Merge 1.19.4 into 1.20

Author: embeddedt

forge/src/main/java/org/embeddedt/modernfix/forge/mixin/bugfix/chunk_deadlock/ServerChunkCache_CurrentLoadingMixin.java

@@ -0,0 +1,57 @@
+package org.embeddedt.modernfix.forge.mixin.bugfix.chunk_deadlock;
+
+import net.minecraft.server.level.ChunkHolder;
+import net.minecraft.server.level.ServerChunkCache;
+import net.minecraft.world.level.ChunkPos;
+import net.minecraft.world.level.chunk.ChunkAccess;
+import net.minecraft.world.level.chunk.ChunkStatus;
+import net.minecraft.world.level.chunk.LevelChunk;
+import net.minecraftforge.fml.util.ObfuscationReflectionHelper;
+import org.jetbrains.annotations.Nullable;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.Shadow;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.Inject;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfoReturnable;
+
+import java.lang.invoke.MethodHandle;
+import java.lang.invoke.MethodHandles;
+import java.lang.reflect.Field;
+
+@Mixin(ServerChunkCache.class)
+public abstract class ServerChunkCache_CurrentLoadingMixin {
+    @Shadow @Nullable protected abstract ChunkHolder getVisibleChunkIfPresent(long l);
+
+    private static final MethodHandle CURRENTLY_LOADING;
+
+    static {
+        try {
+            Field currentlyLoadingField = ObfuscationReflectionHelper.findField(ChunkHolder.class, "currentlyLoading");
+            currentlyLoadingField.setAccessible(true);
+            CURRENTLY_LOADING = MethodHandles.lookup().unreflectGetter(currentlyLoadingField);
+        } catch(Exception e) {
+            throw new RuntimeException("Failed to get currentlyLoading field", e);
+        }
+    }
+
+    /**
+     * Check the currentlyLoading field before going to the future chain, as was done in 1.16. In 1.18 upstream seems
+     * to have only applied this to getChunkNow().
+     */
+    @Inject(method = "getChunk", at = @At(value = "INVOKE", target = "Lnet/minecraft/server/level/ServerChunkCache;getChunkFutureMainThread(IILnet/minecraft/world/level/chunk/ChunkStatus;Z)Ljava/util/concurrent/CompletableFuture;"), cancellable = true)
+    private void checkCurrentlyLoading(int chunkX, int chunkZ, ChunkStatus requiredStatus, boolean load, CallbackInfoReturnable<ChunkAccess> cir) {
+        long i = ChunkPos.asLong(chunkX, chunkZ);
+        ChunkHolder holder = this.getVisibleChunkIfPresent(i);
+        if(holder != null) {
+            LevelChunk c;
+            try {
+                c = (LevelChunk)CURRENTLY_LOADING.invokeExact(holder);
+            } catch(Throwable e) {
+                e.printStackTrace();
+                c = null;
+            }
+            if(c != null)
+                cir.setReturnValue(c);
+        }
+    }
+}