CallbackHandler to manage asyncs

app/src/main/java/com/topjohnwu/magisk/utils/CallbackHandler.java

@@ -0,0 +1,43 @@
+package com.topjohnwu.magisk.utils;
+
+import java.util.HashMap;
+import java.util.HashSet;
+
+public class CallbackHandler {
+
+    private static HashMap<Event, HashSet<EventListener>> listeners = new HashMap<>();
+
+    public static void register(Event event, EventListener listener) {
+        HashSet<EventListener> list = listeners.get(event);
+        if (list == null) {
+            list = new HashSet<>();
+            listeners.put(event, list);
+        }
+        list.add(listener);
+    }
+
+    public static void unRegister(Event event, EventListener listener) {
+        HashSet<EventListener> list = listeners.get(event);
+        if (list != null) {
+            list.remove(listener);
+        }
+    }
+
+    public static void triggerCallback(Event event) {
+        event.isTriggered = true;
+        HashSet<EventListener> list = listeners.get(event);
+        if (list != null) {
+            for (EventListener listener : list) {
+                listener.onTrigger(event);
+            }
+        }
+    }
+
+    public static class Event {
+        public boolean isTriggered = false;
+    }
+
+    public interface EventListener {
+        void onTrigger(Event event);
+    }
+}