How to store Java Callable job in ConcurrentHashMap

Question

I am new to the Multithreading and here is a question: For a Callable interface, like:

public interface Callable<V> {
    public V call();
}

Now I need to implement a class with three method:

/* register some callable jobs with the signal key */
void register(int signal, Callable cb); 

/* unregister */
void unregister(int signal, Callable cb);

/* run all the jobs with the given signal */
void signal(int signal);

I am thinking the register and unregister function I will use a ConcurrentHashMap in java, some structure like :

ConcurrentHashMap<Integer, List<Callable>> 

Then here are my questions:

1. how to support the above three method? How to pass a Callable as a variable? The void signal(int signal) will run all the callable with the given signal key.
2. for Callable interface, need to implement the V call() function. How does this call() relate to the signal() method? Should signal call this call()?

Answer 1

You can create new iterface extends callable and add your custom method like getId.

 public interface  MyCallable  extends Callable<String> {
  public int getId();
}

-Create a implemented class which will implement your custom callable interface.

 public class CallableImpl implements Callable<String> {
       private Callable action;
       private int key;
     public CallableImpl (Callable action,int key){
          this.action=action;
          this.key=key;
        }
        @Override
        public String call() throws Exception {
          return  action.call();
        }
    public int getId(){
     return key;
}

-register(int signal, Callable cb) method will take the object of callable class and store in a hashmap.On call to void signal(int signal) it will collect all list of action from hashmap and submit to an executor.

ExecutorService executor = Executors.newFixedThreadPool(10);
void signal(int signal){
for(Callable c:actionList){
  //submit Callable tasks to be executed by thread pool
  Future<String> future = executor.submit(callable);
  //add Future to the list, we can get return value using Future
  list.add(future);
}
}