首页 > 代码库 > 线程池实例：使用Executors和ThreadPoolExecutor
线程池实例：使用Executors和ThreadPoolExecutor
线程池负责管理工作线程，包含一个等待执行的任务队列。线程池的任务队列是一个Runnable集合，工作线程负责从任务队列中取出并执行Runnable对象。
java.util.concurrent.executors 提供了 java.util.concurrent.executor 接口的一个Java实现，可以创建线程池。下面是一个简单示例：
首先创建一个Runable 类：
WorkerThread.java
package com.journaldev.threadpool; public class WorkerThread implements Runnable { private String command; public WorkerThread(String s){ this.command=s; } @Override public void run() { System.out.println(Thread.currentThread().getName()+" Start. Command = "+command); processCommand(); System.out.println(Thread.currentThread().getName()+" End."); } private void processCommand() { try { Thread.sleep(5000); } catch (InterruptedException e) { e.printStackTrace(); } } @Override public String toString(){ return this.command; }}
package com.journaldev.threadpool; public class WorkerThread implements Runnable { private String command; public WorkerThread(String s){ this.command=s; } @Override public void run() { System.out.println(Thread.currentThread().getName()+" Start. Command = "+command); processCommand(); System.out.println(Thread.currentThread().getName()+" End."); } private void processCommand() { try { Thread.sleep(5000); } catch (InterruptedException e) { e.printStackTrace(); } } @Override public String toString(){ return this.command; }}
下面是一个测试程序，从 Executors 框架中创建固定大小的线程池：
SimpleThreadPool.java
package com.journaldev.threadpool; import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors; public class SimpleThreadPool { public static void main(String[] args) { ExecutorService executor = Executors.newFixedThreadPool(5); for (int i = 0; i < 10; i++) { Runnable worker = new WorkerThread("" + i); executor.execute(worker); } executor.shutdown(); while (!executor.isTerminated()) { } System.out.println("Finished all threads"); } }
在上面的程序中，我们创建了包含5个工作线程的固定大小线程池。然后，我们向线程池提交10个任务。由于线程池的大小是5，因此首先会启动5个工作线程，其他任务将进行等待。一旦有任务结束，工作线程会从等待队列中挑选下一个任务并开始执行。
以上程序的输出结果如下：
pool-1-thread-2 Start. Command = 1pool-1-thread-4 Start. Command = 3pool-1-thread-1 Start. Command = 0pool-1-thread-3 Start. Command = 2pool-1-thread-5 Start. Command = 4pool-1-thread-4 End.pool-1-thread-5 End.pool-1-thread-1 End.pool-1-thread-3 End.pool-1-thread-3 Start. Command = 8pool-1-thread-2 End.pool-1-thread-2 Start. Command = 9pool-1-thread-1 Start. Command = 7pool-1-thread-5 Start. Command = 6pool-1-thread-4 Start. Command = 5pool-1-thread-2 End.pool-1-thread-4 End.pool-1-thread-3 End.pool-1-thread-5 End.pool-1-thread-1 End.Finished all threads
|
从输出结果看，线程池中有五个名为“pool-1-thread-1”…“pool-1-thread-5”的工作线程负责执行提交的任务。
Executors 类使用 ExecutorService 提供了一个 ThreadPoolExecutor 的简单实现，但 ThreadPoolExecutor 提供的功能远不止这些。我们可以指定创建 ThreadPoolExecutor 实例时活跃的线程数，并且可以限制线程池的大小，还可以创建自己的 RejectedExecutionHandler 实现来处理不适合放在工作队列里的任务。
下面是一个 RejectedExecutionHandler 接口的自定义实现：
RejectedExecutionHandlerImpl.java
package com.journaldev.threadpool; import java.util.concurrent.RejectedExecutionHandler;import java.util.concurrent.ThreadPoolExecutor; public class RejectedExecutionHandlerImpl implements RejectedExecutionHandler { @Override public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) { System.out.println(r.toString() + " is rejected"); } }
ThreadPoolExecutor 提供了一些方法，可以查看执行状态、线程池大小、活动线程数和任务数。所以，我通过一个监视线程在固定间隔输出执行信息。
MyMonitorThread.java
