From 1837f6c67798457cc3a9c16b8ba94d14dfcd8992 Mon Sep 17 00:00:00 2001
From: Spottedleaf <Spottedleaf@users.noreply.github.com>
Date: Tue, 25 Jul 2023 07:11:58 -0700
Subject: [PATCH] Prevent entity removals if the entity slices is receiving
 status updates

If an entity is removed while updating an entity slice, then the
iteration over the entity slice's entities could throw a cryptic
exception. Instead, it is better to prevent the entity removal
with a useful log message.

Fixes https://github.com/PaperMC/Paper/issues/9464
---
 .../server/0019-Rewrite-chunk-system.patch    | 32 +++++++++++++++----
 1 file changed, 25 insertions(+), 7 deletions(-)

diff --git a/patches/server/0019-Rewrite-chunk-system.patch b/patches/server/0019-Rewrite-chunk-system.patch
index 6bc5b1a2b0..0cc773795d 100644
--- a/patches/server/0019-Rewrite-chunk-system.patch
+++ b/patches/server/0019-Rewrite-chunk-system.patch
@@ -3742,10 +3742,10 @@ index 0000000000000000000000000000000000000000..924539d4ac50c70178ba220424ffacd6
 +}
 diff --git a/src/main/java/io/papermc/paper/chunk/system/entity/EntityLookup.java b/src/main/java/io/papermc/paper/chunk/system/entity/EntityLookup.java
 new file mode 100644
-index 0000000000000000000000000000000000000000..41791c7331c80d496cde4e3d1846a178bef0bbe3
+index 0000000000000000000000000000000000000000..ff7198a03ab0da79c98513f4a1507e854484f4c2
 --- /dev/null
 +++ b/src/main/java/io/papermc/paper/chunk/system/entity/EntityLookup.java
-@@ -0,0 +1,845 @@
+@@ -0,0 +1,859 @@
 +package io.papermc.paper.chunk.system.entity;
 +
 +import com.destroystokyo.paper.util.maplist.EntityList;
@@ -4144,6 +4144,17 @@ index 0000000000000000000000000000000000000000..41791c7331c80d496cde4e3d1846a178
 +        return true;
 +    }
 +
++    public boolean canRemoveEntity(final Entity entity) {
++        if (entity.updatingSectionStatus) {
++            return false;
++        }
++
++        final int sectionX = entity.sectionX;
++        final int sectionZ = entity.sectionZ;
++        final ChunkEntitySlices slices = this.getChunk(sectionX, sectionZ);
++        return slices == null || !slices.isPreventingStatusUpdates();
++    }
++
 +    private void removeEntity(final Entity entity) {
 +        final int sectionX = entity.sectionX;
 +        final int sectionY = entity.sectionY;
@@ -4157,6 +4168,9 @@ index 0000000000000000000000000000000000000000..41791c7331c80d496cde4e3d1846a178
 +        if (slices == null) {
 +            LOGGER.warn("Cannot remove entity " + entity + " from null entity slices (" + sectionX + "," + sectionZ + ")");
 +        } else {
++            if (slices.isPreventingStatusUpdates()) {
++                throw new IllegalStateException("Attempting to remove entity " + entity + " from entity slices (" + sectionX + "," + sectionZ + ") that is receiving status updates");
++            }
 +            if (!slices.removeEntity(entity, sectionY)) {
 +                LOGGER.warn("Failed to remove entity " + entity + " from entity slices (" + sectionX + "," + sectionZ + ")");
 +            }
@@ -16125,10 +16139,10 @@ index d59885ee9c8b29d5bac34dce0597e345e5358c77..f9063e2282f89e97a378f06822cde0a6
  }
 diff --git a/src/main/java/io/papermc/paper/world/ChunkEntitySlices.java b/src/main/java/io/papermc/paper/world/ChunkEntitySlices.java
 new file mode 100644
-index 0000000000000000000000000000000000000000..ce449b7b6f615f2c8240e4207f06d4e54ae0083e
+index 0000000000000000000000000000000000000000..7e8dc9e8f381abfdcce2746edc93122d623622d1
 --- /dev/null
 +++ b/src/main/java/io/papermc/paper/world/ChunkEntitySlices.java
-@@ -0,0 +1,602 @@
+@@ -0,0 +1,606 @@
 +package io.papermc.paper.world;
 +
 +import com.destroystokyo.paper.util.maplist.EntityList;
@@ -16307,6 +16321,10 @@ index 0000000000000000000000000000000000000000..ce449b7b6f615f2c8240e4207f06d4e5
 +        return ret;
 +    }
 +
++    public boolean isPreventingStatusUpdates() {
++        return this.preventStatusUpdates;
++    }
++
 +    public void stopPreventingStatusUpdates(final boolean prev) {
 +        this.preventStatusUpdates = prev;
 +    }
@@ -20636,7 +20654,7 @@ index 12e72ad737b1219fcdf88d344d41621d9fd5feec..e0bfeebeaac1aaea64bc07cdfdf7790e
                          if (flag1) {
                              ++this.converted;
 diff --git a/src/main/java/net/minecraft/world/entity/Entity.java b/src/main/java/net/minecraft/world/entity/Entity.java
-index bbc5ef297b740ab769e8c030e5af6f573259d953..88a84f453c38040933071ea61debcbb196ef10cf 100644
+index bbc5ef297b740ab769e8c030e5af6f573259d953..17841455d5afd60eca367591b06e22f69ee23ae4 100644
 --- a/src/main/java/net/minecraft/world/entity/Entity.java
 +++ b/src/main/java/net/minecraft/world/entity/Entity.java
 @@ -327,6 +327,58 @@ public abstract class Entity implements Nameable, EntityAccess, CommandSource {
@@ -20748,8 +20766,8 @@ index bbc5ef297b740ab769e8c030e5af6f573259d953..88a84f453c38040933071ea61debcbb1
      public final void setRemoved(Entity.RemovalReason reason) {
 +        // Paper start - rewrite chunk system
 +        io.papermc.paper.util.TickThread.ensureTickThread(this, "Cannot remove entity off-main");
-+        if (this.updatingSectionStatus) {
-+            LOGGER.warn("Entity " + this + " is currently prevented from being added/removed to world since it is processing section status updates", new Throwable());
++        if (!((ServerLevel)this.level).getEntityLookup().canRemoveEntity(this)) {
++            LOGGER.warn("Entity " + this + " is currently prevented from being removed from the world since it is processing section status updates", new Throwable());
 +            return;
 +        }
 +        // Paper end - rewrite chunk system