线程池与工作队列

来源：互联网发布：js数据结构编辑：程序博客网时间：2024/05/16 08:56

线程池主要用来解决线程生命周期开销问题和资源不足问题。通过对多个任务重用线程，线程创建的开销就被分摊到了多个任务上了，而且由于在请求到达时线程已经存在，所以消除了线程创建所带来的延迟。这样，就可以立即为请求服务，使应用程序响应更快。另外，通过适当地调整线程池中的线程数目可以防止出现资源不足的情况。

线程池中的所有线程主动从工作队列中寻找需要执行的工作。线程池中的所有线程主动从工作队列中寻找需要执行的工作。

将多而小的任务由有限的线程池中几个线程来执行。

线程池与工作队列
线程池与工作队列
import java.util.*;
public class WorkQueue
{
   private final int nThreads;//线程池的大小
   private final PoolWorker[] threads;//用数组实现线程池
   private final LinkedList queue;//任务队列

  public WorkQueue(int nThreads){
     this.nThreads = nThreads;
     queue = new LinkedList();
     threads = new PoolWorker[nThreads];

      for (int i=0; i<nThreads; i++) {
         threads[i] = new PoolWorker();
         threads[i].start();//启动所有工作线程
      }
  }

  public void execute(Runnable r) {//执行任务
    synchronized(queue) {
            queue.addLast(r);
            queue.notify();
    }
  }

  private class PoolWorker extends Thread {//工作线程类
        public void run() {
               Runnable r;
               while (true) {
                    synchronized(queue) {
                      while (queue.isEmpty()) {//如果任务队列中没有任务，等待
                        try{
                          queue.wait();
                        }catch (InterruptedException ignored){}
                      }
                       r = (Runnable) queue.removeFirst();//有任务时，取出任务
                   }
                   try {
                       r.run();//执行任务
                   }catch (RuntimeException e) {
                      // You might want to log something here
                  }
              }
      }
   }

public static void main(String args[]){
      WorkQueue wq=new WorkQueue(10);//10个工作线程
      Mytask r[]=new Mytask[20];//20个任务

      for(int i=0;i<20;i++){
           r[i]=new Mytask();
           wq.execute(r[i]);
      }
}
}
class Mytask implements Runnable{//任务接口
         public void run(){
              String name=Thread.currentThread().getName();
              try{
                  Thread.sleep(100);//模拟任务执行的时间
              }catch(InterruptedException e){}
              System.out.println(name+" executed OK");
         }
  }
运行结果：

C:/java>java   WorkQueue
Thread-1 executed OK
Thread-2 executed OK
Thread-3 executed OK
Thread-4 executed OK
Thread-5 executed OK
Thread-6 executed OK
Thread-7 executed OK
Thread-8 executed OK
Thread-9 executed OK
Thread-10 executed OK
Thread-1 executed OK
Thread-2 executed OK
Thread-3 executed OK
Thread-4 executed OK
Thread-5 executed OK
Thread-6 executed OK
Thread-7 executed OK
Thread-8 executed OK
Thread-9 executed OK
Thread-10 executed OK