详解Java线程池如何统计线程空闲时间

// 线程执行入口
public void run() {
    runWorker(this);
}

// 线程运行核心方法
final void runWorker(Worker w) {
    Thread wt = Thread.currentThread();
    Runnable task = w.firstTask;
    w.firstTask = null;
    w.unlock();
    boolean completedAbruptly = true;
    try {
        // 1. 使用while死循环，不断从阻塞队列中拉取任务
        while (task != null || (task = getTask()) != null) {
            // 加锁，保证thread不被其他线程中断（除非线程池被中断）
            w.lock();
            // 2. 校验线程池状态，是否需要中断当前线程
            if ((runStateAtLeast(ctl.get(), STOP) ||
                    (Thread.interrupted() &&
                            runStateAtLeast(ctl.get(), STOP))) &&
                    !wt.isInterrupted())
                wt.interrupt();
            try {
                beforeExecute(wt, task);
                Throwable thrown = null;
                try {
                    // 3. 执行run方法
                    task.run();
                } catch (RuntimeException x) {
                    thrown = x;
                    throw x;
                } catch (Error x) {
                    thrown = x;
                    throw x;
                } catch (Throwable x) {
                    thrown = x;
                    throw new Error(x);
                } finally {
                    afterExecute(task, thrown);
                }
            } finally {
                task = null;
                w.completedTasks++;
                w.unlock();
            }
        }
        completedAbruptly = false;
    } finally {
        processWorkerExit(w, completedAbruptly);
    }
}

// 从阻塞队列中拉取任务
private Runnable getTask() {
    boolean timedOut = false;
    for (; ; ) {
        int c = ctl.get();
        int rs = runStateOf(c);
        // 1. 如果线程池已经停了，或者阻塞队列是空，就回收当前线程
        if (rs >= SHUTDOWN && (rs >= STOP || workQueue.isEmpty())) {
            decrementWorkerCount();
            return null;
        }
        int wc = workerCountOf(c);
        // 2. 再次判断是否需要回收线程
        boolean timed = allowCoreThreadTimeOut || wc > corePoolSize;
        if ((wc > maximumPoolSize || (timed && timedOut))
                && (wc > 1 || workQueue.isEmpty())) {
            if (compareAndDecrementWorkerCount(c))
                return null;
            continue;
        }
        try {
            // 3. 在指定时间内，从阻塞队列中拉取任务
            Runnable r = timed ?
                    workQueue.poll(keepAliveTime, TimeUnit.NANOSECONDS) :
                    workQueue.take();
            if (r != null)
                return r;
          	// 4. 如果没有拉取到任务，就标识该线程已超时，然后就被回收
            timedOut = true;
        } catch (InterruptedException retry) {
            timedOut = false;
        }
    }
}

/**
 * @author 一灯架构
 * @apiNote 线程池示例
 **/
public class ThreadPoolDemo {
    public static void main(String[] args) {
        List<Integer> list = new ArrayList<>();
        // 1. 创建一个单个线程的线程池
        ExecutorService executorService = Executors.newSingleThreadExecutor();

        // 2. 往线程池中提交3个任务
        for (int i = 0; i < 3; i++) {
            executorService.execute(() -> {
                System.out.println(Thread.currentThread().getName() + " 关注公众号：一灯架构");
                throw new RuntimeException("抛异常了！");
            });
        }

        // 3. 关闭线程池
        executorService.shutdown();
    }

}

// 线程抛异常后，退出逻辑
private void processWorkerExit(ThreadPoolExecutor.Worker w, boolean completedAbruptly) {
    if (completedAbruptly)
        decrementWorkerCount();

    final ReentrantLock mainLock = this.mainLock;
    mainLock.lock();
    try {
        completedTaskCount += w.completedTasks;
        // 1. 从工作线程中删除当前线程
        workers.remove(w);
    } finally {
        mainLock.unlock();
    }

    // 2. 中断当前线程
    tryTerminate();

    int c = ctl.get();
    if (runStateLessThan(c, STOP)) {
        if (!completedAbruptly) {
            int min = allowCoreThreadTimeOut ? 0 : corePoolSize;
            if (min == 0 && !workQueue.isEmpty())
                min = 1;
            if (workerCountOf(c) >= min)
                return; // replacement not needed
        }
        // 3. 新建一个线程
        addWorker(null, false);
    }
}

/**
 * @author 一灯架构
 * @apiNote 线程池示例
 **/
public class ThreadPoolDemo {
    public static void main(String[] args) {
        List<Integer> list = new ArrayList<>();
        // 1. 创建一个单个线程的线程池
        ExecutorService executorService = Executors.newSingleThreadExecutor(runnable -> {
            // 2. 自定义线程创建工厂，并设置异常处理逻辑
            Thread thread = new Thread(runnable);
            thread.setUncaughtExceptionHandler((t, e) -> {
                System.out.println("捕获到异常：" + e.getMessage());
            });
            return thread;
        });

        // 3. 往线程池中提交3个任务
        for (int i = 0; i < 3; i++) {
            executorService.execute(() -> {
                System.out.println(Thread.currentThread().getName() + " 关注公众号：一灯架构");
                throw new RuntimeException("抛异常了！");
            });
        }

        // 4. 关闭线程池
        executorService.shutdown();
    }

}