@Override
        public boolean tryAdvance(Consumer<? super T> action) {
            return buffering // volatile-read (ensures buffer is up-to-date)
                  ? tryAdvanceThisWithBuffering(action) // slow (synchronized)
                  : tryAdvanceThisAtOnce(action); // fast (not synchronized)
        }
Index of the element that will be returned upon next call to <code>tryAdvance</code> if such element exists.
jOOL/src/main/java/org/jooq/lambda/SeqBuffer.java