1ZMQ_POLLER(3) 0MQ Manual ZMQ_POLLER(3)
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6 zmq_poller - input/output multiplexing
7
9 void *zmq_poller_new (void);
10 int zmq_poller_destroy (void *poller_p);
12 int zmq_poller_size (void *poller);
14 int zmq_poller_add (void *poller, void *socket, void *user_data, short
16 events);
17 int zmq_poller_modify (void *poller, void *socket, short events);
19 int zmq_poller_remove (void *poller, void *socket);
21 int zmq_poller_add_fd (void *poller, int fd, void *user_data, short
23 events);
24 int zmq_poller_modify_fd (void *poller, int fd, short events);
26 int zmq_poller_remove_fd (void *poller, int fd);
28 int zmq_poller_wait (void *poller, zmq_poller_event_t *event, long
30 timeout);
31 int zmq_poller_wait_all (void *poller, zmq_poller_event_t *events, int
33 n_events, long timeout);
34 int zmq_poller_fd (void *poller, zmq_fd_t *fd);
36
38 The zmq_poller*_ functions provide a mechanism for applications to
39 multiplex input/output events in a level-triggered fashion over a set
40 of sockets.
41 zmq_poller_new and zmq_poller_destroy manage the lifetime of a poller
43 instance. zmq_poller_new creates and returns a new poller instance,
44 while zmq_poller_destroy destroys it. A pointer to a valid poller must
45 be passed as the poller_p argument of zmq_poller_destroy. In
46 particular, zmq_poller_destroy may not be called multiple times for the
47 same poller instance. zmq_poller_destroy sets the passed pointer to
48 NULL in case of a successful execution. zmq_poller_destroy implicitly
49 unregisters all registered sockets and file descriptors.
50 zmq_poller_size queries the number of sockets or file descriptors
52 registered with a poller. The initial size of a poller is 0, a
53 successful add operation increases the size by 1 and a successful
54 remove operation decreases the size by 1. The size is unaffected by the
55 events specified.
56 zmq_poller_add, zmq_poller_modify and zmq_poller_remove manage the 0MQ
58 sockets registered with a poller.
59 zmq_poller_add registers a new socket with a given poller. Both poller
61 and socket must point to valid 0MQ objects. The events parameter
62 specifies which event types the client wants to subscribe to. It is
63 legal to specify no events (i.e. 0), and activate them later with
64 zmq_poller_modify. In addition, user_data may be specified, which is
65 not used by the poller, but passed back to the caller when an event was
66 signalled in a call to zmq_poller_wait or zmq_poller_wait_all.
67 user_data may be NULL. If it is not NULL, it must be a valid pointer.
68 Otherwise, behaviour is undefined. You must only add a socket to a
69 single poller instance once (unless zmq_poller_remove has been called
70 for that socket before). You may add a socket to multiple poller
71 instances, if the socket itself is explicitly thread-safe (Server,
72 Client, ...). If the socket is not, you may invoke undefined behavior.
73 zmq_poller_modify modifies the subscribed events for a socket. It is
75 legal to specify no events (i.e. 0) to disable events temporarily, and
76 reactivate them later with another call to zmq_poller_modify.
77 zmq_poller_remove removes a socket registration completely.
79 zmq_poller_remove must be called before a socket is closed with
80 zmq_close.
81 Note that it is not necessary to call zmq_poller_remove for any socket
83 before calling zmq_poller_destroy.
84 Also note that calling zmq_poller_remove is not equivalent to calling
86 zmq_poller_modify with no events. zmq_poller_modify does not free
87 resources associated with the socket registration, and requires that
88 the socket remains valid.
89 zmq_poller_add_fd, zmq_poller_modify_fd and zmq_poller_remove_fd are
91 analogous to the previous functions but manage regular file
92 descriptiors registered with a poller. On Windows, these functions can
93 only be used with WinSock sockets.
94 In the following, 0MQ sockets added with zmq_poller_add and file
96 descriptors added with zmq_poller_add_fd are referred to as registered
97 objects.
