Java并发编程中使用Executors类创建和管理线程的用法

1. 类 Executors

Executors类可以看做一个“工具类”。援引JDK1.6 API中的介绍:

  此包中所定义的 Executor、ExecutorService、ScheduledExecutorService、ThreadFactory 和 Callable 类的工厂和实用方法。此类支持以下各种方法:

(1)创建并返回设置有常用配置字符串的 ExecutorService 的方法。

(2)创建并返回设置有常用配置字符串的 ScheduledExecutorService 的方法。

(3)创建并返回“包装的”ExecutorService 方法,它通过使特定于实现的方法不可访问来禁用重新配置。

(4)创建并返回 ThreadFactory 的方法,它可将新创建的线程设置为已知的状态。

(5)创建并返回非闭包形式的 Callable 的方法,这样可将其用于需要 Callable 的执行方法中。

    通过这个类能够获得多种线程池的实例,例如可以调用newSingleThreadExecutor()获得单线程的ExecutorService,调 用newFixedThreadPool()获得固定大小线程池的ExecutorService,等等。拿到ExecutorService可以做的事情就比 较多了,最简单的是用它来执行Runnable对象,也可以执行一些实现了Callable<T>的对象。用Thread的start()方 法没有返回值,如果该线程执行的方法有返回值那用ExecutorService就再好不过了,可以选择submit()、invokeAll()或者 invokeAny(),根据具体情况选择合适的方法即可。

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)

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