CompletableFuture：java.util.concurrent.TimeoutException

Question

I am working on a use-case where 5 external tasks needs to be computed and then aggregated together. If all tasks do not complete within 3 secs, then return with completed tasks.

 private Set<Double> getPrices() throws ExecutionException, InterruptedException, TimeoutException {
    Set<Double> prices=new CopyOnWriteArraySet<>(); // Concurrent Set
    //5 independant Tasks
    CompletableFuture<Void> d1= CompletableFuture.runAsync(new Task("1", prices))
            .thenRunAsync(new Task("2", prices))
            .thenRunAsync(new Task("3", prices))
            .thenRunAsync(new Task("4", prices))
            .thenRunAsync(new Task("5", prices));
           d1.get(3,TimeUnit.SECONDS);
         return prices;
       }

The run method in class:Task calls external system to retrieve result. For simplicity, return a random price(1-00)

    class Task{
       private String id; //Task-ID            
       private Set<Double> prices;                                                                              
       public  Task(String id,Set<Double> prices){                              
         this.id=id;                                                         
         this.prices=prices;                                                   
     }             
      @Override                                
       public void run() {                      
         try {                                
           Thread.sleep(1500); //Adding delay to simulate external call
           double d =Math.random*100;//Calling external System         
           prices.add(d);             
       } catch (InterruptedException e) {   
           throw new RuntimeException(e);   
      }                                    
                             
    }  
   }   

When I call the getPrice method, get java.util.concurrent.TimeoutException

     public static void main(String args []) throws InterruptedException, 
      ExecutionException, TimeoutException {

   PriceComparatorAggregator p2=new PriceComparatorAggregator();
    outputPrices = p2.usingCompletableFuture();
    for(Double d:outputPrices)
        System.out.println(d);
    System.out.println("Complete..!!");  
    }                                 

Answer 1

You are running these tasks in a sequence (one task starts after the previous completes), it will take more than 3 seconds to run all of them.

I think you want to run them in parallel. This is one way you could do it:

    public static Set<Double> getPrices() throws Exception {
        Set<Double> prices = new CopyOnWriteArraySet<>(); // Concurrent Set

        CompletableFuture<Void>[] tasks = new CompletableFuture[5];
        for ( int i = 0; i < tasks.length; i++ ) {
            // Create a new task and run it
            tasks[i] = CompletableFuture.runAsync( new Task( String.valueOf( i + 1 ), prices ) );
        }
        // Wait for all the tasks to complete
        CompletableFuture.allOf( tasks ).get( 3, TimeUnit.SECONDS );
        return prices;
    }