path: root/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 socket options can be set with the _zmq_setsockopt()_ function:


ZMQ_HWM: Set high water mark
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_HWM' option shall set the high water mark for the specified 'socket'.
The high water mark is a hard limit on the maximum number of outstanding
messages 0MQ shall queue in memory for any single peer that the specified
'socket' is communicating with.

If this limit has been reached the socket shall enter an exceptional state and
depending on the socket type, 0MQ shall take appropriate action such as
blocking or dropping sent messages. Refer to the individual socket descriptions
in linkzmq:zmq_socket[3] for details on the exact action taken for each socket
type.

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

[horizontal]
Option value type:: uint64_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 specified
'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.

[horizontal]
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 newly created
connections on the specified 'socket'.

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_.

[horizontal]
Option value type:: uint64_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 specified 'socket'.
Socket identity determines if existing 0MQ infrastructure (_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.

[horizontal]
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. Multiple 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.

[horizontal]
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.

[horizontal]
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'.

[horizontal]
Option value type:: int64_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 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: Exercise 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.

[horizontal]
Option value type:: int64_t
Option value unit:: seconds
Default value:: 10
Applicable socket types:: all, when using multicast transports


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

[horizontal]
Option value type:: int64_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.

[horizontal]
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.

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


ZMQ_LINGER: Set linger period for socket shutdown
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_LINGER' option shall set the linger period for the specified 'socket'.
The linger period determines how long pending messages which have yet to be
sent to a peer shall linger in memory after a socket is closed with
linkzmq:zmq_close[3], and further affects the termination of the socket's
context with linkzmq:zmq_term[3]. The following outlines the different
behaviours:

* The default value of '-1' specifies an infinite linger period. Pending
  messages shall not be discarded after a call to _zmq_close()_; attempting to
  terminate the socket's context with _zmq_term()_ shall block until all
  pending messages have been sent to a peer.

* The value of '0' specifies no linger period. Pending messages shall be
  discarded immediately when the socket is closed with _zmq_close()_.

* Positive values specify an upper bound for the linger period in milliseconds.
  Pending messages shall not be discarded after a call to _zmq_close()_;
  attempting to terminate the socket's context with _zmq_term()_ shall block
  until either all pending messages have been sent to a peer, or the linger
  period expires, after which any pending messages shall be discarded.

[horizontal]
Option value type:: int
Option value unit:: milliseconds
Default value:: -1 (infinite)
Applicable socket types:: all


ZMQ_RECONNECT_IVL: Set reconnection interval
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_RECONNECT_IVL' option shall set the reconnection interval for the
specified 'socket'.  The reconnection interval is the maximum period 0MQ shall
wait between attempts to reconnect disconnected peers when using
connection-oriented transports.

NOTE: The reconnection interval may be randomized by 0MQ to prevent
reconnection storms in topologies with a large number of peers per socket.

[horizontal]
Option value type:: int
Option value unit:: milliseconds
Default value:: 100
Applicable socket types:: all, only for connection-oriented transports


ZMQ_BACKLOG: Set maximum length of the queue of outstanding connections
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_BACKLOG' option shall set the maximum length of the queue of
outstanding peer connections for the specified 'socket'; this only applies to
connection-oriented transports. For details refer to your operating system
documentation for the 'listen' function.

[horizontal]
Option value type:: int
Option value unit:: connections
Default value:: 100
Applicable socket types:: all, only for connection-oriented transports.


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 0MQ 'context' associated with the specified 'socket' was terminated.
*EFAULT*::
The provided 'socket' was not valid (NULL).
*EINTR*::
The operation was interrupted by delivery of a signal.


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:5556");
assert (rc);
----


SEE ALSO
--------
linkzmq:zmq_getsockopt[3]
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>.