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);

Caution: All options, with the exception of ZMQ_SUBSCRIBE, ZMQ_UNSUBSCRIBE, ZMQ_LINGER, ZMQ_ROUTER_MANDATORY and ZMQ_XPUB_VERBOSE 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_SNDHWM: Set high water mark for outbound messages

The ZMQ_SNDHWM option shall set the high water mark for outbound messages on 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 for details on the exact action taken for each socket type.

Note	0MQ does not guarantee that the socket will accept as many as ZMQ_SNDHWM messages, and the actual limit may be as much as 60-70% lower depending on the flow of messages on the socket.

Option value type	int
Option value unit	messages
Default value	1000
Applicable socket types	all

ZMQ_RCVHWM: Set high water mark for inbound messages

The ZMQ_RCVHWM option shall set the high water mark for inbound messages on 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.

Option value type	int
Option value unit	messages
Default value	1000
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 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_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_IDENTITY: Set socket identity

The ZMQ_IDENTITY option shall set the identity of the specified socket when connecting to a ROUTER socket. The identity should be from 1 to 255 bytes long and MAY NOT start with binary zero.

If two clients use the same identity when connecting to a ROUTER, the ROUTER socket shall accept only the first such client and reject the others.

Option value type	binary data
Option value unit	N/A
Default value	NULL
Applicable socket types	ZMQ_REQ, ZMQ_REP, ZMQ_ROUTER, ZMQ_DEALER.

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 using the specified socket.

Option value type	int
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 milliseconds 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	int
Option value unit	milliseconds
Default value	10000
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	int
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	int
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, and further affects the termination of the socket’s context with zmq_term. 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. The value -1 means no reconnection.

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.

ZMQ_MAXMSGSIZE: Maximum acceptable inbound message size

Limits the size of the inbound message. If a peer sends a message larger than ZMQ_MAXMSGSIZE it is disconnected. Value of -1 means no limit.

Option value type	int64_t
Option value unit	bytes
Default value	-1
Applicable socket types	all

ZMQ_MULTICAST_HOPS: Maximum network hops for multicast packets

Sets the time-to-live field in every multicast packet sent from this socket. The default is 1 which means that the multicast packets don’t leave the local network.

Option value type	int
Option value unit	network hops
Default value	1
Applicable socket types	all, when using multicast transports

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_IPV4ONLY: Use IPv4-only sockets

Sets the underlying native socket type. A value of 1 will use IPv4 sockets, while the value of 0 will use IPv6 sockets. An IPv6 socket lets applications connect to and accept connections from both IPv4 and IPv6 hosts.

Option value type	int
Option value unit	boolean
Default value	1 (true)
Applicable socket types	all, when using TCP transports.

ZMQ_DELAY_ATTACH_ON_CONNECT: Accept messages only when connections are made

If set to 1, will delay the attachment of a pipe on connect until the underlying connection has completed. This will cause the socket to block if there are no other connections, but will prevent queues from filling on pipes awaiting connection.

Option value type	int
Option value unit	boolean
Default value	0 (false)
Applicable socket types	all, only for connection-oriented transports.

ZMQ_ROUTER_MANDATORY: accept only routable messages on ROUTER sockets

Sets the ROUTER socket behavior when an unroutable message is encountered. A value of 0 is the default and discards the message silently when it cannot be routed. A value of 1 returns an EHOSTUNREACH error code if the message cannot be routed.

Option value type	int
Option value unit	0, 1
Default value	0
Applicable socket types	ZMQ_ROUTER

ZMQ_XPUB_VERBOSE: provide all subscription messages on XPUB sockets

Sets the XPUB socket behavior on new subscriptions and unsubscriptions. A value of 0 is the default and passes only new subscription messages to upstream. A value of 1 passes all subscription messages upstream.

Option value type	int
Option value unit	0, 1
Default value	0
Applicable socket types	ZMQ_XPUB

ZMQ_TCP_KEEPALIVE: Override SO_KEEPALIVE socket option

Override SO_KEEPALIVE socket option(where supported by OS). The default value of -1 means to skip any overrides and leave it to OS default.

Option value type	int
Option value unit	-1,0,1
Default value	-1 (leave to OS default)
Applicable socket types	all, when using TCP transports.

ZMQ_TCP_KEEPALIVE_IDLE: Override TCP_KEEPCNT(or TCP_KEEPALIVE on some OS)

Override TCP_KEEPCNT(or TCP_KEEPALIVE on some OS) socket option(where supported by OS). The default value of -1 means to skip any overrides and leave it to OS default.

Option value type	int
Option value unit	-1,>0
Default value	-1 (leave to OS default)
Applicable socket types	all, when using TCP transports.

ZMQ_TCP_KEEPALIVE_CNT: Override TCP_KEEPCNT socket option

Override TCP_KEEPCNT socket option(where supported by OS). The default value of -1 means to skip any overrides and leave it to OS default.

Option value type	int
Option value unit	-1,>0
Default value	-1 (leave to OS default)
Applicable socket types	all, when using TCP transports.

ZMQ_TCP_KEEPALIVE_INTVL: Override TCP_KEEPINTVL socket option

Override TCP_KEEPINTVL socket option(where supported by OS). The default value of -1 means to skip any overrides and leave it to OS default.

Option value type	int
Option value unit	-1,>0
Default value	-1 (leave to OS default)
Applicable socket types	all, when using TCP transports.

ZMQ_TCP_ACCEPT_FILTER: Assign filters to allow new TCP connections

Assign arbitrary number of filters that will be applied for each new TCP transport connection on a listening socket. If no filters applied, then TCP transport allows connections from any ip. If at least one filter is applied then new connection source ip should be matched. To clear all filters call zmq_setsockopt(socket, ZMQ_TCP_ACCEPT_FILTER, NULL, 0). Filter is a null-terminated string with ipv6 or ipv4 CIDR.

Option value type	binary data
Option value unit	N/A
Default value	no filters (allow from all)
Applicable socket types	all listening sockets, when using TCP 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);

AUTHORS

This 0MQ manual page was written by Martin Sustrik <sustrik@250bpm.com> and Martin Lucina <mato@kotelna.sk>.