Shenandoah introduced fast code roots iteration (ShenandoahCodeRootsStyle = 2), also kept 2 additional iteration mechanism (ShenandoahCodeRootsStyle = 0 and 1), mainly for verification purpose.

Today, Shenandoah normally iterates code roots concurrently using style 2, while style 0 and 1 require safepoints, that makes style 0 and 1 verification less useful. Besides, Shenandoah has much improved verifier, more suitable for the purpose.