Executors

1. 类 Executors 
此类中提供的一些方法有： 
1.1 public static ExecutorService newCachedThreadPool() 
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。对于执行很多短期异步任务的程序而言，这些线程池通常可提高程序性能。 

1.2 public static ExecutorService newFixedThreadPool(int nThreads) 
创建一个可重用固定线程数的线程池，以共享的无界队列方式来运行这些线程。 

1.3 public static ExecutorService newSingleThreadExecutor() 
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。 

这三个方法都可以配合接口ThreadFactory的实例一起使用。并且返回一个ExecutorService接口的实例。 
2. 接口 ThreadFactory 
根据需要创建新线程的对象。使用线程工厂就无需再手工编写对 new Thread 的调用了，从而允许应用程序使用特殊的线程子类、属性等等。 
此接口最简单的实现就是： 

class SimpleThreadFactory implements ThreadFactory {
   public Thread newThread(Runnable r) {
     return new Thread(r);
   }
 }

3. 接口ExecutorService 
该接口提供了管理终止的方法。 
4.创建标准线程池启动线程 
4.1 提供一个简单的实现Runnable接口的线程 
MyThread.java 

package com.zj.concurrency.executors;

public class MyThread implements Runnable {
    private int count = 1, number;

    public MyThread(int num) {
       number = num;
       System.out.println("Create Thread-" + number);
    }

    public void run() {
       while (true) {
           System.out.println("Thread-" + number + " run " + count+" time(s)");
           if (++count == 3)
              return;
       }
    }
}

这个线程会打印出相应的创建和执行信息。 

4.2使用CachedThreadPool启动线程 
CachedThreadPool.java 

package com.zj.concurrency.executors;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class CachedThreadPool {
    public static void main(String[] args) {
       ExecutorService exec = Executors.newCachedThreadPool();
       for (int i = 0; i < 5; i++)
           exec.execute(new MyThread(i));
       exec.shutdown();
    }
}

结果： 
Create Thread-0 
Create Thread-1 
Create Thread-2 
Create Thread-3 
Thread-0 run 1 time(s) 
Thread-0 run 2 time(s) 
Thread-1 run 1 time(s) 
Thread-1 run 2 time(s) 
Thread-2 run 1 time(s) 
Thread-2 run 2 time(s) 
Create Thread-4 
Thread-4 run 1 time(s) 
Thread-4 run 2 time(s) 
Thread-3 run 1 time(s) 
Thread-3 run 2 time(s) 

4.3 使用FixedThreadPool启动线程 
FixedThreadPool.java 

package com.zj.concurrency.executors;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class FixedThreadPool {
    public static void main(String[] args) {
       ExecutorService exec = Executors.newFixedThreadPool(2);
       for (int i = 0; i < 5; i++)
           exec.execute(new MyThread(i));
       exec.shutdown();
    }
}

结果： 
Create Thread-0 
Create Thread-1 
Create Thread-2 
Create Thread-3 
Create Thread-4 
Thread-0 run 1 time(s) 
Thread-0 run 2 time(s) 
Thread-2 run 1 time(s) 
Thread-2 run 2 time(s) 
Thread-3 run 1 time(s) 
Thread-3 run 2 time(s) 
Thread-4 run 1 time(s) 
Thread-4 run 2 time(s) 
Thread-1 run 1 time(s) 
Thread-1 run 2 time(s) 

4.4 使用SingleThreadExecutor启动线程 
SingleThreadExecutor.java 

package com.zj.concurrency.executors;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class SingleThreadExecutor {
    public static void main(String[] args) {
       ExecutorService exec = Executors.newSingleThreadExecutor();
       for (int i = 0; i < 5; i++)
           exec.execute(new MyThread(i));
       exec.shutdown();
    }
}

结果： 
Create Thread-0 
Create Thread-1 
Create Thread-2 
Create Thread-3 
Create Thread-4 
Thread-0 run 1 time(s) 
Thread-0 run 2 time(s) 
Thread-1 run 1 time(s) 
Thread-1 run 2 time(s) 
Thread-2 run 1 time(s) 
Thread-2 run 2 time(s) 
Thread-3 run 1 time(s) 
Thread-3 run 2 time(s) 
Thread-4 run 1 time(s) 
Thread-4 run 2 time(s) 
5.配合ThreadFactory接口的使用 
我们试图给线程加入daemon和priority的属性设置。 
5.1设置后台线程属性 
DaemonThreadFactory.java 

package com.zj.concurrency.executors.factory;
import java.util.concurrent.ThreadFactory;

public class DaemonThreadFactory implements ThreadFactory {
    public Thread newThread(Runnable r) {
       Thread t = new Thread(r);
       t.setDaemon(true);
       return t;
    }
}

5.2 设置优先级属性 
最高优先级MaxPriorityThreadFactory.java 

package com.zj.concurrency.executors.factory;
import java.util.concurrent.ThreadFactory;

public class MaxPriorityThreadFactory implements ThreadFactory {
    public Thread newThread(Runnable r) {
       Thread t = new Thread(r);
       t.setPriority(Thread.MAX_PRIORITY);
       return t;
    }
}

最低优先级MinPriorityThreadFactory.java 

package com.zj.concurrency.executors.factory;
import java.util.concurrent.ThreadFactory;

public class MinPriorityThreadFactory implements ThreadFactory {
    public Thread newThread(Runnable r) {
       Thread t = new Thread(r);
       t.setPriority(Thread.MIN_PRIORITY);
       return t;
    }
}

5.3启动带有属性设置的线程 
ExecFromFactory.java 

package com.zj.concurrency.executors;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import com.zj.concurrency.executors.factory.DaemonThreadFactory;
import com.zj.concurrency.executors.factory.MaxPriorityThreadFactory;
import com.zj.concurrency.executors.factory.MinPriorityThreadFactory;

public class ExecFromFactory {
    public static void main(String[] args) throws Exception {
       ExecutorService defaultExec = Executors.newCachedThreadPool();
       ExecutorService daemonExec = Executors
              .newCachedThreadPool(new DaemonThreadFactory());
       ExecutorService maxPriorityExec = Executors
              .newCachedThreadPool(new MaxPriorityThreadFactory());
       ExecutorService minPriorityExec = Executors
              .newCachedThreadPool(new MinPriorityThreadFactory());
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