package com.journaldev.threadpool; import java.util.concurrent.ThreadPoolExecutor; public class MyMonitorThread implements Runnable{ private ThreadPoolExecutor executor; private int seconds; private boolean run=true; public MyMonitorThread(ThreadPoolExecutor executor, int delay) { this.executor = executor; this.seconds=delay; } public void shutdown(){ this.run=false; } @Override public void run() { while(run){ System.out.println( String.format("[monitor] [%d/%d] Active: %d, Completed: %d, Task: %d, isShutdown: %s, isTerminated: %s", this.executor.getPoolSize(), this.executor.getCorePoolSize(), this.executor.getActiveCount(), this.executor.getCompletedTaskCount(), this.executor.getTaskCount(), this.executor.isShutdown(), this.executor.isTerminated())); try { Thread.sleep(seconds*1000); } catch (InterruptedException e) { e.printStackTrace(); } } }}
|
下面是使用 ThreadPoolExecutor 的线程池实现示例：
WorkerPool.java
package com.journaldev.threadpool; import java.util.concurrent.ArrayBlockingQueue;import java.util.concurrent.Executors;import java.util.concurrent.ThreadFactory;import java.util.concurrent.ThreadPoolExecutor;import java.util.concurrent.TimeUnit; public class WorkerPool { public static void main(String args[]) throws InterruptedException{ //RejectedExecutionHandler implementation RejectedExecutionHandlerImpl rejectionHandler = new RejectedExecutionHandlerImpl(); //Get the ThreadFactory implementation to use ThreadFactory threadFactory = Executors.defaultThreadFactory(); //creating the ThreadPoolExecutor ThreadPoolExecutor executorPool = new ThreadPoolExecutor(2, 4, 10, TimeUnit.SECONDS, new ArrayBlockingQueue<Runnable>(2), threadFactory, rejectionHandler); //start the monitoring thread MyMonitorThread monitor = new MyMonitorThread(executorPool, 3); Thread monitorThread = new Thread(monitor); monitorThread.start(); //submit work to the thread pool for(int i=0; i<10; i++){ executorPool.execute(new WorkerThread("cmd"+i)); } Thread.sleep(30000); //shut down the pool executorPool.shutdown(); //shut down the monitor thread Thread.sleep(5000); monitor.shutdown(); }}
|
请注意：在初始化 ThreadPoolExecutor 时，初始线程池大小设为2、最大值设为4、工作队列大小设为2。所以，如果当前有4个任务正在运行而此时又有新任务提交，工作队列将只存储2个任务和其他任务将交由RejectedExecutionHandlerImpl 处理。
程序执行的结果如下，确认了上面的结论：
pool-1-thread-1 Start. Command = cmd0pool-1-thread-4 Start. Command = cmd5cmd6 is rejectedpool-1-thread-3 Start. Command = cmd4pool-1-thread-2 Start. Command = cmd1cmd7 is rejectedcmd8 is rejectedcmd9 is rejected[monitor] [0/2] Active: 4, Completed: 0, Task: 6, isShutdown: false, isTerminated: false[monitor] [4/2] Active: 4, Completed: 0, Task: 6, isShutdown: false, isTerminated: falsepool-1-thread-4 End.pool-1-thread-1 End.pool-1-thread-2 End.pool-1-thread-3 End.pool-1-thread-1 Start. Command = cmd3pool-1-thread-4 Start. Command = cmd2[monitor] [4/2] Active: 2, Completed: 4, Task: 6, isShutdown: false, isTerminated: false[monitor] [4/2] Active: 2, Completed: 4, Task: 6, isShutdown: false, isTerminated: falsepool-1-thread-1 End.pool-1-thread-4 End.[monitor] [4/2] Active: 0, Completed: 6, Task: 6, isShutdown: false, isTerminated: false[monitor] [2/2] Active: 0, Completed: 6, Task: 6, isShutdown: false, isTerminated: false[monitor] [2/2] Active: 0, Completed: 6, Task: 6, isShutdown: false, isTerminated: false[monitor] [2/2] Active: 0, Completed: 6, Task: 6, isShutdown: false, isTerminated: false[monitor] [2/2] Active: 0, Completed: 6, Task: 6, isShutdown: false, isTerminated: false[monitor] [2/2] Active: 0, Completed: 6, Task: 6, isShutdown: false, isTerminated: false[monitor] [0/2] Active: 0, Completed: 6, Task: 6, isShutdown: true, isTerminated: true[monitor] [0/2] Active: 0, Completed: 6, Task: 6, isShutdown: true, isTerminated: true
|
请注意活跃线程、已完成线程和任务完成总数的变化。我们可以调用 shutdown() 结束所有已提交任务并终止线程池。
如果希望延迟执行或定期运行任务，那么可以使用 ScheduledThreadPoolExecutor 类。要了解更多，请参见 Java Schedule Thread Pool Executor。
原文链接： journaldev 翻译： ImportNew.com - 彭秦进 译文链接： http://www.importnew.com/8542.html
线程池实例：使用Executors和ThreadPoolExecutor
声明：以上内容来自用户投稿及互联网公开渠道收集整理发布，本网站不拥有所有权，未作人工编辑处理，也不承担相关法律责任，若内容有误或涉及侵权可进行投诉： 投诉/举报 工作人员会在5个工作日内联系你，一经查实，本站将立刻删除涉嫌侵权内容。