newFixedThreadPool.setCorePoolSize()不使用线程,创建可能是开销的新的theads

Question

newFixedThreadPool.setCorePoolSize()不使用线程,创建新的theads.

说明:我为size2创建了一个newFixedThreadPool,如果这个池的两个线程都忙,我使用setCorePoolSize()向这个池添加两个线程.在这个过程中它似乎没有重用线程或者可能正在终止一些线程并创建新的,我将用代码解释.

代码:(请参阅输出以了解)

public class IncreasePoolSize
{
    static ExecutorService service = null;
    public static void main(String[] args) throws JMSException, InterruptedException
    {
        int NoOfth = 2;
        int noOfTimesToInc = 0;
        System.out.println("Start");
        service = Executors.newFixedThreadPool(NoOfth);
        for (;;)
        {
            if ( ((ThreadPoolExecutor)service).getActiveCount() >= NoOfth )
            {
                if (noOfTimesToInc < 1)
                {
                    System.out.println("Increased Threads-" + (noOfTimesToInc + 1) + " time(s)");
                    NoOfth += 2;
                    System.out.println("NoOfTh-" + NoOfth);
                    ((ThreadPoolExecutor)service).setCorePoolSize(NoOfth);
                    System.out.println("Total no of theads after increasing-" + ((ThreadPoolExecutor)service).getCorePoolSize());
                    noOfTimesToInc++;
                }

            }
            else if ( ((ThreadPoolExecutor)service).getActiveCount() <= NoOfth)
            {
                service.execute(new ConcreteThread());
            }
        }
    }

}

class ConcreteThread implements Runnable
{
    public void run() 
    {
        try
        {
             System.out.println("Thread No-" + Thread.currentThread().getId());
             Thread.sleep(5000);
             System.out.println("Thread No-" + Thread.currentThread().getId() + " finished");
        }
        catch(Exception e)
        {
            e.printStackTrace();
        }
    }
}

---

在输出中看到一旦11号和12号线程开始工作,我将数字增加2,所以线程13和14开始工作,但在那之后,我总是创建新线程而不是使用线程11和12并重新使用线程13和14.

输出:(已在调试模式下运行)

Start
Thread No-11
Thread No-12
Increased Threads-1 time(s)
NoOfTh-4
Total no of theads after increasing-4
Thread No-13
Thread No-14
Thread No-11 finished
Thread No-12 finished
Thread No-13 finished
Thread No-14 finished
Thread No-15
Thread No-16
Thread No-13
Thread No-14
Thread No-15 finished
Thread No-16 finished
Thread No-13 finished
Thread No-14 finished
Thread No-17
Thread No-18
Thread No-13
Thread No-14
Thread No-17 finished
Thread No-18 finished
Thread No-13 finished
Thread No-14 finished
Thread No-19
Thread No-20
Thread No-13
Thread No-14
Thread No-19 finished
Thread No-20 finished
Thread No-13 finished
Thread No-14 finished
Thread No-21
Thread No-22
Thread No-13
Thread No-14
Thread No-21 finished
Thread No-22 finished
Thread No-13 finished
Thread No-14 finished
Thread No-23
Thread No-24
Thread No-13
Thread No-14

---

Answer 1

您的代码的一个问题是您设置核心池大小而不是最大池大小.一个newFixedThreadPool使用相同数量的核心和最大池大小,并且您稍微违反了该合同.

如果你添加:

service.setMaximumPoolSize(NoOfth);

设置核心池大小后,将按预期重复使用相同的4个线程.

注意:这实际上是一个报告的错误

ThreadPoolExecutor的构造函数,setMaximumPoolSize如果corePoolSize > maximumPoolSize但是setCorePoolSize没有抛出IllegalArgumentException .