java自带线程池和队列详细讲解

转载自：ThreadPoolExecutor使用和思考

一、简介

线程的使用在java中占有极其重要的地位，在jdk1.4极其之前的jdk版本中，关于线程池的使用是极其简陋的。在jdk1.5之后这一情况有了很大的改观。Jdk1.5之后加入了java.util.concurrent包，这个包中主要介绍java中线程以及线程池的使用，为我们在开发中处理线程的问题提供了非常大的帮助。

二、线程池

1、线程池的作用：

2、为什么要用线程池：

3、线程池比较重要的几个类：

4、常用线程池

Executors

Executors.newCachedThreadPool()

Executors.newFixedThreadPool(int)

Executors.newSingleThreadExecutor()

1）newSingleThreadExecutor

2）newFixedThreadPool

3）newCachedThreadPool

实例：

//MyThread.java
public classMyThread extends Thread {
@Override
publicvoid run() {
System.out.println(Thread.currentThread().getName() + "正在执行。。。");
}
}

//TestSingleThreadExecutor.java
public classTestSingleThreadExecutor {
publicstaticvoid main(String[] args) {
//创建一个可重用固定线程数的线程池
ExecutorService pool = Executors. newSingleThreadExecutor();
//创建实现了Runnable接口对象，Thread对象当然也实现了Runnable接口
Thread t1 = new MyThread();
Thread t2 = new MyThread();
Thread t3 = new MyThread();
Thread t4 = new MyThread();
Thread t5 = new MyThread();
//将线程放入池中进行执行
pool.execute(t1);
pool.execute(t2);
pool.execute(t3);
pool.execute(t4);
pool.execute(t5);
//关闭线程池
pool.shutdown();
}
}

pool-1-thread-1正在执行。。。
pool-1-thread-1正在执行。。。
pool-1-thread-1正在执行。。。
pool-1-thread-1正在执行。。。
pool-1-thread-1正在执行。。。

//TestFixedThreadPool.Java
public class TestFixedThreadPool {
publicstaticvoid main(String[] args) {
//创建一个可重用固定线程数的线程池
ExecutorService pool = Executors.newFixedThreadPool(2);
//创建实现了Runnable接口对象，Thread对象当然也实现了Runnable接口
Thread t1 = new MyThread();
Thread t2 = new MyThread();
Thread t3 = new MyThread();
Thread t4 = new MyThread();
Thread t5 = new MyThread();
//将线程放入池中进行执行
pool.execute(t1);
pool.execute(t2);
pool.execute(t3);
pool.execute(t4);
pool.execute(t5);
//关闭线程池
pool.shutdown();
}
}

pool-1-thread-1正在执行。。。
pool-1-thread-2正在执行。。。
pool-1-thread-1正在执行。。。
pool-1-thread-2正在执行。。。
pool-1-thread-1正在执行。。。

//TestCachedThreadPool.java
public class TestCachedThreadPool {
publicstaticvoid main(String[] args) {
//创建一个可重用固定线程数的线程池
ExecutorService pool = Executors.newCachedThreadPool();
//创建实现了Runnable接口对象，Thread对象当然也实现了Runnable接口
Thread t1 = new MyThread();
Thread t2 = new MyThread();
Thread t3 = new MyThread();
Thread t4 = new MyThread();
Thread t5 = new MyThread();
//将线程放入池中进行执行
pool.execute(t1);
pool.execute(t2);
pool.execute(t3);
pool.execute(t4);
pool.execute(t5);
//关闭线程池
pool.shutdown();
}
}

pool-1-thread-2正在执行。。。
pool-1-thread-4正在执行。。。
pool-1-thread-3正在执行。。。
pool-1-thread-1正在执行。。。
pool-1-thread-5正在执行。。。

//TestScheduledThreadPoolExecutor.java
public class TestScheduledThreadPoolExecutor {
publicstaticvoid main(String[] args) {
ScheduledThreadPoolExecutor exec = new ScheduledThreadPoolExecutor(1);
exec.scheduleAtFixedRate(new Runnable() {//每隔一段时间就触发异常
@Override
publicvoid run() {
//throw new RuntimeException();
System.out.println("================");
}
}, 1000, 5000, TimeUnit.MILLISECONDS);
exec.scheduleAtFixedRate(new Runnable() {//每隔一段时间打印系统时间，证明两者是互不影响的
@Override
publicvoid run() {
System.out.println(System.nanoTime());
}
}, 1000, 2000, TimeUnit.MILLISECONDS);
}
}

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三：ThreadPoolExecutor详解

1、ThreadPoolExecutor的完整构造方法的签名：

(int corePoolSize,int maximumPoolSize,long keepAliveTime,
TimeUnit unit,  BlockingQueue<Runnable> workQueue, ThreadFactory threadFactory,  RejectedExecutionHandler handler)

2、常用线程池的源码：

public static ExecutorService newFixedThreadPool(int nThreads) {
return new ThreadPoolExecutor(nThreads, nThreads,
0L, TimeUnit.MILLISECONDS,
new LinkedBlockingQueue<Runnable>());
}

public static ExecutorService newSingleThreadExecutor() {
return new FinalizableDelegatedExecutorService
(new ThreadPoolExecutor(1, 1,
0L, TimeUnit.MILLISECONDS,
new LinkedBlockingQueue<Runnable>()));
}

public static ExecutorService newCachedThreadPool() {
return new ThreadPoolExecutor(0, Integer.MAX_VALUE,
60L, TimeUnit.SECONDS,
new SynchronousQueue<Runnable>());
}

3、BlockingQueue<Runnable> workQueue详解

JDK描述引用：

排队有三种通用策略：

SynchronousQueue

LinkedBlockingQueue

ArrayBlockingQueue

实例：

new ThreadPoolExecutor(
2, 3, 30, TimeUnit.SECONDS,
new <span style="white-space: normal;">SynchronousQueue</span><Runnable>(),
new RecorderThreadFactory("CookieRecorderPool"),
new ThreadPoolExecutor.CallerRunsPolicy());

LinkedBlockingQueue

new ThreadPoolExecutor(
2, 4, 30, TimeUnit.SECONDS,
new ArrayBlockingQueue<Runnable>(2),
new RecorderThreadFactory("CookieRecorderPool"),
new ThreadPoolExecutor.CallerRunsPolicy());

总结：

4、keepAliveTime详解

5、RejectedExecutionHandler

public void rejectedExecution(Runnable r, ThreadPoolExecutor e) {
if (!e.isShutdown()) {
r.run();
}
}

public void rejectedExecution(Runnable r, ThreadPoolExecutor e) {
throw new RejectedExecutionException();
}

public void rejectedExecution(Runnable r, ThreadPoolExecutor e) {
}

public void rejectedExecution(Runnable r, ThreadPoolExecutor e) {
if (!e.isShutdown()) {
e.getQueue().poll();
e.execute(r);
}
}

总结：

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