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 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 resolution of timeout is 1
       millisecond.

       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().

           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 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 manual page was written by the 0MQ community.