public ThreadPoolExecutor(int corePoolSize,
                              int maximumPoolSize,
                              long keepAliveTime,
                              TimeUnit unit,
                              BlockingQueue<Runnable> workQueue,
                              ThreadFactory threadFactory,
                              RejectedExecutionHandler handler) {
        if (corePoolSize < 0 ||
            maximumPoolSize <= 0 ||
            maximumPoolSize < corePoolSize ||
            keepAliveTime < 0)
            throw new IllegalArgumentException();
        if (workQueue == null || threadFactory == null || handler == null)
            throw new NullPointerException();
        this.acc = System.getSecurityManager() == null ?
                null :
                AccessController.getContext();
        this.corePoolSize = corePoolSize;
        this.maximumPoolSize = maximumPoolSize;
        this.workQueue = workQueue;
        this.keepAliveTime = unit.toNanos(keepAliveTime);
        this.threadFactory = threadFactory;
        this.handler = handler;
    }

private final AtomicInteger ctl = new AtomicInteger(ctlOf(RUNNING, 0));
private static final int COUNT_BITS = Integer.SIZE - 3;
private static final int CAPACITY   = (1 << COUNT_BITS) - 1;

// runState is stored in the high-order bits
private static final int RUNNING    = -1 << COUNT_BITS;
private static final int SHUTDOWN   =  0 << COUNT_BITS;
private static final int STOP       =  1 << COUNT_BITS;
private static final int TIDYING    =  2 << COUNT_BITS;
private static final int TERMINATED =  3 << COUNT_BITS;

//获取运行状态
private static int runStateOf(int c)     { return c & ~CAPACITY; }
//获取活动线程数
private static int workerCountOf(int c)  { return c & CAPACITY; }
//获取运行状态和活动线程数
private static int ctlOf(int rs, int wc) { return rs | wc; }

public void execute(Runnable command) {
        if (command == null)
            throw new NullPointerException();
        int c = ctl.get();
    	//workerCount < corePoolSize
        if (workerCountOf(c) < corePoolSize) {
            //创建一个新的线程放入线程池，并将任务加到该线程。
            if (addWorker(command, true))
                return;
            //如果添加失败，更新c
            c = ctl.get();
        }
    	//判断当前线程池是RUNNING状态，并且将任务添加到workQueue成功
        if (isRunning(c) && workQueue.offer(command)) {
            //重新获取ctl的值
            int recheck = ctl.get();
            //再次判断线程池的状态，如果不是运行状态，将任务移出队列成功后，进行拒绝
            if (! isRunning(recheck) && remove(command))
                reject(command);
            //如果workCount == 0，则添加新线程
            else if (workerCountOf(recheck) == 0)
                addWorker(null, false);
        }
    	//1. 线程不是RUNNING状态 2.线程池是RUNNING状态，但是workerCount >= corePoolSize && workerCount已满
        else if (!addWorker(command, false))
            //失败则进行拒绝
            reject(command);
    }

private boolean addWorker(Runnable firstTask, boolean core) {
        retry:
        for (;;) {
            //获取线程池运行状态
            int c = ctl.get();
            int rs = runStateOf(c);

            //如果rs >= SHUTDOWN，则表示此时不再接收新任务
            //再检查三个条件，其中一个不满足则添加失败
            //1. rs == SHUTDOWN：关闭状态则不接受新任务
            //2. firstTask为空
            //3. 阻塞队列不为空
            //队列中没有任务则不需要再添加线程
            if (rs >= SHUTDOWN &&
                ! (rs == SHUTDOWN &&
                   firstTask == null &&
                   ! workQueue.isEmpty()))
                return false;

            for (;;) {
                //获取线程数量
                int wc = workerCountOf(c);
                //检查线程数量是否超过CAPACITY（二进制为29个1）
                //根据传入的core判断与哪个参数进行对比
                if (wc >= CAPACITY ||
                    wc >= (core ? corePoolSize : maximumPoolSize))
                    //如果条件成立，则拒绝创建线程
                    return false;
                //CAS尝试增加workerCount，成功则跳出外层循环
                if (compareAndIncrementWorkerCount(c))
                    break retry;
                c = ctl.get();  // Re-read ctl
                //当前运行状态不等于rs，说明状态已改变，则返回内层循环继续执行
                if (runStateOf(c) != rs)
                    continue retry;
                // else CAS failed due to workerCount change; retry inner loop
            }
        }

        boolean workerStarted = false;
        boolean workerAdded = false;
        Worker w = null;
        try {
            //根据firstTask创建Worker对象
            w = new Worker(firstTask);
            //获取worker的thread
            final Thread t = w.thread;
            if (t != null) {
                //上一个可重入锁
                final ReentrantLock mainLock = this.mainLock;
                mainLock.lock();
                try {
                    // Recheck while holding lock.
                    // Back out on ThreadFactory failure or if
                    // shut down before lock acquired.
                    int rs = runStateOf(ctl.get());
					//rs < SHUTDOWN表示是RUNNING状态
                    //或者是RUNING状态并且firstTask为null
                    if (rs < SHUTDOWN ||
                        (rs == SHUTDOWN && firstTask == null)) {
                        if (t.isAlive()) // precheck that t is startable
                            throw new IllegalThreadStateException();
                        //将worker加入工作线程集合中。
                        workers.add(w);
                        int s = workers.size();
                        // largestPoolSize记录着线程池中出现过的最大线程数量
                        //如果添加之后的工作线程集合size > largestPoolSize
                        if (s > largestPoolSize)
                            //更新线程池中出现的最大线程数量
                            largestPoolSize = s;
                        workerAdded = true;
                    }
                } finally {
                    mainLock.unlock();
                }
                if (workerAdded) {
                    //添加成功，启动线程执行任务
                    t.start();
                    workerStarted = true;
                }
            }
        } finally {
            if (! workerStarted)
                addWorkerFailed(w);
        }
        return workerStarted;
    }

