libzmq/doc/zmq_setsockopt.txt

zmq_setsockopt(3)
=================


NAME
----

zmq_setsockopt - set 0MQ socket options


SYNOPSIS
--------
*int zmq_setsockopt (void '*socket', int 'option_name', const void '*option_value', size_t 'option_len');*


DESCRIPTION
-----------
The _zmq_setsockopt()_ function shall set the option specified by the
'option_name' argument to the value pointed to by the 'option_value' argument
for the 0MQ socket pointed to by the 'socket' argument. The 'option_len'
argument is the size of the option value in bytes.

The following options are defined:


ZMQ_HWM: Set high water mark
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_HWM' option shall set the high water mark for the _message queue_
associated with the socket.  The high water mark is a hard limit on the number
of outstanding messages in the queue; if this limit has been reached the socket
shall enter an "emergency" state and depending on the socket type, 0MQ shall
take appropriate action such as blocking or dropping new messages entering the
queue.

The default 'ZMQ_HWM' value of zero means "no limit".

Option value type:: int64_t
Option value unit:: messages
Default value:: 0
Applicable socket types:: all


ZMQ_LWM: Set low water mark
~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_LWM' option shall set the low water mark for the _message queue_
associated with the socket.  This option only makes sense when used in
conjunction with the 'ZMQ_HWM' option. A socket which has reached it's high
water mark remains in the "emergency" state until the number of outstanding
messages in it's associated message queue falls below the low water mark, at
which point normal message processing is resumed.

Option value type:: int64_t
Option value unit:: messages
Default value:: 0
Applicable socket types:: all


ZMQ_SWAP: Set disk offload size
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_SWAP' option shall set the disk offload (swap) size for the _message
queue_ associated with the socket. A socket which has 'ZMQ_SWAP' set to a
non-zero value may exceed it's high water mark; in this case outstanding
messages shall be offloaded to storage on disk rather than held in memory.

The value of 'ZMQ_SWAP' defines the maximum size of the swap space in bytes.

Option value type:: int64_t
Option value unit:: bytes
Default value:: 0
Applicable socket types:: all


ZMQ_AFFINITY: Set I/O thread affinity
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_AFFINITY' option shall set the I/O thread affinity for connections
created by subsequent _zmq_connect()_ or _zmq_bind()_ calls on the specified
'socket'.

sockets. Affinity determines which threads from the 0MQ I/O thread pool
associated with the socket's _context_ shall handle newly created connections.
A value of zero specifies no affinity, meaning that work shall be distributed
fairly among all 0MQ I/O threads in the thread pool. For non-zero values, the
lowest bit corresponds to thread 1, second lowest bit to thread 2 and so on.
For example, a value of 3 specifies that subsequent connections on 'socket'
shall be handled exclusively by I/O threads 1 and 2.

See also linkzmq:zmq_init[3] for details on allocating the number of I/O
threads for a specific _context_.

Option value type:: int64_t
Option value unit:: N/A (bitmap)
Default value:: 0
Applicable socket types:: N/A


ZMQ_IDENTITY: Set socket identity
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_IDENTITY' option shall set the identity of the socket. Socket identity
determines if existing 0MQ infastructure (_message queues_, _forwarding
devices_) shall be identified with a specific application and persist across
multiple runs of the application.

If the socket has no identity, each run of an application is completely
separate from other runs. However, with identity set the socket shall re-use
any existing 0MQ infrastructure configured by the previous run(s). Thus the
application may receive messages that were sent in the meantime, _message
queue_ limits shall be shared with previous run(s) and so on.

Identity should be at least one byte and at most 255 bytes long. Identities
starting with binary zero are reserved for use by 0MQ infrastructure.

Option value type:: binary data
Option value unit:: N/A
Default value:: NULL
Applicable socket types:: all


ZMQ_SUBSCRIBE: Establish message filter
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_SUBSCRIBE' option shall establish a new message filter on a 'ZMQ_SUB'
socket. Newly created 'ZMQ_SUB' sockets shall filter out all incoming messages,
therefore you should call this option to establish an initial message filter.

An empty 'option_value' of length zero shall subscribe to all incoming
messages. A non-empty 'option_value' shall subscribe to all messages beginning
with the specified prefix. Mutiple filters may be attached to a single
'ZMQ_SUB' socket, in which case a message shall be accepted if it matches at
least one filter.

