code: public void start() {
      	if(this.isActive)
      		return;
      	
          if (clock == null) {
              throw new IllegalStateException("Clock is not set");
          }
  
          this.isActive = true;
          
          logger.info("Starting ");
          
          coreThread.activate();
          criticalThread.activate();
          for(int i=0;i<workerThreads.length;i++)
          	workerThreads[i].activate();
          
          for(int i=0;i<criticalWorkerThreads.length;i++)
          	criticalWorkerThreads[i].activate();        
          
          logger.info("Started ");
      }
docs: Starts scheduler.