线程池学习笔记

线程池的5中创建方式： 1、Single Thread Executor : 只有一个线程的线程池，因此所有提交的任务是顺序执行：

ExecutorService newSingleThreadExecutor = Executors.newSingleThreadExecutor();

2、Cached Thread Pool : 线程池里有很多线程需要同时执行，老的可用线程将被新的任务触发重新执行，如果线程超过60秒内没执行，那么将被终止并从池中删除：

ExecutorService newCachedThreadPool = Executors.newCachedThreadPool();

3、Fixed Thread Pool : 拥有固定线程数的线程池，如果没有任务执行，那么线程会一直等待，在构造函数中的参数4是线程池的大小，你可以随意设置，也可以和cpu的核数量保持一致，获取cpu的核数量int cpuNums = Runtime.getRuntime().availableProcessors()：

int cpuNums = Runtime.getRuntime().availableProcessors(); System.out.println(cpuNums); ExecutorService newFixedThreadPool = Executors.newFixedThreadPool(cpuNums);

4、Scheduled Thread Pool : 用来调度即将执行的任务的线程池，可能是不是直接执行, 每隔多久执行一次… 策略型的：

ScheduledExecutorService newScheduledThreadPool = Executors.newScheduledThreadPool(8);

5、Single Thread Scheduled Pool : 只有一个线程，用来调度任务在指定时间执行：

ScheduledExecutorService newSingleThreadScheduledExecutor = Executors.newSingleThreadScheduledExecutor();

*线程池的使用： 提交 Runnable ，任务完成后 Future 对象返回 null 调用excute,提交任务, 匿名Runable重写run方法, run方法里是业务逻辑

package cn.itcast_01_mythread.pool; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; public class ThreadPoolWithRunable { /** * 通过线程池执行线程 * @param args */ public static void main(String[] args) { //创建一个线程池 ExecutorService pool = Executors.newCachedThreadPool(); for(int i = 1; i < 5; i++){ pool.execute(new Runnable() { @Override public void run() { System.out.println("thread name: " + Thread.currentThread().getName()); try { Thread.sleep(1000); } catch (InterruptedException e) { e.printStackTrace(); } } }); } pool.shutdown(); } }

提交 Callable，该方法返回一个 Future 实例表示任务的状态 调用submit提交任务, 匿名Callable,重写call方法, 有返回值, 获取返回值会阻塞,一直要等到线程任务返回结果：

package cn.itcast_01_mythread.pool; import java.util.ArrayList; import java.util.List; import java.util.concurrent.Callable; import java.util.concurrent.ExecutionException; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.Future; /** * callable 跟runnable的区别： * runnable的run方法不会有任何返回结果，所以主线程无法获得任务线程的返回值 * * callable的call方法可以返回结果，但是主线程在获取时是被阻塞，需要等待任务线程返回才能拿到结果 * @author * */ public class ThreadPoolWithcallable { public static void main(String[] args) throws InterruptedException, ExecutionException { ExecutorService pool = Executors.newFixedThreadPool(4); for(int i = 0; i < 10; i++){ Future<String> submit = pool.submit(new Callable<String>(){ @Override public String call() throws Exception { //System.out.println("a"); Thread.sleep(5000); return "b--"+Thread.currentThread().getName(); } }); //从Future中get结果，这个方法是会被阻塞的，一直要等到线程任务返回结果 System.out.println(submit.get()); } pool.shutdown(); } }

TaskCallable：

package cn.itcast_01_mythread.pool; import java.util.Random; import java.util.concurrent.Callable; public class TaskCallable implements Callable<String>{ private int s; Random r = new Random(); public TaskCallable(int s){ this.s = s; } @Override public String call() throws Exception { String name = Thread.currentThread().getName(); long currentTimeMillis = System.currentTimeMillis(); System.out.println(name+" 启动时间：" + currentTimeMillis/1000); int rint = r.nextInt(3); try { Thread.sleep(rint*1000); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println(name + " is working..."+s); return s+""; } }

TaskRunnable：

package cn.itcast_01_mythread.pool; import java.util.Random; public class TaskRunnable implements Runnable{ private int s; public TaskRunnable(int s){ this.s = s; } Random r = new Random(); @Override public void run() { String name = Thread.currentThread().getName(); long currentTimeMillis = System.currentTimeMillis(); System.out.println(name+" 启动时间：" + currentTimeMillis/1000); int rint = r.nextInt(3); try { Thread.sleep(rint*1000); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println(name + " is working..."+s); } }

TestPool：

package cn.itcast_01_mythread.pool; import java.util.ArrayList; import java.util.HashMap; import java.util.Random; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.Future; import java.util.concurrent.ScheduledExecutorService; import java.util.concurrent.TimeUnit; import com.sun.corba.se.impl.encoding.OSFCodeSetRegistry.Entry; public class TestPool { public static void main(String[] args) throws Exception { Future<?> submit = null; Random random = new Random(); //创建固定数量线程池 // ExecutorService exec = Executors.newFixedThreadPool(4); //创建调度线程池 ScheduledExecutorService exec = Executors.newScheduledThreadPool(4); //用来记录各线程的返回结果 ArrayList<Future<?>> results = new ArrayList<Future<?>>(); for (int i = 0; i < 10; i++) { //fixedPool提交线程，runnable无返回值，callable有返回值 /*submit = exec.submit(new TaskRunnable(i));*/ /*submit = exec.submit(new TaskCallable(i));*/ //对于schedulerPool来说，调用submit提交任务时，跟普通pool效果一致 /*submit = exec.submit(new TaskCallable(i));*/ //对于schedulerPool来说，调用schedule提交任务时，则可按延迟，按间隔时长来调度线程的运行 submit = exec.schedule(new TaskCallable(i), random.nextInt(10), TimeUnit.SECONDS); //存储线程执行结果 results.add(submit); } //打印结果 for(Future f: results){ boolean done = f.isDone(); System.out.println(done?"已完成":"未完成"); //从结果的打印顺序可以看到，即使未完成，也会阻塞等待 System.out.println("线程返回future结果： " + f.get()); } exec.shutdown(); } }