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 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_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_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 ALSOzmq_setsockopt(3)zmq_socket(3)zmq(7)AUTHORS
This manual page was written by the 0MQ community.
0MQ 2.2.0 04/04/2012 ZMQ_GETSOCKOPT(3)
