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    <title>Mojang Studios Jira</title>
    <link>https://bugs.mojang.com</link>
    <description>This file is an XML representation of an issue</description>
    <language>en</language>    <build-info>
        <version>9.12.2</version>
        <build-number>9120002</build-number>
        <build-date>10-01-2024</build-date>
    </build-info>


<item>
            <title>[MC-509] Exception in server tick loop :: ConcurrentModificationException</title>
                <link>https://bugs.mojang.com/browse/MC-509</link>
                <project id="10400" key="MC">Minecraft: Java Edition</project>
                    <description>&lt;p&gt;It was not obvious what precipitated this crash.  There were several cheaters attempting to fly, but they would get automatically kicked and nothing obvious seemed to go wrong after that.  Then, out of nowhere, the server crashed.&lt;/p&gt;

&lt;p&gt;An administrator did perform an RCON command right before the exception.  This may or may not be related.  The RCON command was:&lt;/p&gt;

&lt;div class=&quot;preformatted panel&quot; style=&quot;border-width: 1px;&quot;&gt;&lt;div class=&quot;preformattedContent panelContent&quot;&gt;
&lt;pre&gt;give &amp;lt;player name&amp;gt; 394 16&lt;/pre&gt;
&lt;/div&gt;&lt;/div&gt;



&lt;div class=&quot;preformatted panel&quot; style=&quot;border-width: 1px;&quot;&gt;&lt;div class=&quot;preformattedContent panelContent&quot;&gt;
&lt;pre&gt;---- Minecraft Crash Report ----
// Don&apos;t be sad, have a hug! &amp;lt;3

Time: 10/25/12 9:46 AM
Description: Exception in server tick loop

java.util.ConcurrentModificationException
        at java.util.HashMap$HashIterator.nextEntry(HashMap.java:894)
        at java.util.HashMap$KeyIterator.next(HashMap.java:928)
        at hz.a(SourceFile:90)
        at net.minecraft.server.MinecraftServer.r(SourceFile:721)
        at hg.r(SourceFile:233)
        at net.minecraft.server.MinecraftServer.q(SourceFile:661)
        at net.minecraft.server.MinecraftServer.run(SourceFile:595)
        at fp.run(SourceFile:818)

Relevant Details:
- Minecraft Version: 1.4.2
- Operating System: Mac OS X (x86_64) version 10.8.1
- Java Version: 1.7.0_07, Oracle Corporation
- Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
- Memory: 703529376 bytes (670 MB) / 3221225472 bytes (3072 MB) up to 3221225472 bytes (3072 MB)
- JVM Flags: 5 total; -Xmx3G -Xms3G -Xloggc:server_gc.log -XX:+UseG1GC -XX:+DisableExplicitGC
- AABB Pool Size: 24234 (1357104 bytes; 1 MB) allocated, 20708 (1159648 bytes; 1 MB) used
- Is Modded: Unknown (can&apos;t tell)
- Profiler Position: N/A (disabled)
- Vec3 Pool Size: 37661 (2109016 bytes; 2 MB) allocated, 19642 (1099952 bytes; 1 MB) used
- Player Count: 9 / 20
- World swim2 Players: 0 total; []
- World swim2 Chunk Stats: ServerChunkCache: 0 Drop: 0
- Type: Dedicated Server&lt;/pre&gt;
&lt;/div&gt;&lt;/div&gt;</description>
                <environment></environment>
        <key id="11776">MC-509</key>
            <summary>Exception in server tick loop :: ConcurrentModificationException</summary>
                <type id="1" iconUrl="https://bugs.mojang.com/secure/viewavatar?size=xsmall&amp;avatarId=18903&amp;avatarType=issuetype">Bug</type>
                                    <status id="5" iconUrl="https://bugs.mojang.com/images/icons/statuses/resolved.png" description="A resolution has been taken, and it is awaiting verification by reporter. From here issues are either reopened, or are closed.">Resolved</status>
                    <statusCategory id="3" key="done" colorName="success"/>
                                    <resolution id="5">Cannot Reproduce</resolution>
                                        <assignee username="-1">Unassigned</assignee>
                                    <reporter username="inertia">Anthony Martin</reporter>
                        <labels>
                            <label>crash</label>
                    </labels>
                <created>Thu, 25 Oct 2012 18:54:36 +0200</created>
                <updated>Sat, 10 Dec 2016 13:32:55 +0100</updated>
                            <resolved>Sun, 6 Dec 2015 19:53:18 +0100</resolved>
                                    <version>Minecraft 1.4.2</version>
                    <version>Minecraft 1.4.6</version>
                    <version>Minecraft 1.4.7</version>
                    <version>Minecraft 1.5</version>
                    <version>Minecraft 1.6.1</version>
                    <version>Minecraft 1.8</version>
                                    <fixVersion>Minecraft 1.6.2</fixVersion>
                                                        <votes>1</votes>
                                    <watches>2</watches>
                                                                            <comments>
                            <comment id="270785" author="kumasasa" created="Sun, 6 Dec 2015 19:53:19 +0100"  >&lt;p&gt;No new reports of this kind since 1.8, but maybe this ticket got superseeded by &lt;a href=&quot;https://bugs.mojang.com/browse/MC-72390&quot; title=&quot;Rcon is not thread-safe&quot; class=&quot;issue-link&quot; data-issue-key=&quot;MC-72390&quot;&gt;&lt;del&gt;MC-72390&lt;/del&gt;&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="202996" author="amn3zik" created="Fri, 10 Oct 2014 22:56:31 +0200"  >&lt;div class=&quot;code panel&quot; style=&quot;border-width: 1px;&quot;&gt;&lt;div class=&quot;codeContent panelContent&quot;&gt;
&lt;pre class=&quot;code-java&quot;&gt;---- Minecraft Crash Report ----
&lt;span class=&quot;code-comment&quot;&gt;// Daisy, daisy...
&lt;/span&gt;
Time: 10/10/14 21:23
Description: Exception in server tick loop

