From d12618af0fceb84da4d76e4d21b74c9aae9817ac Mon Sep 17 00:00:00 2001
From: Eoghanmc22 <Eoghanmc@icloud.com>
Date: Thu, 13 Aug 2020 18:50:57 -0400
Subject: [PATCH] Fix concurrent modify exception.

---
 .../net/minestom/server/thread/PerGroupChunkProvider.java | 6 ++----
 src/main/java/net/minestom/server/utils/MathUtils.java    | 8 ++++++++
 2 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/src/main/java/net/minestom/server/thread/PerGroupChunkProvider.java b/src/main/java/net/minestom/server/thread/PerGroupChunkProvider.java
index eba0a7696..ab53b1c6b 100644
--- a/src/main/java/net/minestom/server/thread/PerGroupChunkProvider.java
+++ b/src/main/java/net/minestom/server/thread/PerGroupChunkProvider.java
@@ -109,9 +109,7 @@ public class PerGroupChunkProvider extends ThreadProvider {
 
         ArrayList<Future<?>> futures = new ArrayList<>();
 
-        instanceInstanceMap.entrySet().forEach(entry -> {
-            final Instance instance = entry.getKey();
-            final Map<LongSet, Instance> instanceMap = entry.getValue();
+        instanceInstanceMap.forEach((instance, instanceMap) -> {
 
             // True if the instance ended its tick call
             AtomicBoolean instanceUpdated = new AtomicBoolean(false);
@@ -157,7 +155,7 @@ public class PerGroupChunkProvider extends ThreadProvider {
     }
 
     private Map<LongSet, Instance> getInstanceMap(Instance instance) {
-        return instanceInstanceMap.computeIfAbsent(instance, inst -> new HashMap<>());
+        return instanceInstanceMap.computeIfAbsent(instance, inst -> new ConcurrentHashMap<>());
     }
 
 }
diff --git a/src/main/java/net/minestom/server/utils/MathUtils.java b/src/main/java/net/minestom/server/utils/MathUtils.java
index fc00ee700..6d83fb761 100644
--- a/src/main/java/net/minestom/server/utils/MathUtils.java
+++ b/src/main/java/net/minestom/server/utils/MathUtils.java
@@ -70,4 +70,12 @@ public final class MathUtils {
     public static float setBetween(float number, float min, float max) {
         return number > max ? max : number < min ? min : number;
     }
+
+    public static int clamp(int value, int min, int max) {
+        if (value < min) {
+            return min;
+        } else {
+            return Math.min(value, max);
+        }
+    }
 }