package com.atlassian.plugin.osgi.factory;
   
   public class ConcurrentStateEngine {
       private final Object[] states;
       private volatile int index = 0;
   
       public ConcurrentStateEngine(Object... states) {
           this.states = states;
       }
  
      public void tryNextState(Object expected, Object next) {
          System.out.println("trying to move from " + expected + " to " + next + " but in " + states[index]);
          int old = indexOf(expected);
          int tries = 100;
          while (old != index && tries-- > 0) {
              try {
                  Thread.sleep(100);
              } catch (InterruptedException e) {
                  e.printStackTrace();  //To change body of catch statement use File | Settings | File Templates.
              }
          }
          if (tries <= 0) {
              throw new IllegalStateException("Timeout waiting for state");
          }
          state(next);
      }
  
      public void state(Object next) {
          index = indexOf(next);
          System.out.println("Moved to state " + next + " (" + index + ")");
      }
  
      private int indexOf(Object state) {
          for (int x = 0; x < states.length; x++) {
              if (states[x].equals(state)) {
                  return x;
              }
          }
          throw new IllegalStateException("Cannot find state " + state);
      }
  }