1ZMQ_GETSOCKOPT(3) 0MQ Manual ZMQ_GETSOCKOPT(3)
2
6 zmq_getsockopt - get 0MQ socket options
7
9 int zmq_getsockopt (void *socket, int option_name, void *option_value,
10 size_t *option_len);
11
13 The zmq_getsockopt() function shall retrieve the value for the option
14 specified by the option_name argument for the 0MQ socket pointed to by
15 the socket argument, and store it in the buffer pointed to by the
16 option_value argument. The option_len argument is the size in bytes of
17 the buffer pointed to by option_value; upon successful completion
18 zmq_getsockopt() shall modify the option_len argument to indicate the
19 actual size of the option value stored in the buffer.
20 The following options can be retrieved with the zmq_getsockopt()
22 function:
23 ZMQ_TYPE: Retrieve socket type
25 The ZMQ_TYPE option shall retrieve the socket type for the specified
26 socket. The socket type is specified at socket creation time and cannot
27 be modified afterwards.
28 Option value type int
31 Option value unit N/A
33 Default value N/A
35 Applicable socket types all
37 ZMQ_RCVMORE: More message parts to follow
40 The ZMQ_RCVMORE option shall return a boolean value indicating if the
41 multi-part message currently being read from the specified socket has
42 more message parts to follow. If there are no message parts to follow
43 or if the message currently being read is not a multi-part message a
44 value of zero shall be returned. Otherwise, a value of 1 shall be
45 returned.
46 Refer to zmq_send(3) and zmq_recv(3) for a detailed description of
48 sending/receiving multi-part messages.
49 Option value type int64_t
52 Option value unit boolean
54 Default value N/A
56 Applicable socket types all
58 ZMQ_HWM: Retrieve high water mark
61 The ZMQ_HWM option shall retrieve the high water mark for the specified
62 socket. The high water mark is a hard limit on the maximum number of
63 outstanding messages 0MQ shall queue in memory for any single peer that
64 the specified socket is communicating with.
65 If this limit has been reached the socket shall enter an exceptional
67 state and depending on the socket type, 0MQ shall take appropriate
68 action such as blocking or dropping sent messages. Refer to the
69 individual socket descriptions in zmq_socket(3) for details on the
70 exact action taken for each socket type.
71 The default ZMQ_HWM value of zero means "no limit".
73 Option value type uint64_t
76 Option value unit messages
78 Default value 0
80 Applicable socket types all
82 ZMQ_SWAP: Retrieve disk offload size
85 The ZMQ_SWAP option shall retrieve the disk offload (swap) size for the
86 specified socket. A socket which has ZMQ_SWAP set to a non-zero value
87 may exceed it’s high water mark; in this case outstanding messages
88 shall be offloaded to storage on disk rather than held in memory.
89 The value of ZMQ_SWAP defines the maximum size of the swap space in
91 bytes.
92 Option value type int64_t
95 Option value unit bytes
97 Default value 0
99 Applicable socket types all
101 ZMQ_AFFINITY: Retrieve I/O thread affinity
104 The ZMQ_AFFINITY option shall retrieve the I/O thread affinity for
105 newly created connections on the specified socket.
106 Affinity determines which threads from the 0MQ I/O thread pool
108 associated with the socket’s context shall handle newly created
109 connections. A value of zero specifies no affinity, meaning that work
110 shall be distributed fairly among all 0MQ I/O threads in the thread
111 pool. For non-zero values, the lowest bit corresponds to thread 1,
112 second lowest bit to thread 2 and so on. For example, a value of 3
113 specifies that subsequent connections on socket shall be handled
114 exclusively by I/O threads 1 and 2.
115 See also zmq_init(3) for details on allocating the number of I/O
117 threads for a specific context.
118 Option value type uint64_t
121 Option value unit N/A (bitmap)
123 Default value 0
125 Applicable socket types N/A
127 ZMQ_IDENTITY: Retrieve socket identity
130 The ZMQ_IDENTITY option shall retrieve the identity of the specified
131 socket. Socket identity determines if existing 0MQ infrastructure
132 (message queues, forwarding devices) shall be identified with a
133 specific application and persist across multiple runs of the
134 application.
135 If the socket has no identity, each run of an application is completely
137 separate from other runs. However, with identity set the socket shall
138 re-use any existing 0MQ infrastructure configured by the previous
139 run(s). Thus the application may receive messages that were sent in the
140 meantime, message queue limits shall be shared with previous run(s) and
141 so on.
142 Identity can be at least one byte and at most 255 bytes long.
144 Identities starting with binary zero are reserved for use by 0MQ
145 infrastructure.
