/* 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);
zmq_setsockopt - set 0MQ socket options
int zmq_setsockopt (void *socket, int option_name, const void *option_value, size_t option_len);
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 options are defined:
The ZMQ_HWM option shall set the high water mark for the message queue associated with the socket. The high water mark is a hard limit on the number of outstanding messages in the queue; if this limit has been reached the socket shall enter an "emergency" state and depending on the socket type, ØMQ shall take appropriate action such as blocking or dropping new messages entering the queue.
The default ZMQ_HWM value of zero means "no limit".
int64_t
messages
0
all
The ZMQ_LWM option shall set the low water mark for the message queue associated with the socket. This option only makes sense when used in conjunction with the ZMQ_HWM option. A socket which has reached it’s high water mark remains in the "emergency" state until the number of outstanding messages in it’s associated message queue falls below the low water mark, at which point normal message processing is resumed.
int64_t
messages
0
all
The ZMQ_SWAP option shall set the disk offload (swap) size for the message queue associated with the 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.
int64_t
bytes
0
all
The ZMQ_AFFINITY option shall set the I/O thread affinity for connections created by subsequent zmq_connect() or zmq_bind() calls on the specified socket.
sockets. 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.
int64_t
N/A (bitmap)
0
N/A
The ZMQ_IDENTITY option shall set the identity of the 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.
binary data
N/A
NULL
all
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.
binary data
N/A
N/A
ZMQ_SUB
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.
binary data
N/A
N/A
ZMQ_SUB
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.
uint64_t
kilobits per second
100
all, when using multicast transports
The ZMQ_RECOVERY_IVL option shall set the recovery interval for multicast transports such as zmq_pgm(7) 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. |
uint64_t
seconds
10
all, when using multicast transports
The ZMQ_MCAST_LOOP option shall control whether data sent via multicast transports 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.
uint64_t
boolean
1
all, when using multicast transports
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.
uint64_t
bytes
0
all
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.
uint64_t
bytes
0
all
The zmq_setsockopt() function shall return zero if successful. Otherwise it shall return -1 and set errno to one of the values defined below.
The requested option option_name is unknown, or the requested option_len or option_value is invalid.
/* 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);
/* Incoming connections on TCP port 5555 shall be handled by I/O thread 1 */ rc = zmq_setsockopt (socket, ZMQ_AFFINITY, 1, sizeof (int64_t)); 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 */ rc = zmq_setsockopt (socket, ZMQ_AFFINITY, 2, sizeof (int64_t)); assert (rc); rc = zmq_bind (socket, "tcp://lo:5555"); assert (rc);
The ØMQ documentation was written by Martin Sustrik <sustrik@250bpm.com> and Martin Lucina <mato@kotelna.sk>.