From a8d90955c7f8bd1ddc0950674ae064c98c044196 Mon Sep 17 00:00:00 2001
From: TheMode <themode@outlook.fr>
Date: Sun, 22 Aug 2021 09:57:39 +0200
Subject: [PATCH] Fix chunks being registered multiple times (weirdly only
 happen on Windows?)

Signed-off-by: TheMode <themode@outlook.fr>
---
 .../minestom/server/instance/InstanceContainer.java    | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/src/main/java/net/minestom/server/instance/InstanceContainer.java b/src/main/java/net/minestom/server/instance/InstanceContainer.java
index ae3089bd2..58d3db62d 100644
--- a/src/main/java/net/minestom/server/instance/InstanceContainer.java
+++ b/src/main/java/net/minestom/server/instance/InstanceContainer.java
@@ -49,6 +49,7 @@ public class InstanceContainer extends Instance {
     // (chunk index -> chunk) map, contains all the chunks in the instance
     // used as a monitor when access is required
     private final Long2ObjectMap<Chunk> chunks = new Long2ObjectOpenHashMap<>();
+    private final Long2ObjectMap<CompletableFuture<Chunk>> loadingChunks = new Long2ObjectOpenHashMap<>();
 
     private final Lock changingBlockLock = new ReentrantLock();
     private final Map<Point, Block> currentlyChangingBlocks = new HashMap<>();
@@ -259,6 +260,12 @@ public class InstanceContainer extends Instance {
 
     protected @NotNull CompletableFuture<@NotNull Chunk> retrieveChunk(int chunkX, int chunkZ) {
         CompletableFuture<Chunk> completableFuture = new CompletableFuture<>();
+        synchronized (loadingChunks) {
+            final long index = ChunkUtils.getChunkIndex(chunkX, chunkZ);
+            CompletableFuture<Chunk> loadingChunk = loadingChunks.get(index);
+            if (loadingChunk != null) return loadingChunk;
+            this.loadingChunks.put(index, completableFuture);
+        }
         final IChunkLoader loader = chunkLoader;
         final Runnable retriever = () -> loader.loadChunk(this, chunkX, chunkZ)
                 // create the chunk from scratch (with the generator) if the loader couldn't
@@ -267,6 +274,9 @@ public class InstanceContainer extends Instance {
                 .whenComplete((chunk, throwable) -> scheduleNextTick(instance -> {
                     cacheChunk(chunk);
                     EventDispatcher.call(new InstanceChunkLoadEvent(this, chunkX, chunkZ));
+                    synchronized (loadingChunks) {
+                        this.loadingChunks.remove(ChunkUtils.getChunkIndex(chunk));
+                    }
                     completableFuture.complete(chunk);
                 }));
         if (loader.supportsParallelLoading()) {