ZMQ_FILTER socket option added

This option is a performance tweak. In devices XSUB socket filters
the messages just to send them to XPUB socket which filters them
once more. Setting ZMQ_FILTER option to 0 allows to switch the
filtering in XSUB socket off.

Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

1 files changed, 18 insertions, 1 deletions

diff --git a/doc/zmq_getsockopt.txt b/doc/zmq_getsockopt.txt
index 97b4032..b48b06b 100644
--- a/doc/zmq_getsockopt.txt
+++ b/doc/zmq_getsockopt.txt
@@ -297,7 +297,7 @@ Applicable socket types:: all
 ZMQ_MULTICAST_HOPS: Maximum network hops for multicast packets
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-The option shell retrieve time-to-live used for outbound multicast packets.
+The option shall retrieve time-to-live used for outbound multicast packets.
 The default of 1 means that the multicast packets don't leave the local network.
 
 [horizontal]
@@ -307,6 +307,23 @@ Default value:: 1
 Applicable socket types:: all, when using multicast transports
 
 
+ZMQ_FILTER: Switches message filtering on or off
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The option shall retrieve the filtering behaiour of the socket.
+If 1, messages are filtered according to subcriptions as expected.
+If 0, messages are not filtered. This is a performance tweak. If a device
+receives a message from XSUB socket and it is about to send it to XPUB socket
+immediately, filtering would be done twice. We can thus turn off filtering in
+XSUB socket and rely on filtering in XPUB socket.
+
+[horizontal]
+Option value type:: int
+Option value unit:: boolean
+Default value:: 1
+Applicable socket types:: ZMQ_SUB, ZMQ_XSUB
+
+
 ZMQ_FD: Retrieve file descriptor associated with the socket
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 The 'ZMQ_FD' option shall retrieve the file descriptor associated with the