Thread Pool

Thread pool: a collection of threads, the size of which is bounded.
Java provides thread pools through the Executor framework.
[Thoughts]: The following class implements part of a simple HTTP server。 If you don't use parallel computing, it will have poor ferformance becasue process request might frequently blocks on I/O.
Executors: 

• provide a layer of indirection between a client and the execution of a task; instead of client executing a task directly, an intermediate object executes the task; 
• Allow you to manage the execution of asynchronous tasks without having to explicitly manage the lifecycle of threads. 

newFixedthreadPool：Saves time, because do not need to pay for thread creation overhead for every single task.
newCachedThreadPool: create as many threads as it needs during the execution of a program and then will stop creating new threads as it recycles the old ones.

class TaskExecutionWebServer throws IOException{
  private static final int nthreads = 100;// control the number of threads launched. 
  private static final int serverport = 8080;
  private static final Executor exec = executors.newFixedthreadPool(nthreads);

  public static void main(Strings[] arg){
    ServerSocket serversocket = new ServerSocket(serverport);
    while(true){
      final Socket connection = serversocket.accept();
      Runnable task = new Runnable(){
        public void run(){
        Worker.handleRequest(connection);
        }
      };
    exec.execute(task);
  }
 }
}