Android Handler as Post

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        safeFlag = false;
        if(onProcessFlag){
            synchronized (handler){
                handler.sendEmptyMessage(0);
            }
        }

    }

    @Override
    protected void onDestroy() {
        safeFlag = true;
        super.onDestroy();
    }

    static private final RingList<Runnable> runtimeProcess = new RingList<>(); //Source code: https://pastebin.com/Ci1rxFDr
    static private final TreeMap<Integer, Runnable> delayProcess = new TreeMap<>();
    static private int delayProcessCount = 1;
    static private boolean onProcessFlag = false;
    static private boolean safeFlag = false;

    static private Handler handler = new Handler(){
        @Override
        public void handleMessage(Message msg) {
            Runnable $;
            if(msg.what==0){
                if(safeFlag) return;
                onProcessFlag = false;
                do {
                    if(($=runtimeProcess.shift())!=null)
                        $.run();
                } while (runtimeProcess.size()!=0);
            } else {
                synchronized (delayProcess){
                    $=delayProcess.remove(msg.what);
                }
                if($!=null){
                    if(safeFlag){
                        MainActivity.post($);
                    } else {
                        $.run();
                    }
                }
            }
        }
    };

    static synchronized private void post(Runnable runnable){
        runtimeProcess.push(runnable);
        if(onProcessFlag) return;
        onProcessFlag = true;
        synchronized (handler){
            handler.sendEmptyMessage(0);
        }
    }

    static synchronized private void postDelay(Runnable runnable, long delay){
        int pc = delayProcessCount++;
        synchronized (delayProcess){
            delayProcess.put(pc, runnable);
        }
        synchronized (handler){
            handler.sendEmptyMessageDelayed(pc, delay);
        }
    }

    static private MainActivity self; {self = this;}

}