pwpsend() call are not not blocking. They only send a message and don't expect any response. pwprecv() and friends are though. It would indeed be a better idea to make them non blocking using poll()/select() (that would be up to the user implementation then).

About the network request queue, I though about it as well. Some recommendation advise no more than 10 request queued to avoid complex overhead. Not sure how to implement this properly though.

I'm definitely not for adding fork()/pthread_create() calls IN the library. This should be the user's choice to do so. But we could indeed design the library around it, using pwppreparereq() + pwpsendreq(), and let the user decide when he wants to send the messages.