zmq_poll(3)

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 ØMQ +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 ØMQ socket referenced by +socket shall take precedence and the value of fd shall be ignored.

+ + + +

Note

All ØMQ sockets passed to the zmq_poll() function must share the +same ØMQ 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 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 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 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 ØMQ 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 ØMQ 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 ØMQ 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 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 ØMQ 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 ØMQ 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 */

AUTHORS

This ØMQ manual page was written by Martin Sustrik <sustrik@250bpm.com> and +Martin Lucina <mato@kotelna.sk>.

+zmq_poll(3) Manual Page +