One ZeroMQ socket per thread or per call?

Question

As we all know, a ZeroMQ socket shall not be shared among application threads.
context_t instances however can.

I have a multi-threaded-application a

Answer 1

Here is my (current) solution, in C++11 you can assign object to a thread_local-storage. Storing the socket_t-instance static and thread_local in a function gives me the functionality I was looking for:

class socketPool
{
    std::string endpoint_;

public:
    socketPool(const std::string &ep) : endpoint_(ep) {}

    zmq::socket_t & operator()()
    {
        thread_local static zmq::socket_t socket(
                globalContext(), 
                ZMQ_REQ);
        thread_local static bool connected;

        if (!connected) {
            connected = true;
            socket.connect(endpoint_);
        }

        return socket;
    }
};

// creating a pool for each endpoint
socketPool httpReqPool("ipc://http-concentrator");

In my sendMessage()-function instead of creating and connecting I simply do

bool sendMessage(std::string s)
{
    zmq::socket_t &socket = httpReqPool();

    // the rest as above
}

Regarding performance, well, it's 7 times faster on my machine. (140k REQ/REP per second).