zmq_getsockopt(3)

SYNOPSIS

int zmq_getsockopt (void *socket, int option_name, void *option_value, size_t *option_len);

DESCRIPTION

The zmq_getsockopt() function shall retrieve the value for the option +specified by the option_name argument for the ØMQ socket pointed to by the +socket argument, and store it in the buffer pointed to by the option_value +argument. The option_len argument is the size in bytes of the buffer pointed +to by option_value; upon successful completion zmq_getsockopt() shall +modify the option_value argument to indicate the actual size of the option +value stored in the buffer.

The following options can be retrieved with the zmq_getsockopt() function:

ZMQ_RCVMORE: More message parts to follow

The ZMQ_RCVMORE option shall return a boolean value indicating if the +multi-part message currently being read from the specified socket has more +message parts to follow. If there are no message parts to follow or if the +message currently being read is not a multi-part message a value of zero shall +be returned. Otherwise, a value of 1 shall be returned.

Refer to zmq_send(3) and zmq_recv(3) for a detailed description +of sending/receiving multi-part messages.

+ + + + + + + + + + + + + + + + +

+Option value type + +	+ +int64_t + +
+Option value unit + +	+ +boolean + +
+Default value + +	+ +N/A + +
+Applicable socket types + +	+ +all + +

ZMQ_HWM: Retrieve high water mark

The ZMQ_HWM option shall retrieve 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: Retrieve disk offload size

The ZMQ_SWAP option shall retrieve 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: Retrieve I/O thread affinity

The ZMQ_AFFINITY option shall retrieve 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: Retrieve socket identity

The ZMQ_IDENTITY option shall retrieve 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 can 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_RATE: Retrieve multicast data rate

The ZMQ_RATE option shall retrieve the maximum send or receive data rate for +multicast transports 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: Get multicast recovery interval

The ZMQ_RECOVERY_IVL option shall retrieve 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.

+ + + + + + + + + + + + + + + + +

+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 controls whether data sent via multicast +transports can also be received by the sending host via loopback. A value of +zero indicates that the loopback functionality is disabled, while the default +value of 1 indicates that the loopback functionality is enabled. 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: Retrieve kernel transmit buffer size

The ZMQ_SNDBUF option shall retrieve the underlying kernel transmit buffer +size for the specified socket. A value of zero means that the OS default is +in effect. For details 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: Retrieve kernel receive buffer size

The ZMQ_RCVBUF option shall retrieve the underlying kernel receive buffer +size for the specified socket. A value of zero means that the OS default is +in effect. 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_getsockopt() 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, or the size of the buffer pointed to by +option_value, as specified by option_len, is insufficient for storing the +option value. +
+
+ETERM +: +
+The ØMQ context associated with the specified socket was terminated. +
+

EXAMPLE

Retrieving the high water mark

/* Retrieve high water mark into hwm */
+int64_t hwm;
+rc = zmq_getsockopt (socket, ZMQ_HWM, &hwm, sizeof hwm);
+assert (rc == 0);

AUTHORS

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

+zmq_getsockopt(3) Manual Page +

NAME

SYNOPSIS

DESCRIPTION

ZMQ_RCVMORE: More message parts to follow

ZMQ_HWM: Retrieve high water mark

ZMQ_SWAP: Retrieve disk offload size

ZMQ_AFFINITY: Retrieve I/O thread affinity

ZMQ_IDENTITY: Retrieve socket identity

ZMQ_RATE: Retrieve multicast data rate

ZMQ_RECOVERY_IVL: Get multicast recovery interval

ZMQ_MCAST_LOOP: Control multicast loopback

ZMQ_SNDBUF: Retrieve kernel transmit buffer size

ZMQ_RCVBUF: Retrieve kernel receive buffer size

RETURN VALUE

ERRORS

EXAMPLE

SEE ALSO

AUTHORS