Fixed #5414

core/src/mindustry/mod/ModClassLoader.java

@@ -4,7 +4,12 @@ import arc.struct.*;
 
 public class ModClassLoader extends ClassLoader{
     private Seq<ClassLoader> children = new Seq<>();
-    private volatile boolean inChild = false;
+    private ThreadLocal<Boolean> inChild = new ThreadLocal<>(){
+        @Override
+        protected Boolean initialValue(){
+            return Boolean.FALSE;
+        }
+    };
 
     public void addChild(ClassLoader child){
         children.add(child);
@@ -13,15 +18,15 @@ public class ModClassLoader extends ClassLoader{
     @Override
     protected Class<?> findClass(String name) throws ClassNotFoundException{
         //a child may try to delegate class loading to its parent, which is *this class loader* - do not let that happen
-        if(inChild){
-            inChild = false;
+        if(inChild.get()){
+            inChild.set(false);
             throw new ClassNotFoundException(name);
         }
 
         ClassNotFoundException last = null;
         int size = children.size;
 
-        inChild = true;
+        inChild.set(true);
         //if it doesn't exist in the main class loader, try all the children
         for(int i = 0; i < size; i++){
             try{
@@ -30,7 +35,7 @@ public class ModClassLoader extends ClassLoader{
                 last = e;
             }
         }
-        inChild = false;
+        inChild.set(false);
 
         throw (last == null ? new ClassNotFoundException(name) : last);
     }