ZMQ_GETSOCKOPT(3)                 0MQ Manual                 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.


       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 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 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:

       o   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.

       o   The value of 0 specifies no linger period. Pending messages shall
           be discarded immediately when the socket is closed with
           zmq_close().

       o   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



0MQ 2.1.6                         05/07/2011                 ZMQ_GETSOCKOPT(3)
