[PHP知识库]验证线程池扩展能力的测试方法的问题

java并发编程实战中第12章 12.1.3中验证线程池扩展能力的测试方法：

原例中有个bug：

代码中没有给newFixedThreadPool()传递threadFactory对象，所以怎么运行threadFactory.numCreated.get()都是0.

正确代码（可直接运行）：

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.atomic.AtomicInteger;

public class TestingThreadFactory implements ThreadFactory{
    public final AtomicInteger numCreated = new AtomicInteger();
    private final ThreadFactory factory = Executors.defaultThreadFactory();

    @Override
    public Thread newThread(Runnable r) {
        numCreated.incrementAndGet();
        return factory.newThread(r);
    }

    public static void main(String[] args) throws Exception {
        TestingThreadFactory threadFactory = new TestingThreadFactory();
        int MAX_SIZE = 10;
        ExecutorService exec = Executors.newFixedThreadPool(MAX_SIZE,threadFactory);

        for (int i = 0; i < 10 * MAX_SIZE; i++) {
            exec.execute(new Runnable() {
                @Override
                public void run() {
                    try {
                        Thread.sleep(Long.MAX_VALUE);
                    } catch (InterruptedException e) {
                        Thread.currentThread().interrupt();
                    }
                }
            });
        }

        for (int i = 0; i < 20 && threadFactory.numCreated.get() < MAX_SIZE; i++) {
            Thread.sleep(100);
        }
        System.out.println(threadFactory.numCreated.get());
        exec.shutdown();
    }
}

因为newFixedThreadPool是定长线程池，不能扩展，所以如果任务数小于MAX_SIZE，那么只会创建任务数量个线程，如果任务数大于MAX_SIZE，那么最多创建MAX_SIZE个线程。

最后i < 20 && threadFactory.numCreated.get() < MAX_SIZE是为了保证线程池中的已经有足够数量的任务执行了execute(或运行中或等待中)，要求2秒后停止等待，或者当运行中的线程数量超过了MAX_SIZE，表明当前线程池有扩展的能力，所以也会停止等待，继续执行。

参考：
验证线程池扩展能力的测试方法_iCheetor-CSDN博客