Okay, I made some progress based on suspicion that the lighting is causing the trouble. If you trace the code for setBlock, as mentioned before it updates the lighting. There are a few variables that control this and it seems that the whole thing is skipped if the world.provider.hasNoSky is true.

 

So I did a test where I set hasNoSky to true right before the generation loop, then set it back to false immediately after. Sure enough, the generation at height of 133 was just as fast (4 seconds) as generation at ground level.

 

[22:09:51] [server thread/ERROR]: Encountered an unexpected exception

net.minecraft.util.ReportedException: Exception ticking world

at net.minecraft.server.MinecraftServer.updateTimeLightAndEntities(MinecraftServer.java:698) ~[MinecraftServer.class:?]

at net.minecraft.server.MinecraftServer.tick(MinecraftServer.java:614) ~[MinecraftServer.class:?]

at net.minecraft.server.integrated.IntegratedServer.tick(IntegratedServer.java:118) ~[integratedServer.class:?]

at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:485) [MinecraftServer.class:?]

at net.minecraft.server.MinecraftServer$2.run(MinecraftServer.java:752) [MinecraftServer$2.class:?]

Caused by: java.lang.NullPointerException

at net.minecraft.world.chunk.storage.ExtendedBlockStorage.getExtSkylightValue(ExtendedBlockStorage.java:164) ~[ExtendedBlockStorage.class:?]

at net.minecraft.world.chunk.Chunk.getBlockLightValue(Chunk.java:824) ~[Chunk.class:?]

at net.minecraft.world.World.getFullBlockLightValue(World.java:857) ~[World.class:?]

at net.minecraft.world.World.func_147467_a(World.java:3133) ~[World.class:?]

at net.minecraft.world.WorldServer.func_147456_g(WorldServer.java:331) ~[WorldServer.class:?]

at net.minecraft.world.WorldServer.tick(WorldServer.java:191) ~[WorldServer.class:?]

at net.minecraft.server.MinecraftServer.updateTimeLightAndEntities(MinecraftServer.java:692) ~[MinecraftServer.class:?]

... 4 more

[22:09:51] [server thread/ERROR]: This crash report has been saved to: E:\ModdingWorkspace\run\.\crash-reports\crash-2015-04-15_22.09.51-server.txt

[22:09:51] [server thread/INFO]: Stopping server

[22:09:51] [server thread/INFO]: Saving players

[22:09:51] [Client thread/INFO] [sTDOUT]: [net.minecraft.client.Minecraft:displayCrashReport:388]: ---- Minecraft Crash Report ----

// Why is it breaking

 

Time: 4/15/15 10:09 PM

Description: Exception ticking world

 

java.lang.NullPointerException: Exception ticking world

at net.minecraft.world.chunk.storage.ExtendedBlockStorage.getExtSkylightValue(ExtendedBlockStorage.java:164)

at net.minecraft.world.chunk.Chunk.getBlockLightValue(Chunk.java:824)

at net.minecraft.world.World.getFullBlockLightValue(World.java:857)

at net.minecraft.world.World.func_147467_a(World.java:3133)

at net.minecraft.world.WorldServer.func_147456_g(WorldServer.java:331)

at net.minecraft.world.WorldServer.tick(WorldServer.java:191)

at net.minecraft.server.MinecraftServer.updateTimeLightAndEntities(MinecraftServer.java:692)

at net.minecraft.server.MinecraftServer.tick(MinecraftServer.java:614)

at net.minecraft.server.integrated.IntegratedServer.tick(IntegratedServer.java:118)

at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:485)

at net.minecraft.server.MinecraftServer$2.run(MinecraftServer.java:752)

 

 

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

---------------------------------------------------------------------------------------

 

-- Head --

Stacktrace:

at net.minecraft.world.chunk.storage.ExtendedBlockStorage.getExtSkylightValue(ExtendedBlockStorage.java:164)

at net.minecraft.world.chunk.Chunk.getBlockLightValue(Chunk.java:824)

at net.minecraft.world.World.getFullBlockLightValue(World.java:857)

at net.minecraft.world.World.func_147467_a(World.java:3133)

at net.minecraft.world.WorldServer.func_147456_g(WorldServer.java:331)

at net.minecraft.world.WorldServer.tick(WorldServer.java:191)

 

 

So I have some more work to do to figure out how to surgically disable the light updates just during generation. There are a number of public chunk variables also involved so I've started playing around with changing them. One that I thought would work was to change the heightmap prior to generation, since it seems that if the heightmap and block set position don't have gap it wouldn't update lighting, but that didn't speed it up. So I'll keep looking.

 

But overall I guess my advice is that setBlock is slower the higher you do it, but up to a factor of 5.

The fastest way to do it would be to access the chunk's

extendedblockstorage

arrays directly.  Build the structure, then in a last-pass do a standard

setBlock()

somewhere (possibly several?) to update the lighting once, rather than after every block.

The fastest way to do it would be to access the chunk's

extendedblockstorage

arrays directly.  Build the structure, then in a last-pass do a standard

setBlock()

somewhere (possibly several?) to update the lighting once, rather than after every block.

 

Yeah, that seems like the next logical step. I'll try that.