int
     poll(struct pollfd *fds, nfds_t nfds, int timeout);

DESCRIPTION

     Poll() examines a set of file descriptors to see if some of them are
     ready for I/O or if certain events have occurred on them.  The fds argu-
     ment is a pointer to an array of pollfd structures as defined in <poll.h>
     (shown below).  The nfds argument determines the size of the fds array.

     struct pollfd {
         int    fd;       /* file descriptor */
         short  events;   /* events to look for */
         short  revents;  /* events returned */
     };

     The fields of struct pollfd are as follows:

     fd          File descriptor to poll.

     events      Events to poll for.  (See below.)

     revents     Events which may occur or have occurred.  (See below.)

     The event bitmasks in events and revents have the following bits:

     POLLIN         Data other than high priority data may be read without
                    blocking.  This is equivalent to ( POLLRDNORM | POLLRDBAND
                    ).

     POLLRDNORM     Normal data may be read without blocking.

     POLLRDBAND     Priority data may be read without blocking.

     POLLPRI        High priority data may be read without blocking.

     POLLOUT

     POLLWRNORM     Normal data may be written without blocking.

     POLLWRBAND     Priority data may be written without blocking.

     POLLERR        An exceptional condition has occurred on the device or
                    socket.  This flag is output only, and ignored if present
                    in the input events bitmask.

     POLLHUP        The device or socket has been disconnected.  This flag is
                    output only, and ignored if present in the input events
                    bitmask.  Note that POLLHUP and POLLOUT are mutually
                    exclusive and should never be present in the revents bit-
                    mask at the same time.

     poll() returns with an error, including one due to an interrupted call,
     the fds array will be unmodified.

ERRORS

     An error return from poll() indicates:

     [EFAULT]           Fds points outside the process's allocated address
                        space.

     [EINTR]            A signal was delivered before the time limit expired
                        and before any of the selected events occurred.

     [EINVAL]           The nfds argument is greater than OPEN_MAX, or the
                        timeout argument is less than -1.

BUGS

     The poll() system call currently does not support devices.

SEE ALSO

     accept(2), connect(2), kevent(2), read(2), recv(2), select(2), send(2),
     write(2)

HISTORY

     The poll() function call appeared in AT&T System V UNIX.


BSD                            February 27, 2005                           BSD