Problem Corrupted chunks, concurrent modification exception to blame?

[Francis Baster]

Hi there, for a long time my FTB Ultimate server has been spamming the console with this Concurrent Modification Exception:

Spoiler

2013-05-07 05:00:23 [INFO] [STDERR] java.util.ConcurrentModificationException
2013-05-07 05:00:23 [INFO] [STDERR]at java.util.HashMap$HashIterator.nextEntry(Unknown Source)
2013-05-07 05:00:23 [INFO] [STDERR]at java.util.HashMap$ValueIterator.next(Unknown Source)
2013-05-07 05:00:23 [INFO] [STDERR]at bq.a(SourceFile:24)
2013-05-07 05:00:23 [INFO] [STDERR]at cd.a(SourceFile:114)
2013-05-07 05:00:23 [INFO] [STDERR]at bq.a(SourceFile:25)
2013-05-07 05:00:23 [INFO] [STDERR]at cd.a(SourceFile:114)
2013-05-07 05:00:23 [INFO] [STDERR]at bq.a(SourceFile:25)
2013-05-07 05:00:23 [INFO] [STDERR]at by.a(SourceFile:26)
2013-05-07 05:00:23 [INFO] [STDERR]at cd.a(SourceFile:114)
2013-05-07 05:00:23 [INFO] [STDERR]at bq.a(SourceFile:25)
2013-05-07 05:00:23 [INFO] [STDERR]at cd.a(SourceFile:114)
2013-05-07 05:00:23 [INFO] [STDERR]at bq.a(SourceFile:25)
2013-05-07 05:00:23 [INFO] [STDERR]at cd.a(SourceFile:114)
2013-05-07 05:00:23 [INFO] [STDERR]at ca.a(CompressedStreamTools.java:140)
2013-05-07 05:00:23 [INFO] [STDERR]at aam.a(AnvilChunkLoader.java:198)
2013-05-07 05:00:23 [INFO] [STDERR]at aam.c(AnvilChunkLoader.java:184)
2013-05-07 05:00:23 [INFO] [STDERR]at aiw.b(SourceFile:29)
2013-05-07 05:00:23 [INFO] [STDERR]at aiw.run(SourceFile:22)
2013-05-07 05:00:23 [INFO] [STDERR]at java.lang.Thread.run(Unknown Source)

I think this is a fairly common warning and most people are told just to ignore them.
Occasionally chunks on my server regenerate themselves, much to the annoyance of people who have built there. Today I was on the console as a chunk regenerated and saw this alarming message which bears some resemblance to the concurrent modification spam:

Spoiler

2013-05-07 04:38:00 [INFO] [STDOUT] Chunk file at -7,-56 is in the wrong location; relocating. (Expected -7, -56, got -8, -56)
2013-05-07 04:38:00 [INFO] [STDOUT] Chunk file at -8,-56 is in the wrong location; relocating. (Expected -8, -56, got -3, -56)
2013-05-07 04:38:00 [INFO] [STDOUT] Chunk file at -3,-56 is in the wrong location; relocating. (Expected -3, -56, got -7, -56)
2013-05-07 04:43:30 [INFO] [STDOUT] Wrong location! qr['Zombie'/12989, l='world', x=-104.50, y=13.00, z=-893.50]
2013-05-07 04:43:30 [INFO] [STDERR] java.lang.Exception: Stack trace
2013-05-07 04:43:30 [INFO] [STDERR]at java.lang.Thread.dumpStack(Unknown Source)
2013-05-07 04:43:30 [INFO] [STDERR]at zz.a(Chunk.java:923)
2013-05-07 04:43:30 [INFO] [STDERR]at aam.a(AnvilChunkLoader.java:406)
2013-05-07 04:43:30 [INFO] [STDERR]at aam.a(AnvilChunkLoader.java:103)
2013-05-07 04:43:30 [INFO] [STDERR]at aam.a(AnvilChunkLoader.java:83)
2013-05-07 04:43:30 [INFO] [STDERR]at im.f(ChunkProviderServer.java:182)
2013-05-07 04:43:30 [INFO] [STDERR]at im.c(ChunkProviderServer.java:118)
2013-05-07 04:43:30 [INFO] [STDERR]at im.d(ChunkProviderServer.java:166)
2013-05-07 04:43:30 [INFO] [STDERR]at yc.e(World.java:524)
2013-05-07 04:43:30 [INFO] [STDERR]at in.g(WorldServer.java:331)
2013-05-07 04:43:30 [INFO] [STDERR]at in.b(WorldServer.java:180)
2013-05-07 04:43:30 [INFO] [STDERR]at net.minecraft.server.MinecraftServer.r(MinecraftServer.java:669)
2013-05-07 04:43:30 [INFO] [STDERR]at ho.r(DedicatedServer.java:269)
2013-05-07 04:43:30 [INFO] [STDERR]at net.minecraft.server.MinecraftServer.q(MinecraftServer.java:599)
2013-05-07 04:43:30 [INFO] [STDERR]at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:497)
2013-05-07 04:43:30 [INFO] [STDERR]at fy.run(SourceFile:849)

So I was wondering:
1) What causes the concurrent modification exception to be spammed
2) Is it possible that the corrupted chunks are being caused by the CM exception?

Any help is appreciated, cheers.

 

[TheTechWhizNumberOne]

1. the concurrentModificationExeption is when two java Threads colide/conflict
2. they are defiantly caused by the concurentModificationExeption (i have experienced this myself) i do believe that it is a forge issue, try changing your forge versoin see what happens