Java:使用Executors创建和管理线程

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());

       for (int i = 0; i < 10; i++)

           daemonExec.execute(new MyThread(i));

       for (int i = 10; i < 20; i++)

           if (i == 10)

              maxPriorityExec.execute(new MyThread(i));

           else if (i == 11)

              minPriorityExec.execute(new MyThread(i));

           else

              defaultExec.execute(new MyThread(i));

    }

}

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)

Create Thread-5

Thread-5 run 1 time(s)

Thread-5 run 2 time(s)

Create Thread-6

Create Thread-7

Thread-7 run 1 time(s)

Thread-7 run 2 time(s)

Create Thread-8

Thread-8 run 1 time(s)

Thread-8 run 2 time(s)

Create Thread-9

Create Thread-10

Thread-10 run 1 time(s)

Thread-10 run 2 time(s)

Create Thread-11

Thread-9 run 1 time(s)

Thread-9 run 2 time(s)

Thread-6 run 1 time(s)

Thread-6 run 2 time(s)

Thread-3 run 1 time(s)

Thread-3 run 2 time(s)

Create Thread-12

Create Thread-13

Create Thread-14

Thread-12 run 1 time(s)

Thread-12 run 2 time(s)

Thread-13 run 1 time(s)

Thread-13 run 2 time(s)

Create Thread-15

Thread-15 run 1 time(s)

Thread-15 run 2 time(s)

Create Thread-16

Thread-16 run 1 time(s)

Thread-16 run 2 time(s)

Create Thread-17

Create Thread-18

Create Thread-19

Thread-14 run 1 time(s)

Thread-14 run 2 time(s)

Thread-17 run 1 time(s)

Thread-17 run 2 time(s)

Thread-18 run 1 time(s)

Thread-18 run 2 time(s)

Thread-19 run 1 time(s)

Thread-19 run 2 time(s)

Thread-11 run 1 time(s)

Thread-11 run 2 time(s)