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 options are defined:
ZMQ_HWM: Set high water mark
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, 0MQ shall take appropriate action such as blocking or
dropping new messages entering the queue.
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_LWM: Set low water mark
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.
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
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.
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
connections created by subsequent zmq_connect() or zmq_bind() calls on
the specified socket.
sockets. 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 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 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.
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 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.
EXAMPLE
Example 1. 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);
Example 2. Setting I/O thread affinity
/* 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);
SEE ALSO
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