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 ØMQ 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 ØMQ 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, ØMQ 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 ØMQ 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 ØMQ 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 ØMQ 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 ØMQ 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 ØMQ 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 ØMQ 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 ØMQ documentation was written by Martin Sustrik <sustrik@250bpm.com> and Martin Lucina <mato@kotelna.sk>.