Problem: reimplemented zmq_proxy_steerable control socket type is not
backwards compatible - replies are always sent.
In the past, zmq_proxy_steerable never sent a reply for
commands that weren't STATISTICS, so only really worked with PAIR and didn't
work at all with REP. Now it only supports REP and PAIR semantics changed. This
breaks compatibility with PAIR in a subtle and slightly annoying way if
HWMs are hit without reading the replies.
Solution: Add a check to send the empty reply only for
REP control sockets. This restores backwards compatibility, and supports
REP, PAIR, and SUB (for non-reply commands).
I had no knowledge of the pre-MPL-2.0 implementation. This fix is based
on docs and prior API usage. I contribute this under MPL-2.0.
It is contriubted under the MPL-2.0.
I had no knowledge of the previous implementation of zmq_proxy_steerable().
This version was developed based on expectations set in the old man page with one exception. This version uses a REP/REQ for the proxy control protocol sockets. The old man page example used PUB/SUB which is nonsensical given the STATISTICS command requires two way communication.
Solution: remove the implementation. Thijs Terlouw <thijsterlouw@gmail.com>,
the author, did not respond to requests to allow relicensing to MPL2,
so we have to remove his copyrighted work.
Remove the implementation and make get/set return -EOPNOTSUPP.
Solution: remove implementation. Laurent Alebarde <l.alebarde@free.fr>,
the author, did not respond to requests to allow relicensing to MPL2,
so we have to remove his copyrighted work.
Make the API into an empty stub that returns -EOPNOTSUPP.
Solution: Replace incorrect underline pattern in zmq_udp.txt that
makes part of the text show up as pre-formatted code block with
regular underline pattern.
zmq_ppoll mostly mimics zmq_poll behavior, except for the added feature of being able to specify a signal mask. Signals in this mask will be blocked during execution of zmq_ppoll. Switching of the process' active signal mask happens atomically with the actual poll call, so that no race conditions can occur. This behavior is useful when one wants to gracefully handle POSIX signals without race conditions. See e.g. the discussion below https://250bpm.com/blog:12/ for an explanation.
Also includes two new tests:
1. test_zmq_ppoll_fd does the same thing as test_zmq_poll_fd, demonstrating backwards compatibility with zmq_poll when used with a default signal mask.
2. test_zmq_ppoll_signals demonstrates the use of zmq_ppoll with a signal mask, blocking out SIGTERM everywhere except in zmq_ppoll, allowing to handle the signal in one place without having to worry about race conditions.
This is important in order to send the login sequence of a client to the server.
Solution: add ZMQ_HICCUP_MSG to a socket, socket would send that message whenever a connection get temporarly disconnected
* Problem: No direct support for setting socket priority
Solution: Add ZMQ_PRIORITY socket option, which sets the
SO_PRIORITY socket option on the underlying socket. This
socket option is not supported under Windows. Check option
and set socket option on creation of underlying socket.
Fixed three things:
1. Moved asterisks by variable names into the single quotes (to match [zmq_poll](https://github.com/zeromq/libzmq/edit/master/doc/zmq_init.txt) and other pages.)
2. Fixed variable name in example.
3. Fixed extra & in example.
ZMQ_ROUTER_NOTIFY doesn't have a context and doesn't play nice with protocols. with ZMQ_DISCONNECT_MSG we can set it to a protocol message, like DISCONNECT in majordomo. Router will send it when a peer is disconnected. Another advantage of ZMQ_DISCONNECT_MSG is that it also works on inproc.
Together with ZMQ_HEARTBEAT it allows to build very reliable protocols, and much simpler as well.
When using ZMQ_HEARTBEAT one still needs to implement application-level heartbeat in order to know when to send a hello message.
For example, with the majordomo protocol, the worker needs to send a READY message when connecting to a broker. If the connection to the broker drops, and the heartbeat recognizes it the worker won't know about it and won't send the READY msg.
To solve that, the majordomo worker still has to implement heartbeat. With this new option, whenever the connection drops and reconnects the hello message will be sent, greatly simplify the majordomo protocol, as now READY and HEARTBEAT can be handled by zeromq.
* UDP is mentioned as available transport, and it also supports
wildcard addresses, but not mentioned
* zmq_unbind(7) also mentions about wild-card endpoint in zmq_bind(3)
Solution: add udp in wildcard address related docs
Solution: a new socket type, called PEER. Very similar to SERVER, but can only connect to other PEERs. Also a new zmq_connect_peer method, that connect and return a routing-id in thread-safe and atomic operation