146 Option value type binary data
149 Option value unit N/A
151 Default value NULL
153 Applicable socket types all
155 ZMQ_RATE: Retrieve multicast data rate
158 The ZMQ_RATE option shall retrieve the maximum send or receive data
159 rate for multicast transports using the specified socket.
160 Option value type int64_t
163 Option value unit kilobits per second
165 Default value 100
167 Applicable socket types all, when using multicast
169 transports
170 ZMQ_RECOVERY_IVL: Get multicast recovery interval
173 The ZMQ_RECOVERY_IVL option shall retrieve the recovery interval for
174 multicast transports using the specified socket. The recovery interval
175 determines the maximum time in seconds that a receiver can be absent
176 from a multicast group before unrecoverable data loss will occur.
177 Option value type int64_t
180 Option value unit seconds
182 Default value 10
184 Applicable socket types all, when using multicast
186 transports
187 ZMQ_RECOVERY_IVL_MSEC: Get multicast recovery interval in milliseconds
190 The ZMQ_RECOVERY_IVL’_MSEC option shall retrieve the recovery interval,
191 in milliseconds, for multicast transports using the specified 'socket.
192 The recovery interval determines the maximum time in seconds that a
193 receiver can be absent from a multicast group before unrecoverable data
194 loss will occur.
195 For backward compatibility, the default value of ZMQ_RECOVERY_IVL_MSEC
197 is -1 indicating that the recovery interval should be obtained from the
198 ZMQ_RECOVERY_IVL option. However, if the ZMQ_RECOVERY_IVL_MSEC value is
199 not zero, then it will take precedence, and be used.
200 Option value type int64_t
203 Option value unit milliseconds
205 Default value -1
207 Applicable socket types all, when using multicast
209 transports
210 ZMQ_MCAST_LOOP: Control multicast loop-back
213 The ZMQ_MCAST_LOOP option controls whether data sent via multicast
214 transports can also be received by the sending host via loop-back. A
215 value of zero indicates that the loop-back functionality is disabled,
216 while the default value of 1 indicates that the loop-back functionality
217 is enabled. Leaving multicast loop-back enabled when it is not required
218 can have a negative impact on performance. Where possible, disable
219 ZMQ_MCAST_LOOP in production environments.
220 Option value type int64_t
223 Option value unit boolean
225 Default value 1
227 Applicable socket types all, when using multicast
229 transports
230 ZMQ_SNDBUF: Retrieve kernel transmit buffer size
233 The ZMQ_SNDBUF option shall retrieve the underlying kernel transmit
234 buffer size for the specified socket. A value of zero means that the OS
235 default is in effect. For details refer to your operating system
236 documentation for the SO_SNDBUF socket option.
237 Option value type uint64_t
240 Option value unit bytes
242 Default value 0
244 Applicable socket types all
246 ZMQ_RCVBUF: Retrieve kernel receive buffer size
249 The ZMQ_RCVBUF option shall retrieve the underlying kernel receive
250 buffer size for the specified socket. A value of zero means that the OS
251 default is in effect. For details refer to your operating system
252 documentation for the SO_RCVBUF socket option.
253 Option value type uint64_t
256 Option value unit bytes
258 Default value 0
260 Applicable socket types all
262 ZMQ_LINGER: Retrieve linger period for socket shutdown
265 The ZMQ_LINGER option shall retrieve the linger period for the
266 specified socket. The linger period determines how long pending
267 messages which have yet to be sent to a peer shall linger in memory
268 after a socket is closed with zmq_close(3), and further affects the
269 termination of the socket’s context with zmq_term(3). The following
270 outlines the different behaviours:
271 · The default value of -1 specifies an infinite linger period.
273 Pending messages shall not be discarded after a call to
274 zmq_close(); attempting to terminate the socket’s context with
275 zmq_term() shall block until all pending messages have been sent to
276 a peer.
277 · The value of 0 specifies no linger period. Pending messages shall
279 be discarded immediately when the socket is closed with
280 zmq_close().
281 · Positive values specify an upper bound for the linger period in
283 milliseconds. Pending messages shall not be discarded after a call
284 to zmq_close(); attempting to terminate the socket’s context with
285 zmq_term() shall block until either all pending messages have been
286 sent to a peer, or the linger period expires, after which any
287 pending messages shall be discarded.
288 Option value type int
290 Option value unit milliseconds
291 Default value -1 (infinite)
292 Applicable socket types all
293 ZMQ_RECONNECT_IVL: Retrieve reconnection interval
296 The ZMQ_RECONNECT_IVL option shall retrieve the initial reconnection
297 interval for the specified socket. The reconnection interval is the
298 period 0MQ shall wait between attempts to reconnect disconnected peers
299 when using connection-oriented transports.
