From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Aikar <aikar@aikar.co>
Date: Mon, 29 Jun 2020 04:00:07 -0400
Subject: [PATCH] Don't fire unleash/dismount events from worldgen threads

Mojang can trigger this during worldgen and tries to fire bukkit events.

diff --git a/src/main/java/net/minecraft/server/Entity.java b/src/main/java/net/minecraft/server/Entity.java
index 38887c1b7849926fab0a3b2db0e7b81388364172..2aa38528d78f2619317b96b1c944982b17f7160b 100644
--- a/src/main/java/net/minecraft/server/Entity.java
+++ b/src/main/java/net/minecraft/server/Entity.java
@@ -2117,7 +2117,7 @@ public abstract class Entity implements INamableTileEntity, ICommandListener, Ke
             // CraftBukkit start
             CraftEntity craft = (CraftEntity) entity.getBukkitEntity().getVehicle();
             Entity orig = craft == null ? null : craft.getHandle();
-            if (getBukkitEntity() instanceof Vehicle && entity.getBukkitEntity() instanceof LivingEntity) {
+            if (getBukkitEntity() instanceof Vehicle && entity.getBukkitEntity() instanceof LivingEntity && MCUtil.isMainThread()) { // Paper
                 VehicleExitEvent event = new VehicleExitEvent(
                         (Vehicle) getBukkitEntity(),
                         (LivingEntity) entity.getBukkitEntity(), !suppressCancellation // Paper
@@ -2132,7 +2132,7 @@ public abstract class Entity implements INamableTileEntity, ICommandListener, Ke
             // CraftBukkit end
             // Spigot start
             org.spigotmc.event.entity.EntityDismountEvent event = new org.spigotmc.event.entity.EntityDismountEvent(entity.getBukkitEntity(), this.getBukkitEntity(), !suppressCancellation); // Paper
-            Bukkit.getPluginManager().callEvent(event);
+            if (MCUtil.isMainThread()) Bukkit.getPluginManager().callEvent(event); // Paper
             if (event.isCancelled()) {
                 return false;
             }
diff --git a/src/main/java/net/minecraft/server/EntityInsentient.java b/src/main/java/net/minecraft/server/EntityInsentient.java
index 605bbf0174e60f795e445193a0284739ea452946..301f1ae8820df24d7c8453335abc1934aa7fae43 100644
--- a/src/main/java/net/minecraft/server/EntityInsentient.java
+++ b/src/main/java/net/minecraft/server/EntityInsentient.java
@@ -1339,7 +1339,7 @@ public abstract class EntityInsentient extends EntityLiving {
         boolean flag1 = super.a(entity, flag);
 
         if (flag1 && this.isLeashed()) {
-            this.world.getServer().getPluginManager().callEvent(new EntityUnleashEvent(this.getBukkitEntity(), UnleashReason.UNKNOWN)); // CraftBukkit
+            if (MCUtil.isMainThread()) this.world.getServer().getPluginManager().callEvent(new EntityUnleashEvent(this.getBukkitEntity(), UnleashReason.UNKNOWN)); // CraftBukkit // Paper
             this.unleash(true, true);
         }