[zeromq-dev] Hanging on client "receive" when a responder goes down in extended request-reply pattern (code in C#)

[Bruno D. Rodrigues]

At first glance I can’t see anything wrong with the code, but I have no idea how the NetMQ is implemented. According to the spec, and both the libzmq C code as well as the JeroMQ java implementations, I can assure you that the PUSH (and any other socket besides PUB and ROUTER) will block if the PULLs are busy. No message is ever lost except for the specific and documented cases on reconnect.

There is one option to define a send timeout, so maybe the default is different on NetMQ? Can you check the result of the send() operation and see if it returns any error, and which error?


On Jan 15, 2014, at 18:00, Chris Whiten <chris.whiten at gmail.com> wrote:

> That was my original thought, and what I had tried before being pointed to the pattern I originally described.  I've tried setting the high watermark, but this seems to just dictate how many messages the consumer should buffer before throwing messages away.  I haven't been able to find any options to coax the publisher into blocking when this limit is hit.
> 
> Here is my push/pull pattern code that I had tried: http://pastebin.com/CJLaY5zk
> 
> 
> On Wed, Jan 15, 2014 at 12:43 PM, Bruno D. Rodrigues <bruno.rodrigues at litux.org> wrote:
> Dumb question, but why not a simple PUSH/PULL pattern and no queues? Each consumer PULLs one message to process. The process pushing data (which may be more than one) will block when the HWM is hit (all consumers are busy, and the “queue” from the producer is full). No need for “hold-on-i’m-busy” messages, as PUSH-PULL does it already by themselves. 
> 
> 
> On Jan 15, 2014, at 16:29, Chris Whiten <chris.whiten at gmail.com> wrote:
> 
>> I'm using zeromq in a competing consumer setup, where one process is pushing data to a set of worker processes to parallelize some data processing.  
>> 
>> The publisher publishes data much more quickly than the workers can process it, so I want the publisher to block when all of the consumers are too busy.  I'll decide if they're too busy by having them pull data from zeromq and push them to an in-memory queue on each of the workers, and if that in-memory queue is too large we temporarily stop accepting messages from zeromq.
>> 
>> When all of the consumers are too busy, I wish for the client that is pushing data to the consumers to block, so we don't lose large chunks of data.  To solve that, I've set up the extended request-reply pattern (as outlined in Figure 16 of the zeromq guide at http://zguide.zeromq.org/page:all).  This seems to work in the happy case, but if a worker goes down the client will never receive a response back from that worker, and it will hang indefinitely.  Have I selected the wrong pattern, or is there an easy way to remedy this problem?
>> 
>> My code to test this is at http://pastebin.com/CaZpVayu
>> 
>> Thanks for your help
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