Remove volatile from HandlerList to improve event performance

src/main/java/net/minecraft/server/AkarinUserCache.java

@@ -107,7 +107,7 @@ public class AkarinUserCache {
         Runnable find = () -> profileRepo.findProfilesByNames(new String[] { keyUsername }, Agent.MINECRAFT, callbackHandler);
         if (async) {
             MCUtil.scheduleAsyncTask(find);
-            return null; // TODO: future
+            return null;
         } else {
             find.run();
             return gameProfile[0];

src/main/java/net/minecraft/server/MCUtil.java

@@ -51,7 +51,7 @@ public final class MCUtil {
     }
 
     public static boolean isMainThread() {
-        return MinecraftServer.getServer().isMainThread();
+        return ThreadAssertion.isMainThread() && MinecraftServer.getServer().isMainThread(); // Akarin
     }
 
     private static class DelayedRunnable implements Runnable {