[zeromq-dev] socket passing and thread safety.. a precise exlanation

Apostolis Xekoukoulotakis xekoukou at gmail.com
Fri Oct 19 15:08:18 CEST 2012

Ok, I think I did things correctly.

I am trying to inform the other threads(except the parent thread) of
updates that are sent from zookeeper. So I decided to use a pub/sub to
inform them of the changes, + router/dealer for the acknowledgements.

zookeeper only allows you to define functions that are triggered on
asynchronous events. So I'd have to create a new context inside such a
triggered event. I think I could do it. Passing the sockets,for now, might
be enough.

>Could you be more specific? I'll expand the zthread manual as needed.

I think I get confused because it introduces 3 concepts, the agent, the
zctx object and the pipe that is used to communicate between them.
I think that in the guide there is only the notion of the "context",
something you create at the beginning and then stop worrying about it.

>It must monitor its pipe, and exit if the

>  pipe becomes unreadable.

Also what does this mean? Monitoring the pipe means that I expect that a
msg will arrive. When It doesnt arrive, I will have to exit.
Does this also mean that I have to generate that msg? (heartbeat)

2012/10/19 Pieter Hintjens <ph at imatix.com>

> On Fri, Oct 19, 2012 at 8:16 AM, Apostolis Xekoukoulotakis
> <xekoukou at gmail.com> wrote:
> > I would like to know when it is possible to pass a socket without
> creating
> > problems?
> You're using CZMQ, I assume...?
> You can pass a socket from one thread to another if you do not use it
> in the original thread after you create the child thread (that acts as
> a full memory barrier). The child thread must close it.
> Are you sure you can't create the socket in the child thread where it
> belongs? You can use a separate context and a known TCP endpoint.
> > I create worker threads with zthread_fork (czmq) and I want that the pub
> > socket send messages to workers. Will this work? How can it work?
> Workers create SUB sockets and connect them to a tcp:// endpoint that
> is a PUB socket; whether it's another thread, process, or box, doesn't
> matter.
> If you want to use an inproc transport then you must ensure all
> threads get the same context. However you can still create the PUB
> socket in the thread that uses it, and then you must create it and
> bind it before you start the worker threads.
> > I would also like to point out that zthread manual contains information
> that
> > is not self complete, the missing parts are not contained in the guide.
> It
> > requires either knowledge of the internals of zeromq or (on threading in
> > general?).
> Could you be more specific? I'll expand the zthread manual as needed.
> -Pieter
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Sincerely yours,

     Apostolis Xekoukoulotakis
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