肝完这篇线程池，我咳血了（四）

Worker(Runnable firstTask) {
  setState(-1); 
  this.firstTask = firstTask;
  this.thread = getThreadFactory().newThread(this);
}

final void runWorker(Worker w) {
  Thread wt = Thread.currentThread();
  Runnable task = w.firstTask;
  w.firstTask = null;
  // 允许打断
  //  new Worker() 是 state==-1，此处是调用 Worker 类的 tryRelease() 方法，
  //  将 state 置为0
  w.unlock();
  boolean completedAbruptly = true;
  try {
    // 调用 getTask() 获取任务
    while (task != null || (task = getTask()) != null) {
      // 获取全局锁
      w.lock();
      // 确保只有在线程 STOPING 时，才会被设置中断标志，否则清除中断标志。
      // 如果一开始判断线程池状态 < STOPING，但 Thread.interrupted() 为 true，
      // 即线程已经被中断，又清除了中断标示，再次判断线程池状态是否 >= stop
      // 是，再次设置中断标示，wt.interrupt()
      // 否，不做操作，清除中断标示后进行后续步骤
      if ((runStateAtLeast(ctl.get(), STOP) ||
           (Thread.interrupted() &&
            runStateAtLeast(ctl.get(), STOP))) &&
          !wt.isInterrupted())
        wt.interrupt();
      try {
        // 执行前需要调用的方法，交给程序员自己来实现
        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 {
          // 执行后需要调用的方法，交给程序员自己来实现
          afterExecute(task, thrown);
        }
      } finally {
        // 把 task 置为 null，完成任务数 + 1，并进行解锁
        task = null;
        w.completedTasks++;
        w.unlock();
      }
    }
    completedAbruptly = false;
    // 最后处理 worker 的退出
  } finally {
    processWorkerExit(w, completedAbruptly);
  }
}

private Runnable getTask() {
  // 判断最后一个 poll 是否超时。
  boolean timedOut = false; // Did the last poll() time out?
  for (;;) {
    int c = ctl.get();
    int rs = runStateOf(c);
    // Check if queue empty only if necessary.
    // 必要时检查队列是否为空
    // 对线程池状态的判断，两种情况会 workerCount-1，并且返回 null
    // 线程池状态为 shutdown，且 workQueue 为空（反映了 shutdown 状态的线程池还是要执行 workQueue 中剩余的任务的）
    // 线程池状态为 stop（shutdownNow() 会导致变成 STOP）（此时不用考虑 workQueue 的情况）
    if (rs >= SHUTDOWN && (rs >= STOP || workQueue.isEmpty())) {
      decrementWorkerCount();
      return null;
    }
    int wc = workerCountOf(c);
    // Are workers subject to culling?
    // 是否需要定时从 workQueue 中获取
    boolean timed = allowCoreThreadTimeOut || wc > corePoolSize;
    // 如果工作线程的数量大于 maximumPoolSize 会进行线程剔除
    // 如果使用了 allowCoreThreadTimeOut ，并且工作线程不为0或者队列有任务的话，会直接进行线程剔除
    if ((wc > maximumPoolSize || (timed && timedOut))
        && (wc > 1 || workQueue.isEmpty())) {
      if (compareAndDecrementWorkerCount(c))
        return null;
      continue;
    }
    try {
      Runnable r = timed ?
        workQueue.poll(keepAliveTime, TimeUnit.NANOSECONDS) :
      workQueue.take();
      if (r != null)
        return r;
      timedOut = true;
    } catch (InterruptedException retry) {
      timedOut = false;
    }
  }
}

private void processWorkerExit(Worker w, boolean completedAbruptly) {
  // worker数量 -1
  // completedAbruptly 是 true，突然终止，说明是 task 执行时异常情况导致，即run()方法执行时发生了异常，那么正在工作的 worker 线程数量需要-1
  // completedAbruptly 是 false 是突然终止，说明是 worker 线程没有 task 可执行了，不用-1，因为已经在 getTask() 方法中-1了
  if (completedAbruptly) // If abrupt, then workerCount wasn't adjusted
    decrementWorkerCount();
  // 从 Workers Set 中移除 worker
  final ReentrantLock mainLock = this.mainLock;
  mainLock.lock();
  try {
    completedTaskCount += w.completedTasks;
    workers.remove(w);
  } finally {
    mainLock.unlock();
  }
  // 尝试终止线程，
  tryTerminate();
  // 是否需要增加 worker 线程
  // 线程池状态是 running 或 shutdown
  // 如果当前线程是突然终止的，addWorker()
  // 如果当前线程不是突然终止的，但当前线程数量 < 要维护的线程数量，addWorker()
  // 故如果调用线程池 shutdown()，直到workQueue为空前，线程池都会维持 corePoolSize 个线程，
  // 然后再逐渐销毁这 corePoolSize 个线程
  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);
  }
}

public static ExecutorService newFixedThreadPool(int nThreads) {
  return new ThreadPoolExecutor(nThreads, nThreads,
                                0L, TimeUnit.MILLISECONDS,
                                new LinkedBlockingQueue<Runnable>());
}

public static ExecutorService newSingleThreadExecutor(ThreadFactory threadFactory) {
  return new FinalizableDelegatedExecutorService
    (new ThreadPoolExecutor(1, 1,
                            0L, TimeUnit.MILLISECONDS,
                            new LinkedBlockingQueue<Runnable>(),
                            threadFactory));
}

public static ExecutorService newCachedThreadPool(ThreadFactory threadFactory) {
  return new ThreadPoolExecutor(0, Integer.MAX_VALUE,
                                60L, TimeUnit.SECONDS,
                                new SynchronousQueue<Runnable>(),
                                threadFactory);
}