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This article mainly introduces "Java how to use thread factory to monitor thread pool", in daily operation, I believe many people in Java how to use thread factory to monitor thread pool problems have doubts, Xiaobian consulted all kinds of information, sorted out simple and easy to use operation methods, hope to answer "Java how to use thread factory to monitor thread pool" doubts helpful! Next, please follow the small series to learn together!

ThreadFactory

Where do the threads in the thread pool come from? ThreadFoctory

public interface ThreadFactory { Thread newThread(Runnable r);}

Threadfactory has an interface, when the thread pool needs to create threads will call this method, you can also customize the thread factory

public class ThreadfactoryText { public static void main(String[] args) { Runnable runnable=new Runnable() { @Override public void run() { int num=new Random().nextInt(10); System.out.println(Thread.currentThread().getId()+"--"+System.currentTimeMillis()+"--Sleep"+num); try { TimeUnit.SECONDS.sleep(num); } catch (InterruptedException e) { e.printStackTrace(); } } }; //Create thread pool Use custom thread factory Adopt default reject policy ExecutorService executorService=new ThreadPoolExecutor(5, 5, 0, TimeUnit.SECONDS, new SynchronousQueue(), new ThreadFactory() { @Override public Thread newThread(Runnable r) { Thread t=new Thread(r); t.setDaemon(true);//Set to daemon thread, when the main thread runs out, threads in the thread pool will also be released System.out.println("thread created"+t); return t; } }); //Submit five tasks for (int i = 0; i

< 5; i++) { executorService.submit(runnable); } }} 当线程提交超过五个任务时，线程池会默认抛出异常 监控线程池 ThreadPoolExcutor提供了一组方法用于监控线程池 int getActiveCount()//获得线程池只当前的获得线程数量long getCompletedTaskCount()//返回线程池完成任务数量int getCorePoolSize()//线程池中核心任务数量int getLargestPoolSize() //返回线程池中曾经达到线程的最大数int getMaximumPoolSize()//返回线程池的最大容量int getPoolSize()//返回线程大小BlockingQueue getQueue()//返回阻塞队列long getTaskCount()//返回线程池收到任务总数public class Text { public static void main(String[] args) throws InterruptedException { Runnable runnable = new Runnable() { @Override public void run() { System.out.println(Thread.currentThread().getId() + "线程开始执行--" + System.currentTimeMillis()); try { Thread.sleep(10000); } catch (InterruptedException e) { e.printStackTrace(); } } }; //创建线程池 使用默认线程工厂 有界队列 采用DiscardPolicy策略 ThreadPoolExecutor executorService = new ThreadPoolExecutor(2, 5, 0, TimeUnit.SECONDS, new ArrayBlockingQueue(5),Executors.defaultThreadFactory(),new ThreadPoolExecutor.DiscardPolicy()); //提交五个任务 for (int i = 0; i < 30; i++) { executorService.submit(runnable); System.out.println("当前线程核心线程数"+executorService.getCorePoolSize()+",最大线程数："+executorService.getMaximumPoolSize()+",当前线程池大小："+executorService.getPoolSize()+"活动线程数："+executorService.getActiveCount()+",收到任务："+executorService.getTaskCount()+"完成任务数："+executorService.getCompletedTaskCount()+"等待任务数："+executorService.getQueue().size()); TimeUnit.MILLISECONDS.sleep(500); } System.out.println("-------------------"); while (executorService.getActiveCount()>

=0)//继续对线程池进行检测 { System.out.println("当前线程核心线程数"+executorService.getCorePoolSize()+",最大线程数："+executorService.getMaximumPoolSize()+",当前线程池大小："+executorService.getPoolSize()+"活动线程数："+executorService.getActiveCount()+",收到任务："+executorService.getTaskCount()+"完成任务数："+executorService.getCompletedTaskCount()+"等待任务数："+executorService.getQueue().size()); Thread.sleep(1000);//每1秒检测一次 } }}

