ZMQ_GETSOCKOPT(3) 0MQ Manual ZMQ_GETSOCKOPT(3)NAMEzmq_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 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 zmq_send(3) and zmq_recv(3) for a detailed description of
multi-part messages.
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. A
value of zero means no limit.
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.
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. A
value of zero means no limit.
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.
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 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 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.
Option value type binary data
Option value unit N/A
Default value NULL
Applicable socket types ZMQ_REP, ZMQ_REQ,
ZMQ_ROUTER, ZMQ_DEALER.
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 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.
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.
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.
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 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. The value -1 means no
reconnection.
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_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.
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.
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.
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.
Option value type int
Option value unit milliseconds
Default value -1 (infinite)
Applicable socket types all
ZMQ_IPV6: Retrieve IPv6 socket status
Retrieve the IPv6 option for the socket. A value of 1 means IPv6 is
enabled on the socket, while 0 means the socket will use only IPv4.
When IPv6 is enabled the socket will connect to, or accept connections
from, both IPv4 and IPv6 hosts.
Option value type int
Option value unit boolean
Default value 0 (false)
Applicable socket types all, when using TCP
transports.
ZMQ_IPV4ONLY: Retrieve IPv4-only socket override status
Retrieve the IPv4-only option for the socket. This option is
deprecated. Please use the ZMQ_IPV6 option.
Option value type int
Option value unit boolean
Default value 1 (true)
Applicable socket types all, when using TCP
transports.
ZMQ_IMMEDIATE: Retrieve attach-on-connect value
Retrieve the state of the attach on connect value. If set to 1, will
delay the attachment of a pipe on connect until the underlying
connection has completed. This will cause the socket to block if there
are no other connections, but will prevent queues from filling on pipes
awaiting connection.
Option value type int
Option value unit boolean
Default value 0 (false)
Applicable socket types all, primarily when using
TCP/IPC 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.
Note
The returned file descriptor is also used internally by the
zmq_send and zmq_recv functions. As the descriptor is edge
triggered, applications must update the state of ZMQ_EVENTS after
each invocation of zmq_send or zmq_recv.To be more explicit: after
calling zmq_send the socket may become readable (and vice versa)
without triggering a read event on the file descriptor.
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 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).
Option value type NULL-terminated character
string
Option value unit N/A
Default value NULL
Applicable socket types all, when binding TCP or
IPC transports
ZMQ_TCP_KEEPALIVE: Override SO_KEEPALIVE socket option
Override SO_KEEPALIVE socket option(where supported by OS). The default
value of -1 means to skip any overrides and leave it to OS default.
Option value type int
Option value unit -1,0,1
Default value -1 (leave to OS default)
Applicable socket types all, when using TCP
transports.
ZMQ_TCP_KEEPALIVE_IDLE: Override TCP_KEEPCNT(or TCP_KEEPALIVE on some OS)
Override TCP_KEEPCNT(or TCP_KEEPALIVE on some OS) socket option (where
supported by OS). The default value of -1 means to skip any overrides
and leave it to OS default.
Option value type int
Option value unit -1,>0
Default value -1 (leave to OS default)
Applicable socket types all, when using TCP
transports.
ZMQ_TCP_KEEPALIVE_CNT: Override TCP_KEEPCNT socket option
Override TCP_KEEPCNT socket option(where supported by OS). The default
value of -1 means to skip any overrides and leave it to OS default.
Option value type int
Option value unit -1,>0
Default value -1 (leave to OS default)
Applicable socket types all, when using TCP
transports.
ZMQ_TCP_KEEPALIVE_INTVL: Override TCP_KEEPINTVL socket option
Override TCP_KEEPINTVL socket option(where supported by OS). The
default value of -1 means to skip any overrides and leave it to OS
default.
Option value type int
Option value unit -1,>0
Default value -1 (leave to OS default)
Applicable socket types all, when using TCP
transports.
ZMQ_MECHANISM: Retrieve current security mechanism
The ZMQ_MECHANISM option shall retrieve the current security mechanism
for the socket.
Option value type int
Option value unit ZMQ_NULL, ZMQ_PLAIN, or
ZMQ_CURVE
Default value ZMQ_NULL
Applicable socket types all, when using TCP or IPC
transports
ZMQ_PLAIN_SERVER: Retrieve current PLAIN server role
Returns the ZMQ_PLAIN_SERVER option, if any, previously set on the
socket.
Option value type int
Option value unit 0, 1
Default value int
Applicable socket types all, when using TCP or IPC
transports
ZMQ_PLAIN_USERNAME: Retrieve current PLAIN username
The ZMQ_PLAIN_USERNAME option shall retrieve the last username set for
the PLAIN security mechanism. The returned value shall be a
NULL-terminated string and MAY be empty. The returned size SHALL
include the terminating null byte.
Option value type NULL-terminated character
string
Option value unit N/A
Default value null string
Applicable socket types all, when using TCP or IPC
transports
ZMQ_PLAIN_PASSWORD: Retrieve current password
The ZMQ_PLAIN_PASSWORD option shall retrieve the last password set for
the PLAIN security mechanism. The returned value shall be a
NULL-terminated string and MAY be empty. The returned size SHALL
include the terminating null byte.
Option value type NULL-terminated character
string
Option value unit N/A
Default value null string
Applicable socket types all, when using TCP or IPC
transports
ZMQ_CURVE_PUBLICKEY: Retrieve current CURVE public key
Retrieves the current long term public key for the socket. You can
provide either a 32 byte buffer, to retrieve the binary key value, or a
41 byte buffer, to retrieve the key in a printable Z85 format. NOTE: to
fetch a printable key, the buffer must be 41 bytes large to hold the
40-char key value and one null byte.
Option value type binary data or Z85 text
string
Option value size 32 or 41
Default value null
Applicable socket types all, when using TCP
transport
ZMQ_CURVE_SECRETKEY: Retrieve current CURVE secret key
Retrieves the current long term secret key for the socket. You can
provide either a 32 byte buffer, to retrieve the binary key value, or a
41 byte buffer, to retrieve the key in a printable Z85 format.
Option value type binary data or Z85 text
string
Option value size 32 or 41
Default value null
Applicable socket types all, when using TCP
transport
ZMQ_CURVE_SERVERKEY: Retrieve current CURVE server key
Retrieves the current server key for the client socket. You can provide
either a 32 byte buffer, to retrieve the binary key value, or a 40 byte
buffer, to retrieve the key in a printable Z85 format.
Option value type binary data or Z85 text
string
Option value size 32 or 41
Default value null
Applicable socket types all, when using TCP
transport
ZMQ_ZAP_DOMAIN: Retrieve RFC 27 authentication domain
The ZMQ_ZAP_DOMAIN option shall retrieve the last ZAP domain set for
the socket. The returned value shall be a NULL-terminated string and
MAY be empty. The returned size SHALL include the terminating null
byte.
Option value type character string
Option value unit N/A
Default value not set
Applicable socket types all, when using TCP
transport
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 ALSOzmq_setsockopt(3)zmq_socket(3)zmq(7)AUTHORS
This page was written by the 0MQ community. To make a change please
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0MQ 4.0.1 03/10/2014 ZMQ_GETSOCKOPT(3)
