Work around for LIBZMQ-496 The problem is that other threads might still be in mailbox::send() when it is destroyed. So as a workaround, we just acquire the mutex in the destructor. Therefore the running send will finish before the mailbox is destroyed.
Work around for LIBZMQ-496 The problem is that other threads might still be in mailbox::send() when it is destroyed. So as a workaround, we just acquire the mutex in the destructor. Therefore the running send will finish before the mailbox is destroyed.

trevorbernard/jeromq,fredoboulo/jeromq,trevorbernard/jeromq,fredoboulo/jeromq,c-rack/jeromq,zeromq/jeromq,zeromq/jeromq