java.util.ConcurrentModificationException
	at java.util.HashMap$HashIterator.nextNode(HashMap.java:1429)
	at java.util.HashMap$KeyIterator.next(HashMap.java:1453)
	at qn.a(SourceFile:166)
	at net.minecraft.server.MinecraftServer.z(SourceFile:615)
	at po.z(SourceFile:305)
	at net.minecraft.server.MinecraftServer.y(SourceFile:531)
	at net.minecraft.server.MinecraftServer.run(SourceFile:447)
	at java.lang.&lt;span class=&quot;code-object&quot;&gt;Thread&lt;/span&gt;.run(&lt;span class=&quot;code-object&quot;&gt;Thread&lt;/span&gt;.java:745)


A detailed walkthrough of the error, its code path and all known details is as follows:
---------------------------------------------------------------------------------------

-- &lt;span class=&quot;code-object&quot;&gt;System&lt;/span&gt; Details --
Details:
	Minecraft Version: 1.8
	Operating &lt;span class=&quot;code-object&quot;&gt;System&lt;/span&gt;: Linux (amd64) version 2.6.32-042stab092.1
	Java Version: 1.8.0_20, Oracle Corporation
	Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
	Memory: 2289190112 bytes (2183 MB) / 5561982976 bytes (5304 MB) up to 10522722304 bytes (10035 MB)
	IntCache: cache: 0, tcache: 0, allocated: 13, tallocated: 95
	Profiler Position: N/A (disabled)
	Player Count: 21 / 80; 
	Is Modded: Unknown (can&apos;t tell)
	Type: Dedicated Server (map_server.txt)
&lt;/pre&gt;
&lt;/div&gt;&lt;/div&gt;</comment>
                            <comment id="116876" author="luckeyjim" created="Thu, 31 Oct 2013 14:38:48 +0100"  >&lt;p&gt;I haven&apos;t seen this in a long time. Currently running 1.7.2. I suspect it is fixed.&lt;/p&gt;</comment>
                            <comment id="94633" author="kumasasa" created="Sat, 27 Jul 2013 00:38:29 +0200"  >&lt;p&gt;Thanks for the feedback.&lt;/p&gt;</comment>
                            <comment id="93319" author="inertia" created="Sun, 21 Jul 2013 02:31:24 +0200"  >&lt;p&gt;I have not observed this situation for quite some time.  I believe it was finally addressed in 1.6.&lt;/p&gt;</comment>
                            <comment id="56027" author="funandjokes" created="Thu, 21 Mar 2013 13:58:38 +0100"  >&lt;p&gt;// You should try our sister game, Minceraft!&lt;/p&gt;

