面试题：线程池内线程没有catch处理，抛出异常，线程池会怎么办？

答案

当线程池中线程执行任务的时候，任务出现未被捕获的异常的情况下，线程池会将允许该任务的线程从池中移除并销毁，且同时会创建一个新的线程加入到线程池中；可以通过ThreadFactory自定义线程并捕获线程内抛出的异常，也就是说甭管我们是否去捕获和处理线程池中工作线程抛出的异常，这个线程都会从线程池中被移除

源码

这道面试题源码在ThreadPoolExecutor#runWorker()方法中

任务运行是task.run()，进行了try catch处理，catch中将异常直接抛出，所以用户没有进行任何处理时，异常直接抛出。

(afterExecute方法是为了提供给扩展)

然后task置为null， 完成任务数加1，主要看后面的finally中调用的processWorkerExit方法

decrementWorkerCount()将CAS内存中worker存值减一，workers.remove(w)将工作线程移除

public class ThreadPoolExecutor extends AbstractExecutorService {
    final void runWorker(Worker w) {
        Thread wt = Thread.currentThread();
        Runnable task = w.firstTask;
        w.firstTask = null;
        w.unlock(); // allow interrupts
        boolean completedAbruptly = true;
        try {
            while (task != null || (task = getTask()) != null) {
                w.lock();
                // If pool is stopping, ensure thread is interrupted;
                // if not, ensure thread is not interrupted.  This
                // requires a recheck in second case to deal with
                // shutdownNow race while clearing interrupt
                if ((runStateAtLeast(ctl.get(), STOP) ||
                     (Thread.interrupted() &&
                      runStateAtLeast(ctl.get(), STOP))) &&
                    !wt.isInterrupted())
                    wt.interrupt();
                try {
                    beforeExecute(wt, task);
                    Throwable thrown = null;
                    try {
                        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 {
            // 移除线程池
            processWorkerExit(w, completedAbruptly);
        }
    }
}

protected void afterExecute(Runnable r, Throwable t) { }

public class ThreadPoolExecutor extends AbstractExecutorService {
    private void processWorkerExit(Worker w, boolean completedAbruptly) {
        if (completedAbruptly) // If abrupt, then workerCount wasn't adjusted
            // CAS内存中值减一
            decrementWorkerCount();

        final ReentrantLock mainLock = this.mainLock;
        mainLock.lock();
        try {
            completedTaskCount += w.completedTasks;
            // 移除线程池
            workers.remove(w);
        } finally {
            mainLock.unlock();
        }

        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
            }
            addWorker(null, false);
        }
    }
}

https://blog.csdn.net/luxiaoruo/article/details/106637384