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Crash at handleMobSpawn - Packet24MobSpawn


Mazetar

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When I roam the world I after a while get a crash which seems to be due to a mob spawning and a packet being sent but I'm unable to figure out why and whats wrong.

 

As far as I can tell the packet is of a ID number which is not associated with any entity in the hashmap. On the web I read about a bug in which this happens and that was related to the ID being converted to a byte, this was seemingly only a problem if one registered using EntityRegistry.registerGlobalEntityID.

 

As we are using EntityRegistry.registerModEntity I thought that this would not be a problem, but it seems to be so anyways, or maybe this is a different problem?

 

Here's the log, although it doesn't say much:

 

Description: Exception in world tick

java.lang.NullPointerException
at net.minecraft.client.multiplayer.NetClientHandler.handleMobSpawn(NetClientHandler.java:952)
at net.minecraft.network.packet.Packet24MobSpawn.processPacket(Packet24MobSpawn.java:143)
at net.minecraft.network.MemoryConnection.processReadPackets(MemoryConnection.java:89)
at net.minecraft.client.multiplayer.NetClientHandler.processReadPackets(NetClientHandler.java:281)
at net.minecraft.client.multiplayer.WorldClient.tick(WorldClient.java:99)
at net.minecraft.client.Minecraft.runTick(Minecraft.java:1916)
at net.minecraft.client.Minecraft.runGameLoop(Minecraft.java:898)
at net.minecraft.client.Minecraft.func_99999_d(Minecraft.java:826)
at net.minecraft.client.main.Main.main(Main.java:93)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at net.minecraft.launchwrapper.Launch.launch(Launch.java:57)
at net.minecraft.launchwrapper.Launch.main(Launch.java:18)

 

 

If you guys dont get it.. then well ya.. try harder...

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Hmm this is odd, because all entity registration calls upon one method for registration.

public static int NEXT_MOD_ENTITY_ID = 100;
    
public static void registerModEntity(Class<? extends Entity> clazz, String name, int modID, int trackingRange, int updateFrequency, boolean sendsVelocityUpdates) {
    EntityRegistry.registerModEntity(clazz, name, NEXT_MOD_ENTITY_ID++, DivineRPG.instance, trackingRange, updateFrequency, sendsVelocityUpdates);
}

 

So the modID should never be passed in as 0 hmm

If you guys dont get it.. then well ya.. try harder...

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EntityRegistry.registerModEntity(args) doesn't register any Entity id.

The given modID is internal to Forge, and has nothing to do with the id in EntityList.

You can start your modID at 0, it doesn't matter.

 

The error you are having can be due to left-over from old code. Try in a new world.

Also check that all your entities have a default (World) constructor.

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EntityRegistry.registerModEntity(args) doesn't register any Entity id.

The given modID is internal to Forge, and has nothing to do with the id in EntityList.

You can start your modID at 0, it doesn't matter.

 

The error you are having can be due to left-over from old code. Try in a new world.

Also check that all your entities have a default (World) constructor.

 

Okay well I tested with new worlds, same result but I will go trough all the entities and check that they have a public constructor which takes World as the only argument.

 

Thanks for your help so far :)

If you guys dont get it.. then well ya.. try harder...

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Okay so I went and looked into every entity, and there was one which didn't have the constructor so i fixed it.

But he was never called or spawned by anything in the code.

 

The only thing not having the mentioned constructor are EntityFX's and as far as I can tell they don't have them at all, their super does not accept world as a single argument for any constructor so I assume it's fine as it is :)

 

Now I created three new worlds and I crashed the same crash type on every one of them.

The

 
2013-08-28 00:48:36 [WARNING] [Minecraft-Client] Skipping Entity with id 0 

still shows in the console as well :/

 

If you guys dont get it.. then well ya.. try harder...

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Asking around on the minecraft boards I got the following reply:

Check your code again because registering mob entities does not use Vanilla packets for spawning, e.g., Packet24MobSpawn. It uses FML's EntitySpawnPacket which is sent as Packet250CustomPayload and handled/executed in their own Network Manager.

 

If this is true, then what would be causing the Packet24MobsSpawn to be sent?

I'm using some custom mob spawners, could that be the case? I will try to look into that at least.

 

And even if the above is true, it doesn't explain the "Skipping Entity with id 0" part?

If you guys dont get it.. then well ya.. try harder...

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The only thing not having the mentioned constructor are EntityFX's and as far as I can tell they don't have them at all, their super does not accept world as a single argument for any constructor so I assume it's fine as it is :)

The Entity, which is super of EntityFX, has a World only constructor.

Provided your are registering and making them client-side, I don't see them likely to crash this way.

 

Your custom spawners are worth investigating.

 

Check your code again because registering mob entities does not use Vanilla packets for spawning, e.g., Packet24MobSpawn. It uses FML's EntitySpawnPacket which is sent as Packet250CustomPayload and handled/executed in their own Network Manager.

I didn't know that...I suppose it makes sense since the registration is separated...

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I looked into spawners and as far as I can tell they aren't doing anything weird.

It's just an extension of the vanilla mob spawner except that it takes the entity name as a param which it uses to decide which mob to spawn. And for the spawning it doesn't seem to do anything weird so I dunno but I don't think that's the problem.

 

I've looked into the calling for the Packet24MobSpawn and the only place it's called is during the method getPacketForThisEntity(args) inside EntityTrackerEntry.

 

If it fails several if checks, it ends up at this one here:

else if (!(this.myEntity instanceof IAnimals) && !(this.myEntity instanceof EntityDragon))

If it passes it's packet23 and we are good, if it fails it's packet24MobSpawn.

So if I'm not totally blind now the above sentence means that if the entity inherits from EntityDragon or IAnimals it will result in packet24MobSpawn.

 

Inside the code we have some mobs which extends upon EntityWaterMob and EntityTameable which in turn implements IAnimals!

I'm guessing this could be a possible reason as to why this happens, although I'm not exactly sure as to why we end up at this code place.

So I will now try to go up the calling hierarchy and see what happens futher uo the path.

 

I will try to remove the mobs which extend the mentioned classes / comment them out and if that works I will re-write the entities code to avoid having to extend/implement those classes.

 

If you guys dont get it.. then well ya.. try harder...

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Okay just to test, I set the update velocity to false. That made no difference for the crash.

 

The thing that makes me wonder still is the following line from the log:

2013-08-30 20:49:50 [WARNING] [Minecraft-Client] Skipping Entity with id 0

This happens as soon as I enter a world.

I'd assume there's some entity not being registered properly but I can't figure out which one, as I look at the lists everything seems to be in order.

 

A breakpoint at the two points in the minecraft code which outputs such text reveals that it's output from EntityList.Java when it's createEntityByID is called with ID 0. Resulting in null for the entity found and therefore outputting that msg.

 

The call stack reveals that it's called by NetClientHandler.handleMobSpawn(Packet24MobSpawn) : 951.

The packet contains an EntityID of 1038. O.o

 

If you guys dont get it.. then well ya.. try harder...

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I may have found a solution, by placing a breakpoint at the line creating the packet I thought earlier I could look at every packet and find the one causing the trouble. But I quickly realized that there was insanely many packets of that type being sent.

 

Now I have to admit I was quite thoughtless, I could have done it so much easier.

Conditional breakpoints ftw. By using them to filter out any packet related to vanilla mobs I was able to find the entity responsible for the crash.

 

I found it to be added to the a spawnlist but never registered anywhere.

*sighs* What a relief! I hope this was the only rogue entity in this damn code base.

 

Thank you for all your help GotoLink!

<3

If you guys dont get it.. then well ya.. try harder...

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