ThreadPool线程池的关注点

Posted 2020-08-05 wade&luffy

 
public class TestThreadPool {  
    //线程池维护线程的最少数量  
    private static final int COREPOOLSIZE = 2;  
    //线程池维护线程的最大数量  
    private static final int MAXINUMPOOLSIZE = 5;  
    //线程池维护线程所允许的空闲时间  
    private static final long KEEPALIVETIME = 4;  
    //线程池维护线程所允许的空闲时间的单位  
    private static final TimeUnit UNIT = TimeUnit.SECONDS;  
    //线程池所使用的缓冲队列,这里队列大小为3  
    private static final BlockingQueue<Runnable> WORKQUEUE = new ArrayBlockingQueue<Runnable>(3);  
    //线程池对拒绝任务的处理策略：
　　//AbortPolicy为抛出异常；
　　//CallerRunsPolicy为重试添加当前的任务，他会自动重复调用execute()方法；
　　//DiscardOldestPolicy为抛弃旧的任务，
　　//DiscardPolicy为抛弃当前的任务  
    private static final AbortPolicy HANDLER = new ThreadPoolExecutor.AbortPolicy();  
 
    public static void main(String[] args) {  
        // TODO 初始化线程池  
        ThreadPoolExecutor threadPool = new ThreadPoolExecutor(COREPOOLSIZE, MAXINUMPOOLSIZE, KEEPALIVETIME, UNIT, WORKQUEUE, HANDLER);  
        for (int i = 1; i < 11; i++) {  
            String task = "[email protected]"+i;  
            System.out.println("put->"+task);  
            //一个任务通过 execute(Runnable)方法被添加到线程池，任务就是一个 Runnable类型的对象，任务的执行方法就是 Runnable类型对象的run()方法  
            //处理任务的优先级为：核心线程corePoolSize、任务队列workQueue、最大线程maximumPoolSize，如果三者都满了，使用handler处理被拒绝的任务  
            //设此时线程池中的数量为currentPoolSize,若currentPoolSize>corePoolSize,则创建新的线程执行被添加的任务,  
            //当corePoolSize+workQueue>currentPoolSize>=corePoolSize,新增任务被放入缓冲队列,  
            //当maximumPoolSize>currentPoolSize>=corePoolSize+workQueue,建新线程来处理被添加的任务,  
            //当currentPoolSize>=maximumPoolSize,通过 handler所指定的策略来处理新添加的任务  
            //本例中可以同时可以被处理的任务最多为maximumPoolSize+WORKQUEUE=8个，其中最多5个在线程中正在处理，3个在缓冲队列中等待被处理  
            //当currentPoolSize>corePoolSize时，如果某线程空闲时间超过keepAliveTime，线程将被终止。这样，线程池可以动态的调整池中的线程数  
            threadPool.execute(new ThreadPoolTask(task));  
            try {  
                Thread.sleep(1000);  
            } catch (InterruptedException e) {  
                // TODO Auto-generated catch block  
                e.printStackTrace();  
            }  
        }  
        threadPool.shutdown();//关闭主线程，但线程池会继续运行，直到所有任务执行完才会停止。若不调用该方法线程池会一直保持下去，以便随时添加新的任务  
    }  
}

 

public class ThreadPoolTask implements Runnable,Serializable{  

 
    private Object threadPoolTaskData;  
    private static int produceTaskSleepTime = 10000;  
 
    public ThreadPoolTask(Object threadPoolTaskData) {  
        super();  
        this.threadPoolTaskData = threadPoolTaskData;  
    }  
 
    public void run() {  
        // TODO Auto-generated method stub  
        System.out.println("start..."+threadPoolTaskData);  
        try {  
            //模拟线程正在执行任务  
            Thread.sleep(produceTaskSleepTime);  
        } catch (InterruptedException e) {  
            // TODO Auto-generated catch block  
            e.printStackTrace();  
        }  
        System.out.println("stop..."+threadPoolTaskData);  
        threadPoolTaskData = null;  
    }  
 
    public Object getTask(){  
        return this.threadPoolTaskData;  
    }  
//---------------
put->[email protected]
[email protected]1
put->[email protected]
[email protected]2
put->[email protected]
put->[email protected]
put->[email protected]
put->[email protected]  
[email protected]6  
put->[email protected]
[email protected]7
put->[email protected]  
[email protected]8  
put->[email protected]  
Exception in thread "main" java.util.concurrent.RejectedExecutionException  
    at java.util.concurrent.ThreadPoolExecutor$AbortPolicy.rejectedExecution(Unknown Source)  
    at java.util.concurrent.ThreadPoolExecutor.reject(Unknown Source)  
    at java.util.concurrent.ThreadPoolExecutor.execute(Unknown Source)  
    at cn.gaialine.threadpool.TestThreadPool.main(TestThreadPool.java:42)  
[email protected]1
[email protected]3
[email protected]2
[email protected]4
[email protected]6  
[email protected]5
[email protected]7
[email protected]8  
[email protected]3
[email protected]4
[email protected]5

 

从中可以看出task1和task2依次最先执行，这时候currentPoolSize=2达到了corePoolSize，task3、task4、task5被送入缓冲队列，达到了workQueue最大值3，task6、task7、task8开启新的线程开始执行，此时currentPoolSize=5达到了maximumPoolSize，task9、task10根据AbortPolicy策略抛出异常，不再执行task9和task10。10秒钟后task1、task2….依次执行完毕释放线程，开始执行队列里的task3、task4、task5，最后task3、4、5执行完毕，所有任务完成。

 

JDK根据ThreadPoolExecutor配置好的线程池 

// 固定工作线程数量的线程池  

ExecutorService executorService1 = Executors.newFixedThreadPool(3);  

// 一个可缓存的线程池  

ExecutorService executorService2 = Executors.newCachedThreadPool();  

// 单线程化的Executor  

ExecutorService executorService3 = Executors.newSingleThreadExecutor();  

// 支持定时的以及周期性的任务执行  

ExecutorService executorService4 = Executors.newScheduledThreadPool(3);