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Java : Thread Pool

Tutorial by:Arena Buocel      Date: 2016-05-04 05:22:48

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Java Thread pool represents a group of worker threads that are waiting for the job and reuse many times.

In case of thread pool, a group of fixed size threads are created. A thread from the thread pool is pulled out and assigned a job by the service provider. After completion of the job, thread is contained in the thread pool again.


Advantage of Java Thread Pool

Better performance It saves time because there is no need to create new thread.


Real time usage

It is used in Servlet and JSP where container creates a thread pool to process the request.


Example of Java Thread Pool

Let's see a simple example of java thread pool using ExecutorService and Executors.

File: WorkerThread.java

 
  1. import java.util.concurrent.ExecutorService;  
  2. import java.util.concurrent.Executors;  
  3. class WorkerThread implements Runnable {  
  4.     private String message;  
  5.     public WorkerThread(String s){  
  6.         this.message=s;  
  7.     }  
  8.      public void run() {  
  9.         System.out.println(Thread.currentThread().getName()+" (Start) message = "+message);  
  10.         processmessage();//call processmessage method that sleeps the thread for 2 seconds  
  11.         System.out.println(Thread.currentThread().getName()+" (End)");//prints thread name  
  12.     }  
  13.     private void processmessage() {  
  14.         try {  Thread.sleep(2000);  } catch (InterruptedException e) { e.printStackTrace(); }  
  15.     }  
  16. }  

File: JavaThreadPoolExample.java

 
  1. public class TestThreadPool {  
  2.      public static void main(String[] args) {  
  3.         ExecutorService executor = Executors.newFixedThreadPool(5);//creating a pool of 5 threads  
  4.         for (int i = 0; i < 10; i++) {  
  5.             Runnable worker = new WorkerThread("" + i);  
  6.             executor.execute(worker);//calling execute method of ExecutorService  
  7.           }  
  8.         executor.shutdown();  
  9.         while (!executor.isTerminated()) {   }  
  10.   
  11.         System.out.println("Finished all threads");  
  12.     }  
  13.  }  

Output:

pool-1-thread-1 (Start) message = 0
pool-1-thread-2 (Start) message = 1
pool-1-thread-3 (Start) message = 2
pool-1-thread-5 (Start) message = 4
pool-1-thread-4 (Start) message = 3
pool-1-thread-2 (End)
pool-1-thread-2 (Start) message = 5
pool-1-thread-1 (End)
pool-1-thread-1 (Start) message = 6
pool-1-thread-3 (End)
pool-1-thread-3 (Start) message = 7
pool-1-thread-4 (End)
pool-1-thread-4 (Start) message = 8
pool-1-thread-5 (End)
pool-1-thread-5 (Start) message = 9
pool-1-thread-2 (End)
pool-1-thread-1 (End)
pool-1-thread-4 (End)
pool-1-thread-3 (End)
pool-1-thread-5 (End)
Finished all threads

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