Java ForkJoinPool getActiveThreadCount() Method

The getActiveThreadCount() method of ForkJoinPool class is used to estimate the number of active threads. This estimation may include stealing threads or currently executing the task. It may overestimate the number of active threads.

Syntax:

Parameter:

No parameter is passed.

Returns:

Return the number of active threads.

Throw:

Does not throw Exception.

Example 1

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.RecursiveAction;
  class Task9 extends RecursiveAction {
     private long Load = 0;
 public Task9(long Load) {
         this.Load = Load;
    }
    @Override
    protected void compute() {
        //if work is above threshold, break tasks up into smaller tasks
            List<Task9> subtasks = new ArrayList<Task9>();
                    subtasks.addAll(createSubtasks());
            for(RecursiveAction subtask : subtasks){
                subtask.fork();
            } 
    }
    private List<Task9> createSubtasks() {
        List<Task9> subtasks =new ArrayList<Task9>();
     Task9 subtask1 = new Task9(this.Load / 2);
     Task9 subtask2 = new Task9(this.Load / 2);
      Task9 subtask3 = new Task9(this.Load / 2);
        subtasks.add(subtask1);
        subtasks.add(subtask2);
        subtasks.add(subtask3);
        return subtasks;
    }

}
public class JavaForkJoingetActivethreadcountExample1 {
   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);
      ForkJoinPool Pool = ForkJoinPool.commonPool();
      System.out.println(" Before invoking number of active thread   :" +Pool.getActiveThreadCount());
       Task9 t = new Task9(400);
       Pool.invoke(t); 
      System.out.println(" After invoking Numbers of active thread   :" +Pool.getActiveThreadCount());
      System.out.println("Common Pool Size   :" +Pool.getPoolSize());
   }  
}

Test it Now

Output:

numbers of core available in your processor:4
 Before invoking number of active thread   :0
 After invoking Numbers of active thread   :3
Common Pool Size   :3

Example 2

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.RecursiveAction;
 class Task extends RecursiveAction {
     private long Load = 0; 
 public Task(long Load) {
         this.Load = Load;
    }
    @Override
    protected void compute() {
        //if work is above threshold, break tasks up into smaller tasks
            List<Task> subtasks = new ArrayList<Task>();
                 subtasks.addAll(createSubtasks());
            for(RecursiveAction subtask : subtasks){
                subtask.fork();
            }
    }
    private List<Task> createSubtasks() {
        List<Task> subtasks =new ArrayList<Task>();
     Task subtask1 = new Task(this.Load / 2);
     Task subtask2 = new Task(this.Load / 2);
     Task subtask3 = new Task(this.Load / 2);
        subtasks.add(subtask1);
        subtasks.add(subtask2);
        subtasks.add(subtask3);
        return subtasks;
    }
}
public class JavaForkJoingetActivethreadcountExample2 {
   public static void main(final String[] arguments) throws InterruptedException
      {      
      ForkJoinPool Pool = new ForkJoinPool(10);
       System.out.println(" Before invoking number of active thread   :" +Pool.getActiveThreadCount());
       Task t = new Task(1000000);
       Pool.invoke(t);
       Pool.execute(t);
       System.out.println(" After invoking Numbers of active thread   :" +Pool.getActiveThreadCount());
      System.out.println("Common Pool Size   :" +Pool.getPoolSize());
   }  
}

Test it Now

Output:

Before invoking number of active thread   :0
 After invoking Numbers of active thread   :10
Common Pool Size   :10

Next TopicJava Forkjoinpool getAsyncMode Method

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