They block. On network I/O.
If enough tasks are submitted the server will eventually stall
out due to a sync load, as the worldgen threads will be
stalling on profile lookups.
== AT ==
public net.minecraft.server.level.ServerChunkCache mainThread
public net.minecraft.server.level.ServerLevel chunkSource
public org.bukkit.craftbukkit.inventory.CraftItemStack handle
public net.minecraft.server.level.ChunkMap getVisibleChunkIfPresent(J)Lnet/minecraft/server/level/ChunkHolder;
public net.minecraft.server.level.ServerChunkCache mainThreadProcessor
public net.minecraft.server.level.ServerChunkCache$MainThreadExecutor
public net.minecraft.world.level.chunk.LevelChunkSection states