[zeromq-dev] HWM behaviour & blocking

Justin Karneges justin at affinix.com
Thu Jun 28 07:50:16 CEST 2012

On Thursday, May 10, 2012 01:53:48 PM Pieter Hintjens wrote:
> On Thu, May 10, 2012 at 3:44 PM, Paul Colomiets <paul at colomiets.name> wrote:
> > Can you be more specific, why setting HWM to 1 is a bad thing? Do you
> > mean, that it smells bad to set HWM to 1 for reliability? Or do you
> > think that setting it will have other consequences? (low performance?)
> it's bad because you're trying to force a synchronous model on an
> asynchronous system, and doing it at the wrong level. If you really
> want synchronization you MUST get some upstream data from the
> receiver. Just throttling the sender cannot work reliably.

I'm about to set HWM to 1 and I recalled a thread about this so I've looked it 
up. Totally agree about what's been said so far. The reason I want to do this 
is because I need a way for an event-driven application to determine if data 
has been written to the underlying kernel. This is useful in case the 
application wants to close the socket immediately after writing data. In a 
traditional blocking application, this is easy: just call zmq_close() and 
it'll unblock when done. However, in an event-driven application, the only way 
I can think of imitating this functionality is by setting HWM to 1 and waiting 
until ZMQ_EVENTS indicates writability, then calling zmq_close().


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