300 Note
302 The reconnection interval may be randomized by 0MQ to prevent
303 reconnection storms in topologies with a large number of peers per
304 socket.
305 Option value type int
308 Option value unit milliseconds
310 Default value 100
312 Applicable socket types all, only for
314 connection-oriented
315 transports
316 ZMQ_RECONNECT_IVL_MAX: Retrieve maximum reconnection interval
319 The ZMQ_RECONNECT_IVL_MAX option shall retrieve the maximum
320 reconnection interval for the specified socket. This is the maximum
321 period 0MQ shall wait between attempts to reconnect. On each reconnect
322 attempt, the previous interval shall be doubled untill
323 ZMQ_RECONNECT_IVL_MAX is reached. This allows for exponential backoff
324 strategy. Default value means no exponential backoff is performed and
325 reconnect interval calculations are only based on ZMQ_RECONNECT_IVL.
326 Note
328 Values less than ZMQ_RECONNECT_IVL will be ignored.
329 Option value type int
332 Option value unit milliseconds
334 Default value 0 (only use
337 ZMQ_RECONNECT_IVL)
338 Applicable socket types all, only for
340 connection-oriented
341 transport
342 ZMQ_BACKLOG: Retrieve maximum length of the queue of outstanding
345 connections
346 The ZMQ_BACKLOG option shall retrieve the maximum length of the queue
347 of outstanding peer connections for the specified socket; this only
348 applies to connection-oriented transports. For details refer to your
349 operating system documentation for the listen function.
350 Option value type int
353 Option value unit connections
355 Default value 100
357 Applicable socket types all, only for
359 connection-oriented
360 transports
361 ZMQ_FD: Retrieve file descriptor associated with the socket
364 The ZMQ_FD option shall retrieve the file descriptor associated with
365 the specified socket. The returned file descriptor can be used to
366 integrate the socket into an existing event loop; the 0MQ library shall
367 signal any pending events on the socket in an edge-triggered fashion by
368 making the file descriptor become ready for reading.
369 Note
371 The ability to read from the returned file descriptor does not
372 necessarily indicate that messages are available to be read from,
373 or can be written to, the underlying socket; applications must
374 retrieve the actual event state with a subsequent retrieval of the
375 ZMQ_EVENTS option.
376 Caution
378 The returned file descriptor is intended for use with a poll or
379 similar system call only. Applications must never attempt to read
380 or write data to it directly, neither should they try to close it.
381 Option value type int on POSIX systems,
384 SOCKET on Windows
385 Option value unit N/A
387 Default value N/A
389 Applicable socket types all
391 ZMQ_EVENTS: Retrieve socket event state
394 The ZMQ_EVENTS option shall retrieve the event state for the specified
395 socket. The returned value is a bit mask constructed by OR’ing a
396 combination of the following event flags:
397 ZMQ_POLLIN
399 Indicates that at least one message may be received from the
400 specified socket without blocking.
401 ZMQ_POLLOUT
403 Indicates that at least one message may be sent to the specified
404 socket without blocking.
405 The combination of a file descriptor returned by the ZMQ_FD option
407 being ready for reading but no actual events returned by a subsequent
408 retrieval of the ZMQ_EVENTS option is valid; applications should simply
409 ignore this case and restart their polling operation/event loop.
410 Option value type uint32_t
413 Option value unit N/A (flags)
415 Default value N/A
417 Applicable socket types all
419
422 The zmq_getsockopt() function shall return zero if successful.
423 Otherwise it shall return -1 and set errno to one of the values defined
424 below.
425
427 EINVAL
428 The requested option option_name is unknown, or the requested
429 option_len or option_value is invalid, or the size of the buffer
430 pointed to by option_value, as specified by option_len, is
431 insufficient for storing the option value.
432 ETERM
434 The 0MQ context associated with the specified socket was
435 terminated.
436 EFAULT
438 The provided socket was not valid (NULL).
439 EINTR
441 The operation was interrupted by delivery of a signal.
442
444 Retrieving the high water mark.
445 /* Retrieve high water mark into hwm */
447 int64_t hwm;
448 size_t hwm_size = sizeof (hwm);
449 rc = zmq_getsockopt (socket, ZMQ_HWM, &hwm, &hwm_size);
450 assert (rc == 0);
451
454 zmq_setsockopt(3) zmq_socket(3) zmq(7)
455
457 This 0MQ manual page was written by Martin Sustrik
458 <sustrik@250bpm.com[1]> and Martin Lucina <mato@kotelna.sk[2]>.
459
461 1. sustrik@250bpm.com
462 mailto:sustrik@250bpm.com
463 2. mato@kotelna.sk
465 mailto:mato@kotelna.sk
4660MQ 2.1.4 03/30/2011 ZMQ_GETSOCKOPT(3)