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.
Note
All 0MQ sockets passed to the zmq_poll() function must share the
same 0MQ context and must belong to the thread calling zmq_poll().
For each zmq_pollitem_t item, zmq_poll() shall first clear the revents
member, and then indicate any requested events that have occured by
setting the bit corresponding to the event condition in the revents
member.
If none of the requested events have occured on any zmq_pollitem_t
item, zmq_poll() shall wait up to timeout microseconds 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 occured
on at least one zmq_pollitem_t.
The events and revents members of zmq_pollitem_t are bitmasks
constructed by OR’ing a combination of the following event flags:
ZMQ_POLLIN
For 0MQ sockets, at least one message may be dequeued from the
underlying message queue associated with 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 queued on the
underlying message queue associated with 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().
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.
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 the timeout period has expired and no events have been signaled.
Upon failure, zmq_poll() shall return -1 and set errno to one of the
values defined below.
ERRORS
EFAULT
At least one of the members of the items array refers to a socket
belonging to a different application thread.
ENOTSUP
At least one of the members of the items array refers to a socket
whose associated 0MQ context was initialised without the ZMQ_POLL
flag.
EXAMPLE
Example 1. 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
The 0MQ documentation 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