NAME

       xs_poll - input/output multiplexing

SYNOPSIS

       int xs_poll (xs_pollitem_t *items, int nitems, int timeout);

DESCRIPTION

       The xs_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 xs_pollitem_t structure. The nitems argument
       specifies the number of items in the items array. The xs_pollitem_t structure is defined
       as follows:

           typedef struct
           {
               void *socket;
               int fd;
               short events;
               short revents;
           } xs_pollitem_t;

       For each xs_pollitem_t item, xs_poll() shall examine either the Crossroads 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 xs_pollitem_t, the
       Crossroads socket referenced by socket shall take precedence and the value of fd shall be
       ignored.

       For each xs_pollitem_t item, xs_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 xs_pollitem_t item, xs_poll() shall
       wait timeout milliseconds for an event to occur on any of the requested items. If the
       value of timeout is 0, xs_poll() shall return immediately. If the value of timeout is -1,
       xs_poll() shall block indefinitely until a requested event has occurred on at least one
       xs_pollitem_t.

       The events and revents members of xs_pollitem_t are bit masks constructed by OR’ing a
       combination of the following event flags:

       XS_POLLIN
           For Crossroads 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.

       XS_POLLOUT
           For Crossroads 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.

       XS_POLLERR
           For standard sockets, this flag is passed through xs_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 Crossroads sockets this flag has no effect if set in
           events, and shall never be returned in revents by xs_poll().

           Note
           The xs_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 xs_poll() function shall return the number of
       xs_pollitem_t structures with events signaled in revents or 0 if no events have been
       signaled. Upon failure, xs_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
           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 Crossroads socket and a standard socket..

           xs_pollitem_t items [2];
           /* First item refers to Crossroads socket 'socket' */
           items[0].socket = socket;
           items[0].events = XS_POLLIN;
           /* Second item refers to standard socket 'fd' */
           items[1].socket = NULL;
           items[1].fd = fd;
           items[1].events = XS_POLLIN;
           /* Poll for events indefinitely */
           int rc = xs_poll (items, 2, -1);
           assert (rc >= 0);
           /* Returned events will be stored in items[].revents */

SEE ALSO

       xs_socket(3) xs_send(3) xs_recv(3) xs(7)

       Your operating system documentation for the poll() system call.

AUTHORS

       The Crossroads documentation was written by Martin Sustrik <sustrik@250bpm.com[1]> and
       Martin Lucina <martin@lucina.net[2]>.

NOTES

        1. sustrik@250bpm.com
           mailto:sustrik@250bpm.com

        2. martin@lucina.net
           mailto:martin@lucina.net