1.线程池优点: 1).减少创建和销毁线程的次数 2).可以根据系统的能力,调整线程池中线程的数目 3).减少切换线程的开销
2.实现自定义线程池 思路: 1)将线程池线程定义为守护线程(这样可以保证在线程池中的线程结束后自动退出,同时监视线程池) 2)创建一个工作队列保存线程(Runnable) 3)执行线程的类 4)定义线程池的状态参数 实现:
public class ThreadPool extends ThreadGroup { private boolean isClosed = false; //线程池是否关闭 private LinkedList<Runnable> workQueue; //工作队列 private static int threadPoolID; //线程池ID private int threadID; //工作线程的ID public ThreadPool(int poolSize){ super("ThreadPool-" + (threadPoolID++)); //ThreadGroup(String name),线程池名字 setDaemon(true); //设置为守护线程 workQueue = new LinkedList<Runnable>(); for(int i=0; i<poolSize; i++){ new WorkThread().start(); //启动线程 } } //加入任务 public synchronized void execute(Runnable task){ if(isClosed){ throw new IllegalStateException(); } if(task !=null){ workQueue.add(task); notify(); } } //获取线程任务 public synchronized Runnable getTask()throws Exception{ while(workQueue.size() == 0){ if(isClosed){ return null; } wait(); } return workQueue.removeFirst(); } //关闭线程池 public synchronized void close(){ if(!isClosed){ isClosed = true; workQueue.clear(); //清空所有工作线程 interrupt(); //中断所有工作线程(父类方法) } } //等待所有线程结束 public void join(){ synchronized (this){ isClosed = true; notifyAll(); } Thread[] threads = new Thread[activeCount()]; int count = enumerate(threads); for(int i=0; i<count; i++){ try { threads[i].join(); } catch (InterruptedException e) { e.printStackTrace(); } } } //工作线程类 private class WorkThread extends Thread{ public WorkThread(){ //加入线程组 super(ThreadPool.this,"WorkThread" + (threadID++)); } public void run(){ while(!isInterrupted()){ //isInterrupted(),继承于Thread类,判断线程是否被中断 Runnable task = null; try { task = getTask(); } catch (Exception e) { e.printStackTrace(); } if(task == null){ return; } task.run(); } } } }过程:在指定个数的线程中执行加入的任务,当队列为空但线程池未关闭时,在此等待,等待其他线程在有任务时唤醒或者线程中断关闭
测试类:
public class ThreadPoolTest { public static void main(String[] args) { if (args.length != 2) { System.out.println("please input args"); return; } int numTasks = Integer.parseInt(args[0]); int poolSize = Integer.parseInt(args[1]); //创建线程池 ThreadPool threadPool = new ThreadPool(poolSize); for (int i = 0; i < numTasks; i++) { threadPool.execute(createTask(i)); } threadPool.join(); } //执行的任务 private static Runnable createTask(final int taskID) { return new Runnable() { public void run() { System.out.println("Task" + taskID + "start"); try { Thread.sleep(1000); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("Task" + taskID + "end"); } }; } }