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_TYPE: Retrieve socket type ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The 'ZMQ_TYPE' option shall retrieve the socket type for the specified 'socket'. The socket type is specified at socket creation time and cannot be modified afterwards. [horizontal] Option value type:: int Option value unit:: N/A Default value:: N/A Applicable socket types:: all ZMQ_RCVMORE: More message data parts to follow ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The 'ZMQ_RCVMORE' option shall return True (1) if the message part last received from the 'socket' was a data part with more parts to follow. If there are no data parts to follow, this option shall return False (0). Refer to linkzmq:zmq_send[3] and linkzmq:zmq_recv[3] for a detailed description of multi-part messages. [horizontal] Option value type:: int Option value unit:: boolean Default value:: N/A Applicable socket types:: all ZMQ_SNDHWM: Retrieves high water mark for outbound messages ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The 'ZMQ_SNDHWM' option shall return 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 linkzmq:zmq_socket[3] for details on the exact action taken for each socket type. [horizontal] Option value type:: int Option value unit:: messages Default value:: 1000 Applicable socket types:: all ZMQ_RCVHWM: Retrieve high water mark for inbound messages ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The 'ZMQ_RCVHWM' option shall return 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 linkzmq:zmq_socket[3] for details on the exact action taken for each socket type. [horizontal] Option value type:: int Option value unit:: messages Default value:: 1000 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: Set socket identity ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The 'ZMQ_IDENTITY' option shall retrieve 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. [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:: int 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 milliseconds that a receiver can be absent from a multicast group before unrecoverable data loss will occur. [horizontal] Option value type:: int Option value unit:: milliseconds Default value:: 10000 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:: int 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:: int Option value unit:: bytes Default value:: 0 Applicable socket types:: all ZMQ_LINGER: Retrieve linger period for socket shutdown ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The 'ZMQ_LINGER' option shall retrieve 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 linkzmq:zmq_close[3], and further affects the termination of the socket's context with linkzmq: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. [horizontal] Option value type:: int Option value unit:: milliseconds Default value:: -1 (infinite) Applicable socket types:: all ZMQ_RECONNECT_IVL: Retrieve reconnection interval ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The 'ZMQ_RECONNECT_IVL' option shall retrieve 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. [horizontal] Option value type:: int Option value unit:: milliseconds Default value:: 100 Applicable socket types:: all, only for connection-oriented transports ZMQ_RECONNECT_IVL_MAX: Retrieve maximum reconnection interval ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The 'ZMQ_RECONNECT_IVL_MAX' option shall retrieve 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. [horizontal] Option value type:: int Option value unit:: milliseconds Default value:: 0 (only use ZMQ_RECONNECT_IVL) Applicable socket types:: all, only for connection-oriented transport ZMQ_BACKLOG: Retrieve maximum length of the queue of outstanding connections ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The 'ZMQ_BACKLOG' option shall retrieve 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. [horizontal] 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 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The option shall retrieve limit for the inbound messages. If a peer sends a message larger than ZMQ_MAXMSGSIZE it is disconnected. Value of -1 means 'no limit'. [horizontal] 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 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The option shall retrieve time-to-live used for outbound multicast packets. The default of 1 means that the multicast packets don't leave the local network. [horizontal] 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 socket operation returns with EAGAIN ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Retrieve the timeout for recv 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. [horizontal] Option value type:: int Option value unit:: milliseconds Default value:: -1 (infinite) Applicable socket types:: all ZMQ_SNDTIMEO: Maximum time before a socket operation returns with EAGAIN ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Retrieve 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. [horizontal] Option value type:: int Option value unit:: milliseconds Default value:: -1 (infinite) Applicable socket types:: all ZMQ_IPV4ONLY: Retrieve IPv4-only socket override status ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Retrieve 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. [horizontal] Option value type:: int Option value unit:: boolean Default value:: 1 (true) Applicable socket types:: all, when using TCP transports. ZMQ_FD: Retrieve file descriptor associated with the socket ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The 'ZMQ_FD' option shall retrieve the file descriptor associated with the specified 'socket'. The returned file descriptor can be used to integrate the socket into an existing event loop; the 0MQ library shall signal any pending events on the socket in an _edge-triggered_ fashion by making the file descriptor become ready for reading. NOTE: The ability to read from the returned file descriptor does not necessarily indicate that messages are available to be read from, or can be written to, the underlying socket; applications must retrieve the actual event state with a subsequent retrieval of the 'ZMQ_EVENTS' option. CAUTION: The returned file descriptor is intended for use with a 'poll' or similar system call only. Applications must never attempt to read or write data to it directly, neither should they try to close it. [horizontal] Option value type:: int on POSIX systems, SOCKET on Windows Option value unit:: N/A Default value:: N/A Applicable socket types:: all ZMQ_EVENTS: Retrieve socket event state ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The 'ZMQ_EVENTS' option shall retrieve the event state for the specified 'socket'. The returned value is a bit mask constructed by OR'ing a combination of the following event flags: *ZMQ_POLLIN*:: Indicates that at least one message may be received from the specified socket without blocking. *ZMQ_POLLOUT*:: Indicates that at least one message may be sent to the specified socket without blocking. The combination of a file descriptor returned by the 'ZMQ_FD' option being ready for reading but no actual events returned by a subsequent retrieval of the 'ZMQ_EVENTS' option is valid; applications should simply ignore this case and restart their polling operation/event loop. [horizontal] Option value type:: int Option value unit:: N/A (flags) Default value:: N/A Applicable socket types:: all ZMQ_LAST_ENDPOINT: Retrieve the last endpoint set ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The 'ZMQ_LAST_ENDPOINT' option shall retrieve the last endpoint bound for TCP and IPC transports. The returned value will be a string in the form of a ZMQ DSN. Note that if the TCP host is INADDR_ANY, indicated by a *, then the returned address will be 0.0.0.0 (for IPv4). [horizontal] Option value type:: character string Option value unit:: N/A Default value:: NULL Applicable socket types:: all, when binding TCP or IPC transports 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. *ENOTSOCK*:: The provided 'socket' was invalid. *EINTR*:: The operation was interrupted by delivery of a signal. EXAMPLE ------- .Retrieving the high water mark for outgoing messages ---- /* Retrieve high water mark into sndhwm */ int sndhwm; size_t sndhwm_size = sizeof (sndhwm); rc = zmq_getsockopt (socket, ZMQ_SNDHWM, &sndhwm, &sndhwm_size); assert (rc == 0); ---- SEE ALSO -------- linkzmq:zmq_setsockopt[3] linkzmq:zmq_socket[3] linkzmq:zmq[7] AUTHORS ------- This 0MQ manual page was written by Martin Sustrik and Martin Lucina .