ZMQ_POLL(3) 0MQ Manual ZMQ_POLL(3)
NAME
zmq_poll - input/output multiplexing
SYNOPSIS
int zmq_poll (zmq_pollitem_t *items, int nitems, long timeout);
DESCRIPTION
The zmq_poll() function provides a mechanism for applications to
multiplex input/output events in a level-triggered fashion over a set
of sockets. Each member of the array pointed to by the items argument
is a zmq_pollitem_t structure. The nitems argument specifies the number
of items in the items array. The zmq_pollitem_t structure is defined as
follows:
typedef struct
{
void *socket;
int fd;
short events;
short revents;
} zmq_pollitem_t;
For each zmq_pollitem_t item, zmq_poll() shall examine either the 0MQ
socket referenced by socket or the standard socket specified by the
file descriptor fd, for the event(s) specified in events. If both
socket and fd are set in a single zmq_pollitem_t, the 0MQ socket
referenced by socket shall take precedence and the value of fd shall be
ignored.
For each zmq_pollitem_t item, zmq_poll() shall first clear the revents
member, and then indicate any requested events that have occurred by
setting the bit corresponding to the event condition in the revents
member.
If none of the requested events have occurred on any zmq_pollitem_t
item, zmq_poll() shall wait timeout milliseconds for an event to occur
on any of the requested items. If the value of timeout is 0, zmq_poll()
shall return immediately. If the value of timeout is -1, zmq_poll()
shall block indefinitely until a requested event has occurred on at
least one zmq_pollitem_t.
The events and revents members of zmq_pollitem_t are bit masks
constructed by OR’ing a combination of the following event flags:
ZMQ_POLLIN
For 0MQ sockets, at least one message may be received from the
socket without blocking. For standard sockets this is equivalent to
the POLLIN flag of the poll() system call and generally means that
at least one byte of data may be read from fd without blocking.
ZMQ_POLLOUT
For 0MQ sockets, at least one message may be sent to the socket
without blocking. For standard sockets this is equivalent to the
POLLOUT flag of the poll() system call and generally means that at
least one byte of data may be written to fd without blocking.
ZMQ_POLLERR
For standard sockets, this flag is passed through zmq_poll() to the
underlying poll() system call and generally means that some sort of
error condition is present on the socket specified by fd. For 0MQ
sockets this flag has no effect if set in events, and shall never
be returned in revents by zmq_poll().
ZMQ_POLLPRI
For 0MQ sockets this flags is of no use. For standard sockets this
means there is urgent data to read. Refer to the POLLPRI flag for
more informations. For file descriptor, refer to your use case: as
an example, GPIO interrupts are signaled through a POLLPRI event.
This flag has no effect on Windows.
Note
The zmq_poll() function may be implemented or emulated using
operating system interfaces other than poll(), and as such may be
subject to the limits of those interfaces in ways not defined in
this documentation.
THREAD SAFETY
The zmq_pollitem_t array must only be used by the thread which will/is
calling zmq_poll.
If a socket is contained in multiple zmq_pollitem_t arrays, each owned
by a different thread, the socket itself needs to be thead-safe
(Server, Client, ...). Otherwise, behaviour is undefined.
RETURN VALUE
Upon successful completion, the zmq_poll() function shall return the
number of zmq_pollitem_t structures with events signaled in revents or
0 if no events have been signaled. Upon failure, zmq_poll() shall
return -1 and set errno to one of the values defined below.
ERRORS
ETERM
At least one of the members of the items array refers to a socket
whose associated 0MQ context was terminated.
EFAULT
The provided items was not valid (NULL).
EINTR
The operation was interrupted by delivery of a signal before any
events were available.
EXAMPLE
Polling indefinitely for input events on both a 0MQ socket and a
standard socket..
zmq_pollitem_t items [2];
/* First item refers to 0MQ socket 'socket' */
items[0].socket = socket;
items[0].events = ZMQ_POLLIN;
/* Second item refers to standard socket 'fd' */
items[1].socket = NULL;
items[1].fd = fd;
items[1].events = ZMQ_POLLIN;
/* Poll for events indefinitely */
int rc = zmq_poll (items, 2, -1);
assert (rc >= 0);
/* Returned events will be stored in items[].revents */
SEE ALSO
zmq_socket(3) zmq_send(3) zmq_recv(3) zmq(7)
Your operating system documentation for the poll() system call.
AUTHORS
This page was written by the 0MQ community. To make a change please
read the 0MQ Contribution Policy at
http://www.zeromq.org/docs:contributing.
0MQ 4.3.4 01/18/2023 ZMQ_POLL(3)
Generated by dwww version 1.15 on Wed Jun 26 18:09:58 CEST 2024.