98 The zmq_poller_event_t structure is defined as follows:
100 typedef struct
102 {
103 void *socket;
104 zmq_fd_t fd;
105 void *user_data;
106 short events;
107 } zmq_poller_event_t;
108 For each registered object, zmq_poller_wait_all() shall examine the
110 registered objects for the event(s) currently registered.
111 If none of the registered events have occurred, zmq_poller_wait_all
113 shall wait timeout milliseconds for an event to occur on any of the
114 registered objects. If the value of timeout is 0, zmq_poller_wait_all
115 shall return immediately. If the value of timeout is -1,
116 zmq_poller_wait_all shall block indefinitely until one event has
117 occurred on any of the registered objects.
118 The events argument zmq_poller_wait_all must be a pointer to an array
120 of at least n_events elements. Behaviour is undefined if events does
121 not point to an array of at least n_events elements.
122 zmq_poller_wait_all returns at most n_events events. If more than
124 n_events events were signalled, only an unspecified subset of the
125 signalled events is returned through events.
126 A caller is advised to ensure that n_events is equal to the number of
128 registered objects. Otherwise, a livelock situation may result: If more
129 than n_events registered objects have an active event on each call to
130 zmq_poller_wait_all, it might happen that the same subset of registered
131 objects is always returned, and the caller never notices the events on
132 the others. The number of objects registered can be queried with
133 zmq_poller_size.
134 zmq_poller_wait_all returns the number of valid elements. The valid
136 elements are placed in positions 0 to n_events - 1 in the events array.
137 All members of a valid element are set to valid values by
138 zmq_poller_wait_all. For socket events socket is non-null and fd is an
139 operating system specific value for an invalid socket (-1 or
140 INVALID_SOCKET). For fd events socket is NULL and fd is a valid file
141 descriptor. The client does therefore not need to initialize the
142 contents of the events array before a call to zmq_poller_wait_all. It
143 is unspecified whether the the remaining elements of events are written
144 to by zmq_poller_wait_all.
145 zmq_poller_fd queries the file descriptor associated with the
147 zmq_poller, and stores it in the address pointer to by fd. The
148 zmq_poller is only guaranteed to have a file descriptor if at least one
149 thread-safe socket is currently registered.
150 Note that closing a socket that is registered in a poller leads to
152 undefined behavior. The socket must be unregistered first.
153
155 The events parameter of zmq_poller_add and zmq_poller_modify, and the
156 events member of the zmq_poller_event_t structure are bit masks
157 constructed by OR’ing a combination of the following event flags:
158 ZMQ_POLLIN
160 For 0MQ sockets, at least one message may be received from the
161 socket without blocking. For standard sockets this is equivalent to
162 the POLLIN flag of the poll() system call and generally means that
163 at least one byte of data may be read from fd without blocking.
164 ZMQ_POLLOUT
166 For 0MQ sockets, at least one message may be sent to the socket
167 without blocking. For standard sockets this is equivalent to the
168 POLLOUT flag of the poll() system call and generally means that at
169 least one byte of data may be written to fd without blocking.
170 ZMQ_POLLERR
172 For 0MQ sockets this flag has no effect on the zmq_poller_add and
173 zmq_poller_modify functions, and is never set in the events member
174 of the zmq_poller_event_t structure. For standard sockets, this
175 flag is passed through zmq_poller_wait_all to the underlying poll()
176 system call and generally means that some sort of error condition
177 is present on the socket specified by fd.
178 ZMQ_POLLPRI
180 For 0MQ sockets this flag has no effect on the zmq_poller_add and
181 zmq_poller_modify functions, and is never set in the events member
182 of the zmq_poller_event_t structure. For standard sockets this
183 means there is urgent data to read. Refer to the POLLPRI flag for
184 more informations. For a file descriptor, refer to your OS
185 documentation: as an example, GPIO interrupts are signaled through
186 a POLLPRI event. This flag has no effect on Windows.
187 Note
189 The zmq_poller*_ functions may be implemented or emulated using
190 operating system interfaces other than poll(), and as such may be
191 subject to the limits of those interfaces in ways not defined in
192 this documentation.
