java - Avoiding a possible concurrency issue with a LIST being returned -

here sequence bother me begging standard remedy concurrency issue

1. create list object (lst)
2. initiate multple threads (updater threads)
3. send lst each updater threads update (add) it.
4. wait defined time (t1) let updater threads proceed updates.
5. after t1 time expired, return lst application (consumer-app) isn't in our control.
6. when return it, updater threads may still updating lst.
7. consumer-app doesn't know whether list still being updating in background updater threads.
8. consumer-app list operations (add/remove) on lst.

problem : lead concurrency issue.

how tackle this?

how stop updating threads after t1 effectively? or there standard way deal on this? synchronizedlist (collections.synchronizedlist(new arraylist())) in this?

edit : i'm aware of copyonwritearraylist also. i'm focusing on simple arraylist on this

you use executor service create , terminate threads, along copyonwritearraylist address concurrency.

 private copyonwritearraylist<someobject> somearraylist = new copyonwritearraylist<someobject>(); 

...

 class nodestatusthread implements runnable {          private executorservice updaterthreadexecutor = null;         private int numthrd = 20; //threads          private int timeout = 10; // ten-seconds           @override         public void run() {             (int i=0;i<numthrd; i++ ) {                 updaterthreadexecutor.execute(new updaterthread());             }             updaterthreadexecutor.shutdown();               try{                 //wait thread completion                 if(!updaterthreadexecutor.awaittermination(timeout, timeunit.seconds)){  //return false timeout surpassed                     updaterthreadexecutor.shutdownnow(); //forces thread termination                 }             }catch(interruptedexception e){                 updaterthreadexecutor.shutdownnow();             }          }  } 

...

 class updaterthread implements runnable {       @override     public void run() {         omearraylist.add(someobject);          somearraylist.remove(someobject);     }  }