poll.c

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/* Copyright (C) 1994, 1996, 1997, 1998, 1999 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 Library General Public License as
   published by the Free Software Foundation; either version 2 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
   Library General Public License for more details.

   You should have received a copy of the GNU Library General Public
   License along with the GNU C Library; see the file COPYING.LIB.  If not,
   write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
   Boston, MA 02111-1307, USA.  */

/*
 * $Id: poll.c,v 1.1 2002-12-05 01:50:22 rtv Exp $
 *
 * taken from glibc, modified slightly for standalone compilation, and used as
 * a fallback implementation when poll() is not available. - BPG
 */

#include "replace.h"

//#include <alloca.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(struct pollfd* fds, unsigned long int 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;
}