Fix possible crashes on Threading

source/funkin/backend/utils/EngineUtil.hx

@@ -1,9 +1,16 @@
 package funkin.backend.utils;
 
+#if ALLOW_MULTITHREADING
+import sys.thread.Thread;
+#end
+
+#if !macro
 import funkin.backend.scripting.MultiThreadedScript;
 import funkin.backend.scripting.Script;
+#end
 
 final class EngineUtil {
+	#if !macro
 	/**
 	 * Starts a new multithreaded script.
 	 * This script will share all the variables with the current one, which means already existing callbacks will be replaced by new ones on conflict.
@@ -12,4 +19,32 @@ final class EngineUtil {
 	public static function startMultithreadedScript(path:String) {
 		return new MultiThreadedScript(path, Script.curScript);
 	}
+	#end
+
+	#if ALLOW_MULTITHREADING
+	public static var gameThreads:Array<Thread> = [];
+
+	private static var maxThreads:Int = 4;
+	private static var threadCycle:Int = 0;
+	private static var threadsInitialized:Bool = false;
+	#else
+	public static var gameThreads:Array<Dynamic> = [];
+	#end
+
+	/**
+	 * Execute a function asynchronously using existing threads when initialized with ALLOW_MULTITHREADING.
+	 * @param func Void -> Void
+	 */
+	public static function execAsync(func:Void->Void) {
+		#if ALLOW_MULTITHREADING
+		if (!threadsInitialized) {
+			threadsInitialized = true;
+			for (i in 0...maxThreads) gameThreads.push(Thread.createWithEventLoop(() -> Thread.current().events.promise()));
+		}
+		gameThreads[threadCycle].events.run(func);
+		if (++threadCycle >= maxThreads) threadCycle = 0;
+		#else
+		func();
+		#end
+	}
 }