Java ForkJoinPool getStealCount() method

The getStealCount() method of ForkJoinPool class returns estimation of a number of tasks stolen from one thread by another after completing execution of all tasks in own queue. Steal count is high enough to keep thread busy but also it does not avoid overhead.

Syntax

Parameter

No parameter is passed.

Returns

This method returns the number of steals.

Example 1

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.RecursiveAction;

 class Work2 extends RecursiveAction {
     private long Load = 0;
 
 public Work2(long Load) {
         this.Load = Load;
    }
    @Override
    protected void compute() {
        //if work is above the threshold, break tasks up into smaller tasks
        
            List<Work2> subtasks = new ArrayList<Work2>();
          
                subtasks.addAll(createSubtasks());
            
            for(RecursiveAction subtask : subtasks){
                subtask.fork();
            } 
    }

    private List<Work2> createSubtasks() {
        List<Work2> subtasks =new ArrayList<Work2>();

     Work2 subtask1 = new Work2(this.Load / 2);
    
      
        subtasks.add(subtask1);
        
        return subtasks;
    }
}
public class JavaForkJoingetStealCountExample1 
 {
   public static void main(final String[] arguments) throws InterruptedException
      {      
      ForkJoinPool Pool = ForkJoinPool.commonPool();
      int i= Pool.getPoolSize();
      System.out.println("Steal Count  :" +Pool.getStealCount());
       Work2 t = new Work2(1000);
       Pool.invoke(t);
       Pool.execute(t);  
   }  
}

Test it Now

Output:

Steal Count  :0

Example 2

import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.RecursiveTask;
import java.util.concurrent.TimeUnit;

 class JavaForkJoingetStealCountExample2 {

   public static void main(final String[] arguments) throws InterruptedException
      {
      
      int proc = Runtime.getRuntime().availableProcessors();
      System.out.println("numbers of core available in your processor:"  +proc);
      
      int[] n = {20 , 23 , 5 ,6 ,7,8,23,12,56,1}; 
      ForkJoinPool Pool = new ForkJoinPool(proc);
      TestX t=new TestX(n,0,n.length);
      
     System.out.println(" Before Queued Submission  :" +Pool.getQueuedSubmissionCount());
      System.out.println("  is awaitQuiescent :" + Pool.awaitQuiescence(2, TimeUnit.SECONDS) );
     Pool.awaitTermination(3, TimeUnit.SECONDS);
   System.out.println(" Steal Count  :" +Pool.getStealCount());
      Integer r = Pool.invoke(t);
      System.out.println("Pool.invoke :" +r); 
   }  
}

   class TestX extends RecursiveTask<Integer> {
      int st;
      int end;
      int[] arr;

      TestX(int[] arr, int st, int end) {
         this.arr = arr;
         this.st  = st;
         this.end  = end;
      }

      protected Integer compute() {
         
         if(st - end <= 10) {
            int sum = 0;
            
            for(int i = st; i < end; ++i) 
               sum += arr[i];
              return sum;
         } else {	    	
            int mid = st + (end - st) / 2;
            TestX t1 = new TestX(arr, st, mid);
            TestX t2 = new TestX(arr, st, mid);
            invokeAll(t1 , t2);
             
            return (t1.join() + t2.join());
         }
      }
   }

Test it Now

Output:

numbers of core available in your processor:2
 Before Queued Submission  :0
  is awaitQuiescent :true
 Steal Count  :0
Pool.invoke :161

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