/* Approximate posix_close and POSIX_CLOSE_RESTART well enough for Emacs.
   For the background behind this mess, please see Austin Group defect 529
   <http://austingroupbugs.net/view.php?id=529>.  */

#ifndef POSIX_CLOSE_RESTART
# define POSIX_CLOSE_RESTART 1
static int
posix_close (int fd, int flag)
{
  /* Only the POSIX_CLOSE_RESTART case is emulated.  */
  eassert (flag == POSIX_CLOSE_RESTART);

  /* Things are tricky if close (fd) returns -1 with errno == EINTR
     on a system that does not define POSIX_CLOSE_RESTART.

     In this case, in some systems (e.g., GNU/Linux, AIX) FD is
     closed, and retrying the close could inadvertently close a file
     descriptor allocated by some other thread.  In other systems
     (e.g., HP/UX) FD is not closed.  And in still other systems
     (e.g., macOS, Solaris), maybe FD is closed, maybe not, and in a
     multithreaded program there can be no way to tell.

     So, in this case, pretend that the close succeeded.  This works
     well on systems like GNU/Linux that close FD.  Although it may
     leak a file descriptor on other systems, the leak is unlikely and
     it's better to leak than to close a random victim.  */
  return close (fd) == 0 || errno == EINTR ? 0 : -1;
}
#endif

/* Close FD, retrying if interrupted.  If successful, return 0;
   otherwise, return -1 and set errno to a non-EINTR value.  Consider
   an EINPROGRESS error to be successful, as that's merely a signal
   arriving.  FD is always closed when this function returns, even
   when it returns -1.

   Do not call this function if FD is nonnegative and might already be closed,
   as that might close an innocent victim opened by some other thread.  */

int
emacs_close (int fd)
{
  while (1)
    {
      int r = posix_close (fd, POSIX_CLOSE_RESTART);
      if (r == 0)
	return r;
      if (!POSIX_CLOSE_RESTART || errno != EINTR)
	{
	  eassert (errno != EBADF || fd < 0);
	  return errno == EINPROGRESS ? 0 : r;
	}
    }
}