Using threadpoolExecutor

Question

Hi I want to use the threadpool provided in java. i.e Threadpoolexecutor.
The requirement is:
1. I need to have a corepool size(1)
2. I need to have Maxpoolsize(40)
3. I need to have a Queue without predefined capacity. I can use a LinkedBlockingQueue for this.
But the problem is, if i construct a threadpool,
ThreadPoolExecutor threadPool = new ThreadPoolExecutor(1,40,600, TimeUnit.SECONDS,new LinkedBlockingQueue<Runnable>());
No new threads are created until the queue is full. I.e the no more than corePoolSize threads will ever be created. (And the value of the maximumPoolSize therefore doesn't have any effect.). But what i need to have is everytime a task is submitted, it should create a thread until it reaches MaxpoolSize() and then it should start Queing requests.
Is there a way to do So.....

Answer 1

JoachimSauer ,
What you have made is both corepoolsize and maxpoolsizeequal, in which case its a fixedthreadpool.
I suggest you to go through javadoc for correct explanation on how threadpoolexecutor works.
Below attached is the code which exactly explains the problem.
As you can see, the first task is created until it is completed and all other tasks wait on it.
When you run the code, you will see that even though 50 tasks are pending, no new threads are created,
since the first thread is blocked on a sleep, and the queue is not full. hence eventhough the maxpoolsize is 40,
only one thread is created.
package testThreadPool;
public class sampleRunnable extends Thread{
     public void run()
          try {
               System.out.println("Inside : " + this.getName());
               Thread.sleep(Integer.MAX_VALUE);
               System.out.println("Finished : " + this.getName());
          } catch (InterruptedException e) {
               // TODO Auto-generated catch block
               e.printStackTrace();
package testThreadPool;
import java.util.Vector;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.ThreadPoolExecutor;
* @author hpke
public class testSampleRunnable {
      * @param args
     public static void main(String[] args) {
          // TODO Auto-generated method stub
          ThreadPoolExecutor threadPool = new ThreadPoolExecutor(1,40,600, TimeUnit.SECONDS,new LinkedBlockingQueue<Runnable>());
          for ( int i=0;i <50; i++){
               try {
                    Thread.sleep(1000);
               } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
               threadPool.execute(new sampleRunnable());
               Vector<String> threadPoolInfo = new Vector();
             threadPoolInfo.add("++ Thread Pool Info++");
             threadPoolInfo.add("getPoolSize() : " + threadPool.getPoolSize());
             threadPoolInfo.add("getActiveCount() : " + threadPool.getActiveCount());
             threadPoolInfo.add("getCompletedTaskCount() : " + threadPool.getCompletedTaskCount());
             threadPoolInfo.add("getCorePoolSize() : " + threadPool.getCorePoolSize());
             threadPoolInfo.add("getMaximumPoolSize() : " + threadPool.getMaximumPoolSize());
             threadPoolInfo.add("getLargestPoolSize() : " + threadPool.getLargestPoolSize());
             threadPoolInfo.add("getTaskCount() : " + threadPool.getTaskCount());
             threadPoolInfo.add("getKeepAliveTime() : " + threadPool.getKeepAliveTime(TimeUnit.SECONDS));
            String aa = new String();
            for ( int j=0;j< threadPoolInfo.size() ; j++)
                 aa += threadPoolInfo.elementAt(j) + "\n";
            System.out.println(aa);
}