&lt;p&gt;Nice witty comment you got in the crash log . &lt;img class=&quot;emoticon&quot; src=&quot;https://bugs.mojang.com/images/icons/emoticons/smile.png&quot; height=&quot;16&quot; width=&quot;16&quot; align=&quot;absmiddle&quot; alt=&quot;&quot; border=&quot;0&quot;/&gt;&lt;/p&gt;

&lt;p&gt;Actually, confirmed.&lt;/p&gt;</comment>
                            <comment id="53874" author="jwatson0" created="Sat, 16 Mar 2013 04:02:11 +0100"  >&lt;p&gt;+1 on a vanilla server&lt;/p&gt;
&lt;div class=&quot;code panel&quot; style=&quot;border-width: 1px;&quot;&gt;&lt;div class=&quot;codeContent panelContent&quot;&gt;
&lt;pre class=&quot;code-java&quot;&gt;---- Minecraft Crash Report ----
&lt;span class=&quot;code-comment&quot;&gt;// I&apos;m sorry, Dave.
&lt;/span&gt;
Time: 3/15/13 10:32 PM
Description: Exception ticking world

java.util.ConcurrentModificationException
        at java.util.HashMap$HashIterator.nextEntry(HashMap.java:894)
        at java.util.HashMap$KeyIterator.next(HashMap.java:928)
        at iy.b(SourceFile:196)
        at iz.b(SourceFile:122)
        at net.minecraft.server.MinecraftServer.r(SourceFile:454)
        at hz.r(SourceFile:255)
        at net.minecraft.server.MinecraftServer.q(SourceFile:397)
        at net.minecraft.server.MinecraftServer.run(SourceFile:331)
        at gp.run(SourceFile:573)


A detailed walkthrough of the error, its code path and all known details is as follows:
---------------------------------------------------------------------------------------

-- Head --
Stacktrace:
        at java.util.HashMap$HashIterator.nextEntry(HashMap.java:894)
        at java.util.HashMap$KeyIterator.next(HashMap.java:928)
        at iy.b(SourceFile:196)
        at iz.b(SourceFile:122)

-- Affected level --
Details:
        Level name: world
        All players: 1 total; [jc[&lt;span class=&quot;code-quote&quot;&gt;&apos;(REDACTED)&apos;&lt;/span&gt;/2xxxx6, l=&lt;span class=&quot;code-quote&quot;&gt;&apos;world&apos;&lt;/span&gt;, x=-86.80, y=73.00, z=322.70]]
        Chunk stats: ServerChunkCache: 792 Drop: 334
        Level seed: 1290279039577655732
        Level generator: ID 00 - &lt;span class=&quot;code-keyword&quot;&gt;default&lt;/span&gt;, ver 1. Features enabled: &lt;span class=&quot;code-keyword&quot;&gt;true&lt;/span&gt;
        Level generator options: 
        Level spawn location: World: (-111,64,286), Chunk: (at 1,4,14 in -7,17; contains blocks -112,0,272 to -97,255,287), Region: (-1,0; contains chunks -32,0 to -1,31, blocks -512,0,0 to -1,255,511)
        Level time: 377270 game time, 127553 day time
        Level dimension: 0
        Level storage version: 0x04ABD - Anvil
        Level weather: Rain time: 49967 (now: &lt;span class=&quot;code-keyword&quot;&gt;false&lt;/span&gt;), thunder time: 112422 (now: &lt;span class=&quot;code-keyword&quot;&gt;false&lt;/span&gt;)
        Level game mode: Game mode: survival (ID 0). Hardcore: &lt;span class=&quot;code-keyword&quot;&gt;false&lt;/span&gt;. Cheats: &lt;span class=&quot;code-keyword&quot;&gt;false&lt;/span&gt;
Stacktrace:
        at net.minecraft.server.MinecraftServer.r(SourceFile:454)
        at hz.r(SourceFile:255)
        at net.minecraft.server.MinecraftServer.q(SourceFile:397)
        at net.minecraft.server.MinecraftServer.run(SourceFile:331)
        at gp.run(SourceFile:573)

