/*
 *  call-seq:
 *      mq.closed?   => true or false
 *
 *  Returns +true+ if the message queue descriptor is closed and therefore
 *  unusable, otherwise +false+
 */
static VALUE closed(VALUE self)
{
        struct posix_mq *mq = get(self, 0);

        return mq->des == MQD_INVALID ? Qtrue : Qfalse;
}