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 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.
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.
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: Set 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 |
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 |
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_IPV4ONLY: Retrieve IPv4-only socket override status¶
Retrieve the underlying native socket type. A value of 1 will use IPv4 sockets,
while the value of 0 will use IPv6 sockets. An IPv6 socket lets applications
connect to and accept connections from both IPv4 and IPv6 hosts.
Option value type |
int |
Option value unit |
boolean |
Default value |
1 (true) |
Applicable socket types |
all, when using TCP transports. |
ZMQ_DELAY_ATTACH_ON_CONNECT: 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 |
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. |
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 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