glibc/sysdeps/unix/bsd/poll.c

/* Copyright (C) 1994-2013 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <http://www.gnu.org/licenses/>.  */

#include <alloca.h>
#include <sys/poll.h>
#include <sys/types.h>
#include <errno.h>
#include <string.h>
#include <sys/time.h>
#include <sys/param.h>
#include <unistd.h>

/* Poll the file descriptors described by the NFDS structures starting at
   FDS.  If TIMEOUT is nonzero and not -1, allow TIMEOUT milliseconds for
   an event to occur; if TIMEOUT is -1, block until an event occurs.
   Returns the number of file descriptors with events, zero if timed out,
   or -1 for errors.  */

int
__poll (fds, nfds, timeout)
     struct pollfd *fds;
     nfds_t nfds;
     int timeout;
{
  static int max_fd_size;
  struct timeval tv;
  fd_set *rset, *wset, *xset;
  struct pollfd *f;
  int ready;
  int maxfd = 0;
  int bytes;

  if (!max_fd_size)
    max_fd_size = __getdtablesize ();

  bytes = howmany (max_fd_size, __NFDBITS);
  rset = alloca (bytes);
  wset = alloca (bytes);
  xset = alloca (bytes);

  /* We can't call FD_ZERO, since FD_ZERO only works with sets
     of exactly __FD_SETSIZE size.  */
  __bzero (rset, bytes);
  __bzero (wset, bytes);
  __bzero (xset, bytes);

  for (f = fds; f < &fds[nfds]; ++f)
    {
      f->revents = 0;
      if (f->fd >= 0)
	{
	  if (f->fd >= max_fd_size)
	    {
	      /* The user provides a file descriptor number which is higher
		 than the maximum we got from the `getdtablesize' call.
		 Maybe this is ok so enlarge the arrays.  */
	      fd_set *nrset, *nwset, *nxset;
	      int nbytes;

	      max_fd_size = roundup (f->fd, __NFDBITS);
	      nbytes = howmany (max_fd_size, __NFDBITS);

	      nrset = alloca (nbytes);
	      nwset = alloca (nbytes);
	      nxset = alloca (nbytes);

	      __bzero ((char *) nrset + bytes, nbytes - bytes);
	      __bzero ((char *) nwset + bytes, nbytes - bytes);
	      __bzero ((char *) nxset + bytes, nbytes - bytes);

	      rset = memcpy (nrset, rset, bytes);
	      wset = memcpy (nwset, wset, bytes);
	      xset = memcpy (nxset, xset, bytes);

	      bytes = nbytes;
	    }

	  if (f->events & POLLIN)
	    FD_SET (f->fd, rset);
	  if (f->events & POLLOUT)
	    FD_SET (f->fd, wset);
	  if (f->events & POLLPRI)
	    FD_SET (f->fd, xset);
	  if (f->fd > maxfd && (f->events & (POLLIN|POLLOUT|POLLPRI)))
	    maxfd = f->fd;
	}
    }

  tv.tv_sec = timeout / 1000;
  tv.tv_usec = (timeout % 1000) * 1000;

  while (1)
    {
      ready = __select (maxfd + 1, rset, wset, xset,
			timeout == -1 ? NULL : &tv);

      /* It might be that one or more of the file descriptors is invalid.
	 We now try to find and mark them and then try again.  */
      if (ready == -1 && errno == EBADF)
	{
	  fd_set *sngl_rset = alloca (bytes);
	  fd_set *sngl_wset = alloca (bytes);
	  fd_set *sngl_xset = alloca (bytes);
	  struct timeval sngl_tv;

	  /* Clear the original set.  */
	  __bzero (rset, bytes);
	  __bzero (wset, bytes);
	  __bzero (xset, bytes);

	  /* This means we don't wait for input.  */
	  sngl_tv.tv_sec = 0;
	  sngl_tv.tv_usec = 0;

	  maxfd = -1;

	  /* Reset the return value.  */
	  ready = 0;

	  for (f = fds; f < &fds[nfds]; ++f)
	    if (f->fd != -1 && (f->events & (POLLIN|POLLOUT|POLLPRI))
		&& (f->revents & POLLNVAL) == 0)
	      {
		int n;

		__bzero (sngl_rset, bytes);
		__bzero (sngl_wset, bytes);
		__bzero (sngl_xset, bytes);

		if (f->events & POLLIN)
		  FD_SET (f->fd, sngl_rset);
		if (f->events & POLLOUT)
		  FD_SET (f->fd, sngl_wset);
		if (f->events & POLLPRI)
		  FD_SET (f->fd, sngl_xset);

		n = __select (f->fd + 1, sngl_rset, sngl_wset, sngl_xset,
			      &sngl_tv);
		if (n != -1)
		  {
		    /* This descriptor is ok.  */
		    if (f->events & POLLIN)
		      FD_SET (f->fd, rset);
		    if (f->events & POLLOUT)
		      FD_SET (f->fd, wset);
		    if (f->events & POLLPRI)
		      FD_SET (f->fd, xset);
		    if (f->fd > maxfd)
		      maxfd = f->fd;
		    if (n > 0)
		      /* Count it as being available.  */
		      ++ready;
		  }
		else if (errno == EBADF)
		  f->revents |= POLLNVAL;
	      }
	  /* Try again.  */
	  continue;
	}

      break;
    }

  if (ready > 0)
    for (f = fds; f < &fds[nfds]; ++f)
      {
	if (f->fd >= 0)
	  {
	    if (FD_ISSET (f->fd, rset))
	      f->revents |= POLLIN;
	    if (FD_ISSET (f->fd, wset))
	      f->revents |= POLLOUT;
	    if (FD_ISSET (f->fd, xset))
	      f->revents |= POLLPRI;
	  }
      }

  return ready;
}
#ifndef __poll
libc_hidden_def (__poll)
weak_alias (__poll, poll)
#endif