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 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 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
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.
- 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 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 specified 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 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 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 using the specified socket 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 0MQ context associated with the specified socket was terminated.
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
The 0MQ documentation was written by Martin Sustrik
<sustrik@250bpm.com[1]> and Martin Lucina <mato@kotelna.sk[2]>.
NOTES
- 1. sustrik@250bpm.com
- mailto:sustrik@250bpm.com
- 2. mato@kotelna.sk
mailto:mato@kotelna.sk