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_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 ALSO¶
zmq_setsockopt(3) zmq_socket(3) zmq(7)
AUTHORS¶
This manual page was written by the 0MQ community.