default Accumulator<T, ?, R> synced() {
		return synced(this);
	}
Returns a synchronized (thread-safe) accumulator backed by {@code this}
accumulator. {@code this} accumulator is used as a synchronization object.

@return a synchronized (thread-safe) accumulator backed by {@code this}
	       accumulator
jenetics/src/main/java/io/jenetics/util/Accumulator.java