-- &lt;span class=&quot;code-object&quot;&gt;System&lt;/span&gt; Details --
Details:
        Minecraft Version: 1.5
        Operating &lt;span class=&quot;code-object&quot;&gt;System&lt;/span&gt;: Linux (i386) version 2.6.31.5-127.fc12.i686.PAE
        Java Version: 1.7.0_10, Oracle Corporation
        Java VM Version: Java HotSpot(TM) Client VM (mixed mode, sharing), Oracle Corporation
        Memory: 1574450160 bytes (1501 MB) / 2075918336 bytes (1979 MB) up to 2075918336 bytes (1979 MB)
        JVM Flags: 2 total; -Xmx2G -Xms2G
        AABB Pool Size: 5973 (334488 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used
        Suspicious classes: No suspicious classes found.
        IntCache: cache: 0, tcache: 0, allocated: 1, tallocated: 63
        Profiler Position: N/A (disabled)
        Vec3 Pool Size: 1481 (82936 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used
        Player Count: 1 / 20; [jc[&lt;span class=&quot;code-quote&quot;&gt;&apos;(REDACTED)&apos;&lt;/span&gt;/2xxxx6, l=&lt;span class=&quot;code-quote&quot;&gt;&apos;world&apos;&lt;/span&gt;, x=-86.80, y=73.00, z=322.70]]
        Is Modded: Unknown (can&apos;t tell)
        Type: Dedicated Server (map_server.txt)&lt;/pre&gt;
&lt;/div&gt;&lt;/div&gt;</comment>
                            <comment id="52716" author="luckeyjim" created="Thu, 14 Mar 2013 02:34:05 +0100"  >&lt;p&gt;I just got something similar in 1.5. Brand new world, no RCON. There were two of us on, but the trace says just one, so this might have happened just after the other guy disconnected. No mods, no DDoS, nothing special at all.&lt;/p&gt;

&lt;div class=&quot;code panel&quot; style=&quot;border-width: 1px;&quot;&gt;&lt;div class=&quot;codeContent panelContent&quot;&gt;
&lt;pre class=&quot;code-java&quot;&gt;---- Minecraft Crash Report ----
&lt;span class=&quot;code-comment&quot;&gt;// You should &lt;span class=&quot;code-keyword&quot;&gt;try&lt;/span&gt; our sister game, Minceraft!
&lt;/span&gt;
Time: 3/13/13 7:56 PM
Description: Exception ticking world

java.util.ConcurrentModificationException
	at java.util.HashMap$HashIterator.nextEntry(HashMap.java:894)
	at java.util.HashMap$KeyIterator.next(HashMap.java:928)
	at iy.b(SourceFile:196)
	at iz.b(SourceFile:122)
	at net.minecraft.server.MinecraftServer.r(SourceFile:454)
	at hz.r(SourceFile:255)
	at net.minecraft.server.MinecraftServer.q(SourceFile:397)
	at net.minecraft.server.MinecraftServer.run(SourceFile:331)
	at gp.run(SourceFile:573)


A detailed walkthrough of the error, its code path and all known details is as follows:
---------------------------------------------------------------------------------------

-- Head --
Stacktrace:
	at java.util.HashMap$HashIterator.nextEntry(HashMap.java:894)
	at java.util.HashMap$KeyIterator.next(HashMap.java:928)
	at iy.b(SourceFile:196)
	at iz.b(SourceFile:122)

-- Affected level --
Details:
	Level name: world
	All players: 1 total; [jc[&lt;span class=&quot;code-quote&quot;&gt;&apos;LuckeyJim&apos;&lt;/span&gt;/7448, l=&lt;span class=&quot;code-quote&quot;&gt;&apos;world&apos;&lt;/span&gt;, x=-537.24, y=51.17, z=207.48]]
	Chunk stats: ServerChunkCache: 972 Drop: 125
	Level seed: 2106225363214519273
	Level generator: ID 00 - &lt;span class=&quot;code-keyword&quot;&gt;default&lt;/span&gt;, ver 1. Features enabled: &lt;span class=&quot;code-keyword&quot;&gt;true&lt;/span&gt;
	Level generator options: 
	Level spawn location: World: (-426,64,255), Chunk: (at 6,4,15 in -27,15; contains blocks -432,0,240 to -417,255,255), Region: (-1,0; contains chunks -32,0 to -1,31, blocks -512,0,0 to -1,255,511)
	Level time: 90082 game time, 90082 day time
	Level dimension: 0
	Level storage version: 0x04ABD - Anvil
	Level weather: Rain time: 15721 (now: &lt;span class=&quot;code-keyword&quot;&gt;false&lt;/span&gt;), thunder time: 13873 (now: &lt;span class=&quot;code-keyword&quot;&gt;false&lt;/span&gt;)
	Level game mode: Game mode: survival (ID 0). Hardcore: &lt;span class=&quot;code-keyword&quot;&gt;false&lt;/span&gt;. Cheats: &lt;span class=&quot;code-keyword&quot;&gt;false&lt;/span&gt;
Stacktrace:
	at net.minecraft.server.MinecraftServer.r(SourceFile:454)
	at hz.r(SourceFile:255)
	at net.minecraft.server.MinecraftServer.q(SourceFile:397)
	at net.minecraft.server.MinecraftServer.run(SourceFile:331)
	at gp.run(SourceFile:573)

