1ZMQ_POLL(3) 0MQ Manual ZMQ_POLL(3)
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6 zmq_poll - input/output multiplexing
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9 int zmq_poll (zmq_pollitem_t *items, int nitems, long timeout);
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12 The zmq_poll() function provides a mechanism for applications to
13 multiplex input/output events in a level-triggered fashion over a set
14 of sockets. Each member of the array pointed to by the items argument
15 is a zmq_pollitem_t structure. The nitems argument specifies the number
16 of items in the items array. The zmq_pollitem_t structure is defined as
17 follows:
18 typedef struct
20 {
21 void *socket;
22 int fd;
23 short events;
24 short revents;
25 } zmq_pollitem_t;
26 For each zmq_pollitem_t item, zmq_poll() shall examine either the 0MQ
28 socket referenced by socket or the standard socket specified by the
29 file descriptor fd, for the event(s) specified in events. If both
30 socket and fd are set in a single zmq_pollitem_t, the 0MQ socket
31 referenced by socket shall take precedence and the value of fd shall be
32 ignored.
33 For each zmq_pollitem_t item, zmq_poll() shall first clear the revents
35 member, and then indicate any requested events that have occurred by
36 setting the bit corresponding to the event condition in the revents
37 member.
38 If none of the requested events have occurred on any zmq_pollitem_t
40 item, zmq_poll() shall wait timeout milliseconds for an event to occur
41 on any of the requested items. If the value of timeout is 0, zmq_poll()
42 shall return immediately. If the value of timeout is -1, zmq_poll()
43 shall block indefinitely until a requested event has occurred on at
44 least one zmq_pollitem_t.
45 The events and revents members of zmq_pollitem_t are bit masks
47 constructed by OR’ing a combination of the following event flags:
48 ZMQ_POLLIN
50 For 0MQ sockets, at least one message may be received from the
51 socket without blocking. For standard sockets this is equivalent to
52 the POLLIN flag of the poll() system call and generally means that
53 at least one byte of data may be read from fd without blocking.
54 ZMQ_POLLOUT
56 For 0MQ sockets, at least one message may be sent to the socket
57 without blocking. For standard sockets this is equivalent to the
58 POLLOUT flag of the poll() system call and generally means that at
59 least one byte of data may be written to fd without blocking.
60 ZMQ_POLLERR
62 For standard sockets, this flag is passed through zmq_poll() to the
63 underlying poll() system call and generally means that some sort of
64 error condition is present on the socket specified by fd. For 0MQ
65 sockets this flag has no effect if set in events, and shall never
66 be returned in revents by zmq_poll().
67 ZMQ_POLLPRI
69 For 0MQ sockets this flags is of no use. For standard sockets this
70 means there is urgent data to read. Refer to the POLLPRI flag for
71 more informations. For file descriptor, refer to your use case: as
72 an example, GPIO interrupts are signaled through a POLLPRI event.
73 This flag has no effect on Windows.
74 Note
76 The zmq_poll() function may be implemented or emulated using
77 operating system interfaces other than poll(), and as such may be
78 subject to the limits of those interfaces in ways not defined in
79 this documentation.
80
82 The zmq_pollitem_t array must only be used by the thread which will/is
83 calling zmq_poll.
84 If a socket is contained in multiple zmq_pollitem_t arrays, each owned
86 by a different thread, the socket itself needs to be thead-safe
87 (Server, Client, ...). Otherwise, behaviour is undefined.
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90 Upon successful completion, the zmq_poll() function shall return the
91 number of zmq_pollitem_t structures with events signaled in revents or
92 0 if no events have been signaled. Upon failure, zmq_poll() shall
93 return -1 and set errno to one of the values defined below.
94
96 ETERM
97 At least one of the members of the items array refers to a socket
98 whose associated 0MQ context was terminated.
99 EFAULT
101 The provided items was not valid (NULL).
102 EINTR
104 The operation was interrupted by delivery of a signal before any
105 events were available.
106
108 Polling indefinitely for input events on both a 0MQ socket and a
109 standard socket..
110 zmq_pollitem_t items [2];
112 /* First item refers to 0MQ socket 'socket' */
113 items[0].socket = socket;
114 items[0].events = ZMQ_POLLIN;
115 /* Second item refers to standard socket 'fd' */
116 items[1].socket = NULL;
117 items[1].fd = fd;
118 items[1].events = ZMQ_POLLIN;
119 /* Poll for events indefinitely */
120 int rc = zmq_poll (items, 2, -1);
121 assert (rc >= 0);
122 /* Returned events will be stored in items[].revents */
123
126 zmq_socket(3) zmq_send(3) zmq_recv(3) zmq(7)
127 Your operating system documentation for the poll() system call.
129
131 This page was written by the 0MQ community. To make a change please
132 read the 0MQ Contribution Policy at
133 http://www.zeromq.org/docs:contributing.
1340MQ 4.3.4 01/22/2022 ZMQ_POLL(3)