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_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 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 + +	+ +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 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 + +	+ +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 ØMQ 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 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 + +	+ +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 ØMQ shall +wait between attempts to reconnect disconnected peers when using +connection-oriented transports.

+ + + +

Note

The reconnection interval may be randomized by ØMQ 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 ØMQ 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 ØMQ 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 ØMQ context associated with the specified socket was terminated. +
+
+EFAULT +: +
+The provided socket was not valid (NULL). +
+
+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);

AUTHORS

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

+zmq_getsockopt(3) Manual Page +

NAME

SYNOPSIS

DESCRIPTION

ZMQ_TYPE: Retrieve socket type

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_RECOVERY_IVL_MSEC: Get multicast recovery interval in milliseconds

ZMQ_MCAST_LOOP: Control multicast loop-back

ZMQ_SNDBUF: Retrieve kernel transmit buffer size

ZMQ_RCVBUF: Retrieve kernel receive buffer size

ZMQ_LINGER: Retrieve linger period for socket shutdown

ZMQ_RECONNECT_IVL: Retrieve reconnection interval

ZMQ_RECONNECT_IVL_MAX: Retrieve maximum reconnection interval

ZMQ_BACKLOG: Retrieve maximum length of the queue of outstanding connections

ZMQ_FD: Retrieve file descriptor associated with the socket

ZMQ_EVENTS: Retrieve socket event state

RETURN VALUE

ERRORS

EXAMPLE

SEE ALSO

AUTHORS