当线程池大小达到了核心线程数，线程会被放在等待队列。当线程池等待队列已满会开启新的线程。当当前线程大小达到最大线程数，等待队列也满了，再提交的话会执行DiscardPolicy策略，直接丢弃这个无法处理的任务，最后30个任务只剩下15个了。

原理如图：

扩展线程池

有时候需要对线程池进行扩展，如在监控每个任务开始和结束时间，或者自定义其他增强功能。

ThreadPoolExecutor线程池提供了两个方法：

protected void beforeExecute(Thread t, Runnable r) { }protected void afterExecute(Runnable r, Throwable t) { }

线程池执行某个任务前会执行beforeExecute()方法，执行后会调用afterExecute()方法

查看ThreadPoolExecutor源码，在该类中定义了一个内部类Worker，ThreadPoolExecutor线程池的工作线程就是Worker类的实例，Worker实例在执行时会调用beforeExecute与afterExecute方法。

public void run() { runWorker(this);}final void runWorker(Worker w) { try { beforeExecute(wt, task); try { task.run(); afterExecute(task, null); } catch (Throwable ex) { afterExecute(task, ex); throw ex; } } finally { task = null; w.completedTasks++; w.unlock(); } } }

部分代码已省略，线程执行前会调用beforeExecute，执行后会调用afterExecute方法。

扩展线程池示例package com;import java.util.concurrent.ExecutorService;import java.util.concurrent.LinkedBlockingDeque;import java.util.concurrent.ThreadPoolExecutor;import java.util.concurrent.TimeUnit;public class Text07 { public static void main(String[] args) { //定义扩展线程池 定义线程池类继承ThreadPoolExecutor，然后重写其他方法 ExecutorService threadPoolExecutor= new ThreadPoolExecutor(5,5,0, TimeUnit.SECONDS,new LinkedBlockingDeque()){ //在内部类重写开始方法 @Override protected void beforeExecute(Thread t, Runnable r) { System.out.println(t.getId()+"线程准备执行任务"+((Mytask)r).name); } //在内部类重写结束方法 @Override protected void afterExecute(Runnable r, Throwable t) { System.out.println(((Mytask)r).name+"执行完成"); } //线程池退出 @Override protected void terminated() { System.out.println("线程池退出"); } }; for (int i = 0; i < 5; i++) { Mytask mytask=new Mytask("Thread"+i); threadPoolExecutor.execute(mytask); } } private static class Mytask implements Runnable { private String name; public Mytask(String name) { this.name=name; } @Override public void run() { System.out.println(name+"正在被执行"+Thread.currentThread().getId()); try { Thread.sleep(1000);//模拟任务时长 } catch (InterruptedException e) { e.printStackTrace(); } } }}

优化线程池大小

线程池大小对系统性能有一定影响，过大或者过小都无法方法发挥系统最佳性能，不需要非常精确，只要避免极大或者极小就可以了，一般来说线程池大小大姚考虑CPU数量

线程池大小=CPU数量 * 目标CPU使用率*（1+等待时间与计算时间的比）

线程池死锁

如果线程池执行中，任务A在执行过程中提交了任务B，任务B添加到线程池中的等待队列，如果A的结束需要B的执行结果，而B线程需要等待A线程执行完毕，就可能会使其他所有工作线程都处于等待状态，待这些任务在阻塞队列中执行。线程池中没有可以对阻塞队列进行处理的线程，就会一直等待下去照成死锁。

适合给线程池提交相互独立的任务，而不是彼此依赖的任务，对于彼此依赖的任务，可以考虑分别提交给不同的线程池来处理。

线程池异常信息捕获import java.util.concurrent.ExecutorService;import java.util.concurrent.SynchronousQueue;import java.util.concurrent.ThreadPoolExecutor;import java.util.concurrent.TimeUnit;public class Text09 { public static void main(String[] args) { //创建线程池 ExecutorService executorService=new ThreadPoolExecutor(5,5,0, TimeUnit.SECONDS,new SynchronousQueue()); //向线程池中添加两个数相处计算的任务 for (int i = 0; i

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