fsync

/*
 *  call-seq:
 *     ios.fsync   => 0 or nil
 *  
 *  Immediately writes all buffered data in <em>ios</em> to disk.
 *  Returns <code>nil</code> if the underlying operating system does not
 *  support <em>fsync(2)</em>. Note that <code>fsync</code> differs from
 *  using <code>IO#sync=</code>. The latter ensures that data is flushed
 *  from Ruby's buffers, but doesn't not guarantee that the underlying
 *  operating system actually writes it to disk.
 */

static VALUE
rb_io_fsync(io)
    VALUE io;
{
#ifdef HAVE_FSYNC
    OpenFile *fptr;
    FILE *f;

    GetOpenFile(io, fptr);
    f = GetWriteFile(fptr);

    io_fflush(f, fptr);
    if (fsync(fileno(f)) < 0)
        rb_sys_fail(fptr->path);
    return INT2FIX(0);
#else
    rb_notimplement();
    return Qnil;                /* not reached */
#endif
}