测试特性

1. 核心线程大小为n，有界队列为m,当向线程池提交n+m个任务时，线程池中的线程数量不会超过核心线程的大小n

环境

jdk

1.8.x

maven

<!-- junit test -->
<dependency>
  <groupId>junit</groupId>
  <artifactId>junit</artifactId>
  <version>4.12</version>
  <scope>test</scope>
</dependency>

测试代码

/**
 * ThreadPoolExecutor测试类
 */
public class ThreadPoolExecutorTest {

    @Test
    public void testThreadCountNotGreaterThanCoreSize() throws InterruptedException {
        // 线程池中线程索引
        AtomicInteger pooledThreadIdx = new AtomicInteger(0);
        
        // 新建线程池
        ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(
                1,
                3,
                60L * 1000,
                TimeUnit.MILLISECONDS,
                // 任务队列为最大排队为10的任务队列
                new ArrayBlockingQueue<>(10),
                // 定制ThreadFactory，定义线程名称，以在多个线程池场景下区分业务线程
                r -> new Thread(r, "executor-tester" + pooledThreadIdx.getAndIncrement()),
                
                // 如果排队数量超过10，且线程最大已经达到maximumPoolSize时，再有任务提交时的拒绝策略
                // 一般是直接拒绝：表示服务仅能支撑这么多
                new ThreadPoolExecutor.AbortPolicy()
        );

        AtomicBoolean pass = new AtomicBoolean(false);

        // 向线程池提交11个任务
        submitTask(threadPoolExecutor, pass, 11);

        // 控制线程
        Thread controlThread = new Thread(() -> {
            int i = 0;
            while (i++ < 10) {
                // 先将自己睡眠一秒防止线程池还没有“反应过来”就获取活动线程数量为0的问题
                sleep(1000);
                
                // 睡眠一秒后再获取活动的线程数量应该为1,
                Assert.assertEquals(1, threadPoolExecutor.getActiveCount());
                StdOut.println("thread pool running workers: " + threadPoolExecutor.getActiveCount());
            }

            // 将线程中的任务全部放行
            pass.set(true);

            i = 0;
            // 等待大约2秒时间再判断线程池中的活动线程数量应该为0
            // 因为任务已经执行完成了
            while (i++ < 10) {
                sleep(200);
                StdOut.println("thread pool running workers: " + threadPoolExecutor.getActiveCount());
            }
            Assert.assertEquals(0, threadPoolExecutor.getActiveCount());
            StdOut.println("thread pool running workers: " + threadPoolExecutor.getActiveCount());
        });
        controlThread.start();
        controlThread.join();
    }

    private void submitTask(ThreadPoolExecutor threadPoolExecutor, AtomicBoolean pass, int taskCount) {
        for (int i = 0; i < taskCount; i++) {
            threadPoolExecutor.submit(() -> {
                while (!pass.get()) {
                    StdOut.println(Thread.currentThread().getName() + ": Thread running..." );
                    sleep(1000);
                }
            });
        }
    }

    public static void sleep(long millis) {
        try {
            Thread.sleep(millis);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

Console输出

executor-tester0: Thread running...
executor-tester0: Thread running...
thread pool running workers: 1
executor-tester0: Thread running...
thread pool running workers: 1
executor-tester0: Thread running...
thread pool running workers: 1
executor-tester0: Thread running...
thread pool running workers: 1
executor-tester0: Thread running...
thread pool running workers: 1
thread pool running workers: 1
executor-tester0: Thread running...
executor-tester0: Thread running...
thread pool running workers: 1
executor-tester0: Thread running...
thread pool running workers: 1
executor-tester0: Thread running...
thread pool running workers: 1
executor-tester0: Thread running...
thread pool running workers: 1
thread pool running workers: 1
thread pool running workers: 1
thread pool running workers: 1
thread pool running workers: 1
thread pool running workers: 0
thread pool running workers: 0
thread pool running workers: 0
thread pool running workers: 0
thread pool running workers: 0
thread pool running workers: 0
thread pool running workers: 0
Disconnected from the target VM, address: '127.0.0.1:52409', transport: 'socket'

Process finished with exit code 0