黑马程序员 java Executors

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java并发编程——Executors

　　Sun在java5中，对java线程的类库做了大量的扩展，其中线程池就是java5的新特征之一。除此之外，还有很多与多线程编程相关的内容。

　　线程池的思想是一种对象池的思想，开放一块内存空间，里面存放了众多（未死亡）的线程，池中线程执行调度由池管理器来处理。当有线程任务时，从池中取一个，执行完毕，对象归还给池。这样可以避免反复创建线程对象所带来的性能开销，节省了系统的资源。

　　在Java5之前，要实现一个线程池是相当有难度的，现在Java5为我们做好了一切，我们只需要按照提供的API来使用，即可享受线程池带来的极大便利。

　　Java5的线程池分好多种：固定尺寸的线程池、可变尺寸连接池等。

　　在使用线程池之前，必须知道如何去创建一个线程池，在Java5中，需要了解的是java.util.concurrent.Executors类的API，这个类提供大量创建连接池的静态方法，是必须掌握的。

　　一、固定大小的线程池

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

/**
*
* @author hxm
*
*/
public class TestThread {
public static void main(String args[]){
//创建一个可重用固定线程数的线程池
ExecutorService pool = Executors.newFixedThreadPool(4);

//创建一个使用单个 worker 线程的 Executor，以无界队列方式来运行该线程。
ExecutorService pool = Executors.newSingleThreadExecutor();
//创建实现了runnable接口的对象
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();
}
}
class MyThread extends Thread{

@Override
public void run(){
System.out.println(Thread.currentThread().getName()+" is running...");
}
}

 pool-1-thread-1 is running...

pool-1-thread-1 is running...

pool-1-thread-3 is running...

pool-1-thread-2 is running...

pool-1-thread-4 is running...

二、单任务线程池

import java.util.concurrent.Executors;

/**
*
* @author hxm
*
*/
public class TestThread {
public static void main(String args[]){
//创建一个使用单个 worker 线程的 Executor，以无界队列方式来运行该线程。
ExecutorService pool = Executors.newSingleThreadExecutor();
//创建实现了runnable接口的对象
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();
}
}
class MyThread extends Thread{

@Override
public void run(){
System.out.println(Thread.currentThread().getName()+" is running...");
}
}

pool-1-thread-1 is running...

pool-1-thread-1 is running...

pool-1-thread-1 is running...

pool-1-thread-1 is running...

pool-1-thread-1 is running...

对于以上两种连接池，大小都是固定的，当要加入的池的线程（或者任务）超过池最大尺寸时候，则进入此线程池需要排队等待。一旦池中有线程完毕，则排队等待的某个线程会入池执行。

三、 可变尺寸的线程池

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

/**
*
* @author hxm
*
*/
public class TestThread {
public static void main(String args[]){
//创建一个可根据需要创建新线程的线程池，但是在以前构造的线程可用时将重用它们。
ExecutorService pool = Executors.newCachedThreadPool();
//创建实现了runnable接口的对象
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();
}
}
class MyThread extends Thread{

@Override
public void run(){
System.out.println(Thread.currentThread().getName()+" is running...");
}
}

pool-1-thread-2 is running...

pool-1-thread-1 is running...

pool-1-thread-3 is running...

pool-1-thread-5 is running...

pool-1-thread-4 is running...

四、延迟连接池

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;

/**
*
* @author hxm
*
*/
public class TestThread {
public static void main(String args[]){
//创建一个线程池，它可安排在给定延迟后运行命令或者定期地执行
ScheduledExecutorService pool = Executors.newScheduledThreadPool(2);
//创建实现了runnable接口的对象
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);
//使用延迟执行风格的方法
pool.schedule(t4, 10, TimeUnit.MILLISECONDS);
pool.schedule(t5, 10, TimeUnit.MILLISECONDS);

//关闭线程池
pool.shutdown();
}
}
class MyThread extends Thread{

@Override
public void run(){
System.out.println(Thread.currentThread().getName()+" is running...");
}
}

pool-1-thread-2 is running...

pool-1-thread-2 is running...

pool-1-thread-1 is running...

pool-1-thread-2 is running...

pool-1-thread-1 is running...

五、单任务延迟连接池

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;

/**
*
* @author hxm
*
*/
public class TestThread {
public static void main(String args[]){
//创建一个线程池，它可安排在给定延迟后运行命令或者定期地执行
ScheduledExecutorService pool = Executors.newSingleThreadScheduledExecutor();
//创建实现了runnable接口的对象
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);
//使用延迟执行风格的方法
pool.schedule(t4, 10, TimeUnit.MILLISECONDS);
pool.schedule(t5, 10, TimeUnit.MILLISECONDS);

//关闭线程池
pool.shutdown();
}
}
class MyThread extends Thread{

@Override
public void run(){
System.out.println(Thread.currentThread().getName()+" is running...");
}
}

pool-1-thread-1 is running...

pool-1-thread-1 is running...

pool-1-thread-1 is running...

pool-1-thread-1 is running...

pool-1-thread-1 is running...

六、自定义线程池

代码

Code highlighting produced by Actipro CodeHighlighter (freeware)http://www.CodeHighlighter.com/--> 1 import java.util.concurrent.Arr
a25c
ayBlockingQueue;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;

/**
*
* @author hxm
*
*/
public class TestThread {
public static void main(String args[]){
//创建等待队列
BlockingQueue<Runnable> bqueue = new ArrayBlockingQueue<Runnable>(20);
//创建一个单线程执行程序，它可安排在给定延迟后运行命令或者定期地执行。
ThreadPoolExecutor pool = new ThreadPoolExecutor(2,3,2,TimeUnit.MILLISECONDS,bqueue);

//创建实现了runnable接口的对象
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();
}
}
class MyThread extends Thread{

@Override
public void run(){
System.out.println(Thread.currentThread().getName()+" is running...");
try {
Thread.sleep(100L);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}

pool-1-thread-2 is running...

pool-1-thread-1 is running...

pool-1-thread-2 is running...

pool-1-thread-1 is running...

pool-1-thread-2 is running...

里面的内容还有待在实际使用中更深入的理解消化！！！！

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