Provided by: libzmq-dev_2.2.0+dfsg-7_amd64 
NAME
zmq_setsockopt - set 0MQ socket options
SYNOPSIS
int zmq_setsockopt (void *socket, int option_name, const void *option_value, size_t option_len);
Caution: All options, with the exception of ZMQ_SUBSCRIBE, ZMQ_UNSUBSCRIBE and ZMQ_LINGER, only take
effect for subsequent socket bind/connects.
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 zmq_socket(3) for details on the exact action taken for each socket
type.
The default ZMQ_HWM value of zero means "no limit".
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 its 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 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 zmq_init(3) for details on allocating the number of I/O threads for a specific context.
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.
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.
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_RCVTIMEO: Maximum time before a recv operation returns with EAGAIN
Sets the timeout for receive operation on the socket. If the value is 0, zmq_recv(3) will return
immediately, with a EAGAIN error if there is no message to receive. If the value is -1, it will block
until a message is available. For all other values, it will wait for a message for that amount of time
before returning with an EAGAIN error.
Option value type int
Option value unit milliseconds
Default value -1 (infinite)
Applicable socket types all
ZMQ_SNDTIMEO: Maximum time before a send operation returns with EAGAIN
Sets the timeout for send operation on the socket. If the value is 0, zmq_send(3) will return
immediately, with a EAGAIN error if the message cannot be sent. If the value is -1, it will block until
the message is sent. For all other values, it will try to send the message for that amount of time before
returning with an EAGAIN error.
Option value type int
Option value unit milliseconds
Default value -1 (infinite)
Applicable socket types all
ZMQ_RATE: Set multicast data rate
The ZMQ_RATE option shall set the maximum send or receive data rate for multicast transports such as
zmq_pgm(7) using the specified socket.
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.
Option value type int64_t
Option value unit seconds
Default value 10
Applicable socket types all, when using multicast transports
ZMQ_RECOVERY_IVL_MSEC: Set multicast recovery interval in milliseconds
The ZMQ_RECOVERY_IVL_MSEC option shall set the recovery interval, specified in milliseconds (ms) for
multicast transports using the specified socket. The recovery interval determines the maximum time in
milliseconds that a receiver can be absent from a multicast group before unrecoverable data loss will
occur.
A non-zero value of the ZMQ_RECOVERY_IVL_MSEC option will take precedence over the ZMQ_RECOVERY_IVL
option, but since the default for the ZMQ_RECOVERY_IVL_MSEC is -1, the default is to use the
ZMQ_RECOVERY_IVL option value.
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.
Option value type int64_t
Option value unit milliseconds
Default value -1
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.
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.
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
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 zmq_close(3), and further affects the termination of the socket’s context with 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.
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 initial reconnection interval for the specified socket. The
reconnection interval is the 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.
Option value type int
Option value unit milliseconds
Default value 100
Applicable socket types all, only for connection-oriented
transports
ZMQ_RECONNECT_IVL_MAX: Set maximum reconnection interval
The ZMQ_RECONNECT_IVL_MAX option shall set the maximum reconnection interval for the specified socket.
This is the maximum period 0MQ shall wait between attempts to reconnect. On each reconnect attempt, the
previous interval shall be doubled untill ZMQ_RECONNECT_IVL_MAX is reached. This allows for exponential
backoff strategy. Default value means no exponential backoff is performed and reconnect interval
calculations are only based on ZMQ_RECONNECT_IVL.
Note
Values less than ZMQ_RECONNECT_IVL will be ignored.
Option value type int
Option value unit milliseconds
Default value 0 (only use ZMQ_RECONNECT_IVL)
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.
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.
ENOTSOCK
The provided socket was invalid.
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
zmq_getsockopt(3) zmq_socket(3) zmq(7)
AUTHORS
This manual page was written by the 0MQ community.