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Java:使用Executors创建和管理线程

本文于2082天之前发表,文中内容可能已经过时。

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);
}
}
  1. 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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