neither case was there any CPU usage (task manager itself takes 1% or
> so).
>
>> So it looks like I should have a directory service that can mediate
> PAIR
>> connections between peers, I need a SUB connection to the directory
> and
>> a REQ connection to initially connect to it on a well known port. The
>> directory a service is registered with PUBs any state changes such as
>> service crashes. It will also PUB a restart (of itself) on the same
>> channel. The only situation I don't have covered is if a directory
> crash
>> means the directory starting on a different IP but a slow heartbeat
>> mechanism should sort that.
>>
>> Do you recommend PGM for the PUB/SUB part? - initially there'll only
> be
>> a few apps so TCP might be fine.
>
> Don't take this the wrong way, but I'd really suggest you read through
> the user guide chapters 1 and 2 and work through all the examples
> until they are clear.  They're all simple C programs.
>
> Then, start by solving a small part of your problem and get that
> working.  Then, extend that carefully one piece at a time.
>
> -
> Pieter Hintjens
> iMatix - www.imatix.com
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