zmq_getsockopt(3) ================= NAME ---- zmq_getsockopt - get 0MQ socket options 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 0MQ 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_len' 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 linkzmq:zmq_send[3] and linkzmq:zmq_recv[3] for a detailed description of sending/receiving multi-part messages. [horizontal] 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 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 linkzmq:zmq_socket[3] for details on the exact action taken for each socket type. The default 'ZMQ_HWM' value of zero means "no limit". [horizontal] Option value type:: uint64_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. [horizontal] 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 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 linkzmq:zmq_init[3] for details on allocating the number of I/O threads for a specific _context_. [horizontal] Option value type:: uint64_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 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 can be at least one byte and at most 255 bytes long. Identities starting with binary zero are reserved for use by 0MQ infrastructure. [horizontal] 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'. [horizontal] Option value type:: int64_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. [horizontal] Option value type:: int64_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. [horizontal] Option value type:: int64_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. [horizontal] 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. [horizontal] 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 0MQ 'context' associated with the specified 'socket' was terminated. *EFAULT*:: The provided 'socket' was not valid (NULL). EXAMPLE ------- .Retrieving the high water mark ---- /* Retrieve high water mark into hwm */ int64_t hwm; size_t hwm_size = sizeof (hwm); rc = zmq_getsockopt (socket, ZMQ_HWM, &hwm, &hwm_size); assert (rc == 0); ---- SEE ALSO -------- linkzmq:zmq_setsockopt[3] linkzmq:zmq_socket[3] linkzmq:zmq[7] AUTHORS ------- The 0MQ documentation was written by Martin Sustrik and Martin Lucina .