Provided by: libzmq-dev_2.1.11-1ubuntu1_amd64 bug

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.

       Option value type         int

       Option value unit         N/A

       Default value             N/A

       Applicable socket types   all

   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 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 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         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 its 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 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         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 infrastructure (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.

       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         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.

       Option value type         int64_t

       Option value unit         seconds

       Default value             10

       Applicable socket types   all, when using multicast
                                 transports

   ZMQ_RECOVERY_IVL_MSEC: Get multicast recovery interval in milliseconds
       The ZMQ_RECOVERY_IVL’_MSEC option shall retrieve the recovery interval, in milliseconds,
       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.

       For backward compatibility, the default value of ZMQ_RECOVERY_IVL_MSEC is -1 indicating
       that the recovery interval should be obtained from the ZMQ_RECOVERY_IVL option. However,
       if the ZMQ_RECOVERY_IVL_MSEC value is not zero, then it will take precedence, and be used.

       Option value type         int64_t

       Option value unit         milliseconds

       Default value             -1

       Applicable socket types   all, when using multicast
                                 transports

   ZMQ_MCAST_LOOP: Control multicast loop-back
       The ZMQ_MCAST_LOOP option controls whether data sent via multicast transports can also be
       received by the sending host via loop-back. A value of zero indicates that the loop-back
       functionality is disabled, while the default value of 1 indicates that the loop-back
       functionality is enabled. Leaving multicast loop-back 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         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.

       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

   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 zmq_close(3), and further affects the
       termination of the socket’s context with 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.

           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.

       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.

       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.

       Option value type         int

       Option value unit         connections

       Default value             100

       Applicable socket types   all, only for
                                 connection-oriented 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.

       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.

       Option value type         uint32_t

       Option value unit         N/A (flags)

       Default value             N/A

       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.

       ENOTSOCK
           The provided socket was invalid.

       EINTR
           The operation was interrupted by delivery of a signal.

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

       zmq_setsockopt(3) zmq_socket(3) zmq(7)

AUTHORS

       This 0MQ manual page 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