PaperMC/patches/server/0871-Fix-swamp-hut-cat-generation-deadlock.patch

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Spottedleaf <Spottedleaf@users.noreply.github.com>
Date: Sat, 12 Mar 2022 06:31:13 -0800
Subject: [PATCH] Fix swamp hut cat generation deadlock

The worldgen thread will attempt to get structure references
via the world's getChunkAt method, which is fine if the gen is
not cancelled - but if the chunk was unloaded, the call will block
indefinitely. Instead of using the world state, we use the already
supplied generatoraccess which will always have the chunk available.

diff --git a/src/main/java/net/minecraft/world/entity/animal/Cat.java b/src/main/java/net/minecraft/world/entity/animal/Cat.java
index 5f7c394f9cc178c9cb06c90b91296b979d61239b..e4eac546836b73b5e9c8fd68ca0d32c01148313e 100644
--- a/src/main/java/net/minecraft/world/entity/animal/Cat.java
+++ b/src/main/java/net/minecraft/world/entity/animal/Cat.java
@@ -392,7 +392,7 @@ public class Cat extends TamableAnimal {
             Registry<ConfiguredStructureFeature<?, ?>> iregistry = worldserver1.registryAccess().registryOrThrow(Registry.CONFIGURED_STRUCTURE_FEATURE_REGISTRY);
 
             if (ChunkGenerator.allConfigurations(iregistry, StructureFeature.SWAMP_HUT).anyMatch((structurefeature) -> {
-                return worldserver1.structureFeatureManager().getStructureWithPieceAt(this.blockPosition(), structurefeature).isValid();
+                return worldserver1.structureFeatureManager().getStructureWithPieceAt(this.blockPosition(), structurefeature, world).isValid(); // Paper - fix deadlock
             })) {
                 this.setCatType(10);
                 this.setPersistenceRequired();
diff --git a/src/main/java/net/minecraft/world/level/StructureFeatureManager.java b/src/main/java/net/minecraft/world/level/StructureFeatureManager.java
index 81bb2235bec095b9e5fa7b41dfd12c6b06b4bdf5..fa6eaf7041b6a8b17c64322307839dbd358ad3ab 100644
--- a/src/main/java/net/minecraft/world/level/StructureFeatureManager.java
+++ b/src/main/java/net/minecraft/world/level/StructureFeatureManager.java
@@ -58,7 +58,12 @@ public class StructureFeatureManager {
     }
 
     public List<StructureStart> startsForFeature(SectionPos sectionPos, ConfiguredStructureFeature<?, ?> configuredStructureFeature) {
-        LongSet longSet = this.level.getChunk(sectionPos.x(), sectionPos.z(), ChunkStatus.STRUCTURE_REFERENCES).getReferencesForFeature(configuredStructureFeature);
+        // Paper start - add world option
+        return this.startsForFeature(sectionPos, configuredStructureFeature, (ServerLevelAccessor)null);
+    }
+    public List<StructureStart> startsForFeature(SectionPos sectionPos, ConfiguredStructureFeature<?, ?> configuredStructureFeature, ServerLevelAccessor world) {
+        LongSet longSet = (world == null ? this.level : world).getChunk(sectionPos.x(), sectionPos.z(), ChunkStatus.STRUCTURE_REFERENCES).getReferencesForFeature(configuredStructureFeature);
+        // Paper end - add world option
         Builder<StructureStart> builder = ImmutableList.builder();
         this.fillStartsForFeature(configuredStructureFeature, longSet, builder::add);
         return builder.build();
@@ -108,7 +113,12 @@ public class StructureFeatureManager {
     }
 
     public StructureStart getStructureWithPieceAt(BlockPos pos, ConfiguredStructureFeature<?, ?> configuredStructureFeature) {
-        for(StructureStart structureStart : this.startsForFeature(SectionPos.of(pos), configuredStructureFeature)) {
+        // Paper start - add world option
+        return this.getStructureWithPieceAt(pos, configuredStructureFeature, (ServerLevelAccessor)null);
+    }
+    public StructureStart getStructureWithPieceAt(BlockPos pos, ConfiguredStructureFeature<?, ?> configuredStructureFeature, ServerLevelAccessor world) {
+        // Paper end - add world option
+        for(StructureStart structureStart : this.startsForFeature(SectionPos.of(pos), configuredStructureFeature, world)) { // Paper - add world option
             if (this.structureHasPieceAt(pos, structureStart)) {
                 return structureStart;
             }