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NetBSD 6.1.5 - man page for pollts (netbsd section 2)

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POLL(2) 			     BSD System Calls Manual				  POLL(2)

NAME
     poll, pollts -- synchronous I/O multiplexing

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <poll.h>

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

     #include <poll.h>
     #include <signal.h>
     #include <time.h>

     int
     pollts(struct pollfd * restrict fds, nfds_t nfds, const struct timespec * restrict ts,
	 const sigset_t * restrict sigmask);

DESCRIPTION
     poll() and pollts() examine a set of file descriptors to see if some of them are ready for
     I/O.  The fds argument 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.  If the value in fd is negative, the file descriptor is
		 ignored and revents is set to 0.

     events	 Events to poll for.  (See below.)

     revents	 Events which may occur.  (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.

     POLLRDNORM     Normal data may be read without blocking.

     POLLRDBAND     Data with a non-zero priority may be read without blocking.

     POLLPRI	    High priority data may be read without blocking.

     POLLOUT	    Normal data may be written without blocking.

     POLLWRNORM     Equivalent to POLLOUT.

     POLLWRBAND     Data with a non-zero priority may be written without blocking.

     POLLERR	    An exceptional condition has occurred on the device or socket.  This flag is
		    always checked, even if not present in the events bitmask.

     POLLHUP	    The device or socket has been disconnected.  This flag is always checked,
		    even if not present in the events bitmask.	Note that POLLHUP and POLLOUT
		    should never be present in the revents bitmask at the same time.  If the
		    remote end of a socket is closed, poll() returns a POLLIN event, rather than
		    a POLLHUP.

     POLLNVAL	    The file descriptor is not open.  This flag is always checked, even if not
		    present in the events bitmask.

     If timeout is neither zero nor INFTIM (-1), it specifies a maximum interval to wait for any
     file descriptor to become ready, in milliseconds.	If timeout is INFTIM (-1), the poll
     blocks indefinitely.  If timeout is zero, then poll() will return without blocking.

     If ts is a non-null pointer, it references a timespec structure which specifies a maximum
     interval to wait for any file descriptor to become ready.	If ts is a null pointer, pollts()
     blocks indefinitely.  If ts is a non-null pointer, referencing a zero-valued timespec struc-
     ture, then pollts() will return without blocking.

     If sigmask is a non-null pointer, then the pollts() function shall replace the signal mask
     of the caller by the set of signals pointed to by sigmask before examining the descriptors,
     and shall restore the signal mask of the caller before returning.

RETURN VALUES
     poll() returns the number of descriptors that are ready for I/O, or -1 if an error occurred.
     If the time limit expires, poll() returns 0.  If poll() returns with an error, including one
     due to an interrupted call, the fds array will be unmodified.

COMPATIBILITY
     This implementation differs from the historical one in that a given file descriptor may not
     cause poll() to return with an error.  In cases where this would have happened in the his-
     torical implementation (e.g. trying to poll a revoke(2)d descriptor), this implementation
     instead copies the events bitmask to the revents bitmask.	Attempting to perform I/O on this
     descriptor will then return an error.  This behaviour is believed to be more useful.

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 specified time limit is negative.

SEE ALSO
     accept(2), connect(2), read(2), recv(2), select(2), send(2), write(2)

HISTORY
     The poll() function appeared in AT&T System V Release 3 UNIX.  The pollts() function first
     appeared in NetBSD 3.0.

BUGS
     The distinction between some of the fields in the events and revents bitmasks is really not
     useful without STREAMS.  The fields are defined for compatibility with existing software.

BSD					September 8, 2006				      BSD
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