libc/winsup/cygwin/poll.cc

/* poll.cc. Implements poll(2) via usage of select(2) call.

   This file is part of Cygwin.

   This software is a copyrighted work licensed under the terms of the
   Cygwin license.  Please consult the file "CYGWIN_LICENSE" for
   details. */

#define FD_SETSIZE 16384		// lots of fds
#include "winsup.h"
#include <sys/poll.h>
#include <sys/param.h>
#include <stdlib.h>
#define USE_SYS_TYPES_FD_SET
#include "cygerrno.h"
#include "path.h"
#include "fhandler.h"
#include "dtable.h"
#include "cygheap.h"
#include "pinfo.h"
#include "sigproc.h"
#include "select.h"

extern "C" int
poll (struct pollfd *fds, nfds_t nfds, int timeout)
{
  int max_fd = 0;
  int invalid_fds = 0;
  fd_set *read_fds, *write_fds, *except_fds;
  struct timeval tv = { timeout / 1000, (timeout % 1000) * 1000 };

  for (unsigned int i = 0; i < nfds; ++i)
    if (fds[i].fd > max_fd)
      max_fd = fds[i].fd;

  size_t fds_size = howmany (max_fd + 1, NFDBITS) * sizeof (fd_mask);

  read_fds = (fd_set *) alloca (fds_size);
  write_fds = (fd_set *) alloca (fds_size);
  except_fds = (fd_set *) alloca (fds_size);

  if (!read_fds || !write_fds || !except_fds)
    {
      set_errno (EINVAL);	/* According to SUSv3. */
      return -1;
    }

  memset (read_fds, 0, fds_size);
  memset (write_fds, 0, fds_size);
  memset (except_fds, 0, fds_size);

  for (unsigned int i = 0; i < nfds; ++i)
    {
      fds[i].revents = 0;
      if (!cygheap->fdtab.not_open (fds[i].fd))
	{
	  if (fds[i].events & POLLIN)
	    FD_SET(fds[i].fd, read_fds);
	  if (fds[i].events & POLLOUT)
	    FD_SET(fds[i].fd, write_fds);
	  if (fds[i].events & POLLPRI)
	    FD_SET(fds[i].fd, except_fds);
	}
      else if (fds[i].fd >= 0)
	{
	  ++invalid_fds;
	  fds[i].revents = POLLNVAL;
	}
    }

  /* Invalid fds? */
  if (invalid_fds > 0)
    {
      /* Only invalid fds?  Return. */
      if ((nfds_t) invalid_fds == nfds)
	return invalid_fds;
      /* POSIX doesn't explicitely define this behaviour, but on Linux,
	 the timeout is set to 0 if an error occurs, and POLLNVAL is one
	 of these errors.  So, for Linux-compatibility's sake... */
      tv.tv_sec = tv.tv_usec = 0;
    }

  int ret = cygwin_select (max_fd + 1, read_fds, write_fds, except_fds,
			   timeout < 0 ? NULL : &tv);
  /* timeout, signal, whatever?  Return.  If invalid fds exist, return with
     their number. */
  if (ret <= 0)
    return invalid_fds ?: ret;

  /* Set revents fields and count fds with non-zero revents fields for
     return value. */
  ret = 0;
  for (unsigned int i = 0; i < nfds; ++i)
    {
      if (fds[i].fd >= 0 && fds[i].revents != POLLNVAL)
	{
	  fhandler_socket_wsock *sock;

	  /* Check if the descriptor has been closed, or if shutdown for the
	     read side has been called on a socket. */
	  if (cygheap->fdtab.not_open (fds[i].fd)
	      || ((sock = cygheap->fdtab[fds[i].fd]->is_wsock_socket ())
		  && sock->saw_shutdown_read ()))
	    fds[i].revents = POLLHUP;
	  else
	    {
	      if (FD_ISSET(fds[i].fd, read_fds))
		/* This should be sufficient for sockets, too.  Using
		   MSG_PEEK, as before, can be considered dangerous at
		   best.  Quote from W. Richard Stevens: "The presence
		   of an error can be considered either normal data or
		   an error (POLLERR).  In either case, a subsequent read
		   will return -1 with errno set to the appropriate value."
		   So it looks like there's actually no good reason to
		   return POLLERR. */
		fds[i].revents |= POLLIN;
	      /* Handle failed connect.  A failed connect implicitly sets
	         POLLOUT, if requested, but it doesn't set POLLIN. */
	      if ((fds[i].events & POLLIN)
		  && (sock = cygheap->fdtab[fds[i].fd]->is_wsock_socket ())
		  && sock->connect_state () == connect_failed)
		fds[i].revents |= (POLLIN | POLLERR);
	      else
		{
		  if (FD_ISSET(fds[i].fd, write_fds))
		    fds[i].revents |= POLLOUT;
		  if (FD_ISSET(fds[i].fd, except_fds))
		    fds[i].revents |= POLLPRI;
		}
	    }
	  if (fds[i].revents)
	    ++ret;
	}
    }
  /* Number of fds with event includes the invalid fds. */
  return ret + invalid_fds;
}

extern "C" int
ppoll (struct pollfd *fds, nfds_t nfds, const struct timespec *timeout_ts,
       const sigset_t *sigmask)
{
  int timeout;
  sigset_t oldset = _my_tls.sigmask;

  __try
    {
      timeout = (timeout_ts == NULL)
		? -1
		: (timeout_ts->tv_sec * 1000 + timeout_ts->tv_nsec / 1000000);
      if (sigmask)
	set_signal_mask (_my_tls.sigmask, *sigmask);
      int ret = poll (fds, nfds, timeout);
      if (sigmask)
	set_signal_mask (_my_tls.sigmask, oldset);
      return ret;
    }
  __except (EFAULT) {}
  __endtry
  return -1;
}