Option value type:: binary data
Option value unit:: N/A
Default value:: N/A
Applicable socket types:: ZMQ_SUB


ZMQ_UNSUBSCRIBE: Remove message filter
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_UNSUBSCRIBE' option shall remove an existing message filter on a
'ZMQ_SUB' socket. The filter specified must match an existing filter previously
established with the 'ZMQ_SUBSCRIBE' option. If the socket has several
instances of the same filter attached the 'ZMQ_UNSUBSCRIBE' option shall remove
only one instance, leaving the rest in place and functional.

Option value type:: binary data
Option value unit:: N/A
Default value:: N/A
Applicable socket types:: ZMQ_SUB


ZMQ_RATE: Set multicast data rate
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_RATE' option shall set the maximum send or receive data rate for
multicast transports such as linkzmq:zmq_pgm[7] using the specified 'socket'.

Option value type:: uint64_t
Option value unit:: kilobits per second
Default value:: 100
Applicable socket types:: all, when using multicast transports


ZMQ_RECOVERY_IVL: Set multicast recovery interval
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_RECOVERY_IVL' option shall set the recovery interval for multicast
transports such as linkzmq:zmq_pgm[7] using the specified 'socket'. The
recovery interval determines the maximum time in seconds that a receiver can be
absent from a multicast group before unrecoverable data loss will occur.

CAUTION: Excersize care when setting large recovery intervals as the data
needed for recovery will be held in memory. For example, a 1 minute recovery
interval at a data rate of 1Gbps requires a 7GB in-memory buffer.

Option value type:: uint64_t
Option value unit:: seconds
Default value:: 10
Applicable socket types:: all, when using multicast transports


ZMQ_MCAST_LOOP: Control multicast loopback
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_MCAST_LOOP' option shall control whether data sent via multicast
transports can also be received by the sending host via loopback.  A value of
zero disables the loopback functionality, while the default value of 1 enables
the loopback functionality. Leaving multicast loopback enabled when it is not
required can have a negative impact on performance. Where possible, disable
'ZMQ_MCAST_LOOP' in production environments.

Option value type:: uint64_t
Option value unit:: boolean
Default value:: 1
Applicable socket types:: all, when using multicast transports


ZMQ_SNDBUF: Set kernel transmit buffer size
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_SNDBUF' option shall set the underlying kernel transmit buffer size
for the socket to the specified size in bytes.  A value of zero means leave the
OS default unchanged. For details please refer to your operating system
documentation for the 'SO_SNDBUF' socket option.

Option value type:: uint64_t
Option value unit:: bytes
Default value:: 0
Applicable socket types:: all


ZMQ_RCVBUF: Set kernel receive buffer size
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_RCVBUF' option shall set the underlying kernel receive buffer size for
the socket to the specified size in bytes.  A value of zero means leave the OS
default unchanged. For details refer to your operating system documentation for
the 'SO_RCVBUF' socket option.

Option value type:: uint64_t
Option value unit:: bytes
Default value:: 0
Applicable socket types:: all


RETURN VALUE
------------
The _zmq_setsockopt()_ function shall return zero if successful. Otherwise it
shall return `-1` and set 'errno' to one of the values defined below.


ERRORS
------
*EINVAL*::
The requested option _option_name_ is unknown, or the requested _option_len_ or
_option_value_ is invalid.

*ETERM*::
The associated context was terminted.


EXAMPLE
-------
.Subscribing to messages on a 'ZMQ_SUB' socket
----
/* Subscribe to all messages */
rc = zmq_setsockopt (socket, ZMQ_SUBSCRIBE, "", 0);
assert (rc == 0);
/* Subscribe to messages prefixed with "ANIMALS.CATS" */
rc = zmq_setsockopt (socket, ZMQ_SUBSCRIBE, "ANIMALS.CATS", 12);
----

.Setting I/O thread affinity
----
int64_t affinity;
/* Incoming connections on TCP port 5555 shall be handled by I/O thread 1 */
affinity = 1;
rc = zmq_setsockopt (socket, ZMQ_AFFINITY, &affinity, sizeof affinity);
assert (rc);
rc = zmq_bind (socket, "tcp://lo:5555");
assert (rc);
/* Incoming connections on TCP port 5556 shall be handled by I/O thread 2 */
affinity = 2;
rc = zmq_setsockopt (socket, ZMQ_AFFINITY, &affinity, sizeof affinity);
assert (rc);
rc = zmq_bind (socket, "tcp://lo:5555");
assert (rc);
----


SEE ALSO
--------
linkzmq:zmq_socket[3]
linkzmq:zmq[7]


AUTHORS
-------
The 0MQ documentation was written by Martin Sustrik <sustrik@250bpm.com> and
Martin Lucina <mato@kotelna.sk>.