[MC-101228] Multiple hoppers pointing into each other causes crash for Batching chunks caused by ConcurrentModificationException

Note

The exact reason why this happens is unknown. This bug cannot be reproduced in 1.9. This crash was first mentioned for a normal Survival world in this comment.

The bug

Having many hoppers pointing into each other crashes the game. This crash is caused by a java.util.ConcurrentModificationException (see attached crash report).

How to reproduce

Create a Superflat world with the preset

3;minecraft:hopper:2;1;

1.9.3-pre1

Description: Batching chunks

java.util.ConcurrentModificationException
	at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:901)
	at java.util.ArrayList$Itr.next(ArrayList.java:851)
	at aht.a(SourceFile:1858)
	at ase.a(SourceFile:634)
	at aic.r(SourceFile:63)
	at bqb.b(SourceFile:160)
	at bpx.a(SourceFile:100)
	at bpx.run(SourceFile:43)
	at java.lang.Thread.run(Thread.java:745)