193
195 Like most other 0MQ objects, a poller is not thread-safe. All
196 operations must be called from the same thread. Otherwise, behaviour is
197 undefined.
198 In addition to that, if you want to add a socket to multiple existing
200 poller instances, the socket itself needs to be thread-safe (Server,
201 Client, ...). Otherwise, behaviour is undefined.
202
204 zmq_poller_new returns a valid pointer to a poller, or NULL in case of
205 a failure.
206 All functions that return an int, return -1 in case of a failure. In
208 that case, zmq_errno() can be used to query the type of the error as
209 described below.
210 zmq_poller_wait_all returns the number of events signalled and returned
212 in the events array. It never returns 0.
213 All other functions return 0 in case of a successful execution.
215
217 On zmq_poller_new: ENOMEM:: A new poller could not be allocated
218 successfully.
219 On zmq_poller_destroy: EFAULT:: poller_p did not point to a valid
221 poller. Note that passing an invalid pointer (e.g. pointer to
222 deallocated memory) may cause undefined behaviour (e.g. an access
223 violation).
224 On zmq_poller_size: EFAULT:: poller did not point to a valid poller.
226 Note that passing an invalid pointer (e.g. pointer to deallocated
227 memory) may cause undefined behaviour (e.g. an access violation).
228 On zmq_poller_add, zmq_poller_modify and zmq_poller_remove: EFAULT::
230 poller did not point to a valid poller. Note that passing an invalid
231 pointer (e.g. pointer to deallocated memory) may cause undefined
232 behaviour (e.g. an access violation). ENOTSOCK:: socket did not point
233 to a valid socket. Note that passing an invalid pointer (e.g. pointer
234 to deallocated memory) may cause undefined behaviour (e.g. an access
235 violation).
236 On zmq_poller_add: EMFILE:: TODO
238 On zmq_poller_add or zmq_poller_add_fd: ENOMEM:: Necessary resources
240 could not be allocated. EINVAL:: socket resp. fd was already registered
241 with the poller.
242 On zmq_poller_modify, zmq_poller_modify_fd, zmq_poller_remove or
244 zmq_poller_remove_fd: EINVAL:: socket resp. fd was not registered with
245 the poller.
246 On zmq_poller_add_fd, zmq_poller_modify_fd and zmq_poller_remove_fd:
248 EBADF*: The fd specified was the retired fd.
249 On zmq_poller_wait and zmq_poller_wait_all: ENOMEM:: Necessary
251 resources could not be allocated. ETERM:: At least one of the
252 registered objects is a socket whose associated 0MQ context was
253 terminated. EFAULT:: The provided events was NULL, or poller did not
254 point to a valid poller, or there are no registered objects or all
255 event subscriptions are disabled and timeout was negative. EINTR:: The
256 operation was interrupted by delivery of a signal before any events
257 were available. EAGAIN:: No registered event was signalled before the
258 timeout was reached.
259 On zmq_poller_fd: EINVAL:: The poller has no associated file
261 descriptor. EFAULT:: The provided poller did not point to a valid
262 poller.
263
265 Polling indefinitely for input events on both a 0MQ socket and a
266 standard socket..
267 void *poller = zmq_poller_new ();
269 zmq_poller_event_t events [2];
271 /* First item refers to 0MQ socket 'socket' */
272 zmq_poller_add (poller, socket, NULL, ZMQ_POLLIN);
273 /* Second item refers to standard socket 'fd' */
274 zmq_poller_add_fd (poller, fd, NULL, ZMQ_POLLIN);
275 /* Poll for events indefinitely */
276 int rc = zmq_poller_wait_all (poller, events, 2, -1);
277 assert (rc >= 0);
278 /* Returned events will be stored in 'events' */
279 zmq_poller_destroy (poller);
280
283 zmq_socket(3) zmq_send(3) zmq_recv(3) zmq(7)
284
286 This page was written by the 0MQ community. To make a change please
287 read the 0MQ Contribution Policy at
288 http://www.zeromq.org/docs:contributing.
2890MQ 4.3.4 07/23/2022 ZMQ_POLLER(3)