[zeromq-dev] will receive fail if TCP goes down in REQ socket

[Justin Karneges]

Cool. Is there a reason the relaxed behavior is to close and reconnect 
in order to reset the state? I'd think all you'd need to do here is 
change a local state variable in the client and just reuse the same 
connection. As it stands, I'd still want to roll my own REQ over a 
DEALER socket unless I'm missing something.

On 12/13/2013 10:24 PM, Pieter Hintjens wrote:
> The ZMQ_REQ_RELAXED option on ZeroMQ v4, lets you resend requests.
>
> On Sat, Dec 14, 2013 at 3:46 AM, Justin Karneges <justin at affinix.com> wrote:
>> ZeroMQ does not resend messages, so while the reconnect/queuing logic
>> will protect you to some degree, you still need to account for message loss.
>>
>> If you're using REQ then you'll need to timeout the request, otherwise
>> if a request or response message is lost then you'll never be able to
>> make a request on the socket ever again. So don't just indefinitely
>> block on a send or receive. Further, ZeroMQ historically hasn't had a
>> way to get a REQ socket out of the "waiting for response" state in the
>> event of a timeout other than by closing the socket and starting over.
>> This means the REQ type is not really usable in production. Better to
>> use DEALER and format a REQ-compatible message yourself. REP does not
>> suffer from these problems, so you can keep on using that and have
>> DEALER talk to REP.
>>
>> Note: it is possible that very recent versions of ZeroMQ allow REQ
>> sockets to revert state on error but I haven't been following this closely.
>>
>> On 12/13/2013 04:17 PM, Sean Robertson wrote:
>>> I believe the REQ will simply wait for the REP to come back up,
>>> re-bind and send something.
>>>
>>> On Fri, Dec 13, 2013 at 2:53 PM, Mohit Jaggi <mohitjaggi at gmail.com> wrote:
>>>> Hi,
>>>> In most ZMQ sockets, the underlying TCP socket can change transparently.
>>>> Does that apply to REQ-REP sockets as well? Or will the receive call to ZMQ
>>>> socket fail?
>>>>
>>>> sock = new REQ socket;
>>>> connect(sock);
>>>> while(1) {
>>>> request = receive(...);
>>>> ...
>>>> send(response);
>>>> }
>>>>
>>>> For example in the above code, let us say that the server with REP socket on
>>>> the other side crashed and restarted. What will happen?
>>>>
>>>> Thanks,
>>>> Mohit.
>>>>
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