Multi Threaded update to List of TriggeredAbilities - Why and how to avoid?

[LevelX2]

BetaSteward reverted the list of triggeredabilities recently back to HashMap from ConcurrentHashMap with this commit: fcb9bc9.

Now again the ConcurrentModificationExceptions happen on servers.
http://www.slightlymagic.net/forum/viewtopic.php?f=70&t=17186&p=178870#p178870
http://www.slightlymagic.net/forum/viewtopic.php?f=70&t=17186&start=30#p179083

First issue was #473.

Checking for the reason is needed and resolving the issue in one or the other way.

[BetaSteward]

I did a lot of tests without ConcurrentHashMap and I didn't get any errors. I guess that there might be some cases were the TriggeredAbilities list is modified while it is being traversed. This could throw a ConcurrentModificationException.

I think it should be fine to change it back to ConcurrentHashMap. The performance saving is not that great.

[LevelX2]

I assume there are triggered abilities that add triggered abilites that cause this problem. So probably the update won't be caused by another thread. But I'm not sure because the ability will only be put onto the stack on not resolve yet.

Chnaged it back to ConcurrentHashMap.