The problem is reproducible if you try to connect to the inactive server on localhost(or 127.0.0.1).

Open pvio_socket.c. The following call of getaddrinfo returns linked list of two items: IPv6 and IPv4 addresses

 /* Get the address information for the server using getaddrinfo() */

    wait_gai= 1;

    while ((gai_rc= getaddrinfo(cinfo->host, server_port,

                                &hints, &res)) == EAI_AGAIN)

    {

Then a new socket is created for each item in the list:

for (save_res= res; save_res; save_res= save_res->ai_next)

    {

      csock->socket= socket(save_res->ai_family, save_res->ai_socktype, 

                            save_res->ai_protocol);

And attempt to connect:

rc= pvio_socket_connect_sync_or_async(pvio, save_res->ai_addr, (uint)save_res->ai_addrlen);

But when the error handling is made, only the last created socket is closed:

/* close socket: MDEV-10891 */

  if (csock->socket != INVALID_SOCKET)

  {

    closesocket(csock->socket);

    csock->socket= INVALID_SOCKET;

  }

While the previous (IPv6 in that case) remains not freed, which can be easily checked with lsof:

$ lsof -p 95552 | grep CLOSED
ClientApp 95552 sergey 18u IPv6 0x9bc9e6ea54fa1537 0t0 TCP localhost:64829->localhost:mysql (CLOSED)

If multiple attempts are made the resource limit will be exceeded.