-- &lt;span class=&quot;code-object&quot;&gt;System&lt;/span&gt; Details --
Details:
	Minecraft Version: 1.5
	Operating &lt;span class=&quot;code-object&quot;&gt;System&lt;/span&gt;: Linux (i386) version 3.7.10-1-ARCH
	Java Version: 1.7.0_15, Oracle Corporation
	Java VM Version: OpenJDK Client VM (mixed mode), Oracle Corporation
	Memory: 77103736 bytes (73 MB) / 185393152 bytes (176 MB) up to 778502144 bytes (742 MB)
	JVM Flags: 2 total; -Xms128M -Xmx768M
	AABB Pool Size: 5420 (303520 bytes; 0 MB) allocated, 4 (224 bytes; 0 MB) used
	Suspicious classes: No suspicious classes found.
	IntCache: cache: 0, tcache: 0, allocated: 3, tallocated: 63
	Profiler Position: N/A (disabled)
	Vec3 Pool Size: 14605 (817880 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used
	Player Count: 1 / 8; [jc[&lt;span class=&quot;code-quote&quot;&gt;&apos;LuckeyJim&apos;&lt;/span&gt;/7448, l=&lt;span class=&quot;code-quote&quot;&gt;&apos;world&apos;&lt;/span&gt;, x=-537.24, y=51.17, z=207.48]]
	Is Modded: Unknown (can&apos;t tell)
	Type: Dedicated Server (map_server.txt)&lt;/pre&gt;
&lt;/div&gt;&lt;/div&gt;</comment>
                            <comment id="25790" author="inertia" created="Fri, 30 Nov 2012 02:15:50 +0100"  >&lt;p&gt;I have seen a great many ConcurrentModificationException spamming the console in 1.4.5 while the server is being DDoSed.  Likely, this is a side effect of the garbage collector being overworked.  This is one of those &quot;tricky-to-re-produce&quot; situations.  I can&apos;t exactly ask someone to DDoS my server so I can test it.&lt;/p&gt;

&lt;p&gt;Your call.&lt;/p&gt;</comment>
                            <comment id="25784" author="bljat" created="Fri, 30 Nov 2012 01:58:00 +0100"  >&lt;p&gt;Is this still a concern in the current Minecraft version? If so, please update the affected versions in order to best aid Mojang ensuring bugs are still valid in the latest releases/pre-releases.&lt;/p&gt;</comment>
                            <comment id="13697" author="inertia" created="Fri, 26 Oct 2012 00:48:34 +0200"  >&lt;p&gt;It appears that RCON commands do indeed have something to do with it, but only when the server has been up for quite a while.&lt;/p&gt;</comment>
                    </comments>
                <issuelinks>
                            <issuelinktype id="10102">
                    <name>Duplicate</name>
                                                                <inwardlinks description="is duplicated by">
                                        <issuelink>
            <issuekey id="40819">MC-21813</issuekey>
        </issuelink>
                            </inwardlinks>
                                    </issuelinktype>
                            <issuelinktype id="10103">
                    <name>Relates</name>
                                                                <inwardlinks description="relates to">
                                        <issuelink>
            <issuekey id="42277">MC-23105</issuekey>
        </issuelink>
            <issuelink>
            <issuekey id="100212">MC-72390</issuekey>
        </issuelink>
            <issuelink>
            <issuekey id="157501">MC-111295</issuekey>
        </issuelink>
            <issuelink>
            <issuekey id="17823">MC-5245</issuekey>
        </issuelink>
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