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 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_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(3) for details on the exact action taken for each socket type.
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.

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.
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(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_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. Socket identity is used only by request/reply pattern. Namely, it can be used in tandem with ROUTER socket to route messages to the peer with specific identity.

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_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 | 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(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.

  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.

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

The 0MQ documentation was written by Martin Sustrik <sustrik@250bpm.com[1]> and Martin Lucina <martin@lucina.net[2]>.

NOTES

1.  sustrik@250bpm.com
    mailto:sustrik@250bpm.com

2.  martin@lucina.net
    mailto:martin@lucina.net