java - Do i need to create new Callable object for each thread? -

here 2 options

1) create 1 callable , submit multiple times

callable<string> callable = new mycallable();         for(int i=0; i< 100; i++){            future<string> future = executor.submit(callable);             list.add(future);         }  

2) create multiple callables each thread

 for(int i=0; i< 100; i++){         future<string> future = executor.submit(new mycallable());         list.add(future);     }  

what best practice?

if mycallable thread-safe class can reuse same instance of it, otherwise, end race conditions , inconsistent results.

in other words, if mycallable tries hold state not synchronized properly, can't use same instance.

for example, below mycallable class, can't reuse same instance across multiple threads (i.e., can't share executor.submit(singleinstance)):

//non-thread safe callable implementation public class mycallable implements callable<string> {      private int i;      @override     public string call() throws exception {          i++; //race condition          system.out.println(i);          return string.valueof(i);     } } 

whereas if replace int atomicinteger, shown below, can reuse same instance:

//thread safe callable implementation public class mythreadsafecallable implements callable<string> {      private atomicinteger = new atomicinteger(0);      @override     public string call() throws exception {          int value = i.incrementandget();          system.out.println(value);          return string.valueof(value);     } } 

so, important point note here that, if wanted reuse same instance of callable, need ensure threadsafe. otherwise, need multiple callable instances submitted executorservice.