[zeromq-dev] One socket per thread or per call?

[Luca Boccassi]

On Mon, 2017-01-30 at 23:22 +0100, Patrick Boettcher wrote:
> Hi all,
> 
> I'm new to zmq and still discovering things and I'd like your feedback
> on a design decision.
> 
> (I asked the same question on StackOverflow, before seeing that there
> is a zmq-mailing list. 
> http://stackoverflow.com/questions/41941702/one-zeromq-socket-per-thread-or-per-call)
> 
> As we all know, a ZeroMQ socket shall not be shared between application
> threads. Contexts however can.
> 
> I have a multi-threaded-application and I'd like to have each thread
> exchange messages from time to time with a REP-socket (event, exceptions
> and the like) depending what they are doing (they are doing
> non-ZeroMQ-stuff).
> 
> To send messages to my REP-socket I use the following function
> (half-C++ half-pseudo-code):
> 
>   bool sendMessage(std::string s)
>   {
>       zmq::socket_t socket(globalContext(), ZMQ_REQ);
>       socket.connect(ETT::IPC::httpV1ConcentratorEndpoint);
> 
>       zmq::message_t message(s.size());
>       memcpy(message.data(), s.data(), s.size());
>       if (!socket.send(message))
>           return false;
> 
>       // poll on socket for POLLIN with timeout
> 
>       socket.recv(&message);
>       // do something with message
> 
>       return true;
>   }
> 
> This function is called from every thread when needed. It creates a
> local socket, connects, sends the message, and receives a response.
> At exit, the socket is disconnected and removed (at least I'm
> assuming that it is closed).

That's the C++ bindings so not sure, but libzmq does not close anything
for you, you have to do it explicitly

> This way, I don't need to bother to maintain a socket in each of my
> threads. This comes at the cost of creating and connecting each time I
> call this function.
> 
> I stressed this code and I don't see much difference between reusing
> one socket and this reconnect-implementation. (I have 20k REP-REQ per
> second, including json-decode/encode, in both cases)
> 
> Is there a more correct ZeroMQ-way of doing this?
> 
> best regards,
> --
> Patrick.

Closing and reopening sockets continuosly is an anti-pattern, I would
recommend opening a socket when the thread starts and closing it when
it's torn down

Kind regards,
Luca Boccassi
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