public static class CallerRunsPolicy implements RejectedExecutionHandler {
        
        public CallerRunsPolicy() { }

        public void rejectedExecution(Runnable r, ThreadPoolExecutor e) {
            if (!e.isShutdown()) {
                r.run();
            }
        }
    }

    public static class AbortPolicy implements RejectedExecutionHandler {

        public AbortPolicy() { }

        public void rejectedExecution(Runnable r, ThreadPoolExecutor e) {
            throw new RejectedExecutionException("Task " + r.toString() +
                                                 " rejected from " +
                                                 e.toString());
        }
    }

    public static class DiscardPolicy implements RejectedExecutionHandler {

        public DiscardPolicy() { }

        public void rejectedExecution(Runnable r, ThreadPoolExecutor e) {
        }
    }

    public static class DiscardOldestPolicy implements RejectedExecutionHandler {

        public DiscardOldestPolicy() { }

        public void rejectedExecution(Runnable r, ThreadPoolExecutor e) {
            if (!e.isShutdown()) {
                e.getQueue().poll();
                e.execute(r);
            }
        }
    }

private final HashSet<Worker> workers = new HashSet<Worker>();

private final class Worker
        extends AbstractQueuedSynchronizer
        implements Runnable
    {
        /**
         * This class will never be serialized, but we provide a
         * serialVersionUID to suppress a javac warning.
         */
        private static final long serialVersionUID = 6138294804551838833L;

       //worker持有的线程
        final Thread thread;
       //初始化的任务，可以为null
        Runnable firstTask;
        //任务计数器
        volatile long completedTasks;

        /**
         * Creates with given first task and thread from ThreadFactory.
         * @param firstTask the first task (null if none)
         */
        Worker(Runnable firstTask) {
            //AQS默认为0，设置为-1是为了禁止执行任务前对线程进行中断
            setState(-1); // inhibit interrupts until runWorker
            this.firstTask = firstTask;
            //通过ThreadFactory创建线程
            this.thread = getThreadFactory().newThread(this);
        }

        /** Delegates main run loop to outer runWorker  */
        public void run() {
            runWorker(this);
        }

        // Lock methods
        //
        // The value 0 represents the unlocked state.
        // The value 1 represents the locked state.

        protected boolean isHeldExclusively() {
            return getState() != 0;
        }
		//不可重入
        protected boolean tryAcquire(int unused) {
            if (compareAndSetState(0, 1)) {
                setExclusiveOwnerThread(Thread.currentThread());
                return true;
            }
            return false;
        }

        protected boolean tryRelease(int unused) {
            setExclusiveOwnerThread(null);
            setState(0);
            return true;
        }

        public void lock()        { acquire(1); }
        public boolean tryLock()  { return tryAcquire(1); }
        public void unlock()      { release(1); }
        public boolean isLocked() { return isHeldExclusively(); }

        void interruptIfStarted() {
            Thread t;
            if (getState() >= 0 && (t = thread) != null && !t.isInterrupted()) {
                try {
                    t.interrupt();
                } catch (SecurityException ignore) {
                }
            }
        }
    }

final void runWorker(Worker w) {
    	//获取线程
        Thread wt = Thread.currentThread();
    	//获取第一个任务
        Runnable task = w.firstTask;
        w.firstTask = null;
    	//允许中断
        w.unlock();
    	//是否因为异常退出循环
        boolean completedAbruptly = true;
        try {
            //task为空，则通过getTask来获取任务
            while (task != null || (task = getTask()) != null) {
                //禁止中断
                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
                //如果线程池正在停止，保证当前线程是中断状态
                //如果不是，确保当前线程不是中断状态
                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 {
            processWorkerExit(w, completedAbruptly);
        }
    }

private Runnable getTask() {
        boolean timedOut = false; // Did the last poll() time out?
		//死循环获取队列任务
        for (;;) {
            int c = ctl.get();
            int rs = runStateOf(c);
			//判断线程池状态
            // Check if queue empty only if necessary.
            if (rs >= SHUTDOWN && (rs >= STOP || workQueue.isEmpty())) {
                //若已经停止，控制工作线程数量，并return null
                decrementWorkerCount();
                return null;
            }

            int wc = workerCountOf(c);

            // Are workers subject to culling?
            boolean timed = allowCoreThreadTimeOut || wc > corePoolSize;
			//控制线程数量
            if ((wc > maximumPoolSize || (timed && timedOut))
                && (wc > 1 || workQueue.isEmpty())) {
                if (compareAndDecrementWorkerCount(c))
                    return null;
                continue;
            }

            try {
                //取出任务
                Runnable r = timed ?
                    workQueue.poll(keepAliveTime, TimeUnit.NANOSECONDS) :
                    workQueue.take();
                if (r != null)
                    return r;
                timedOut = true;
            } catch (InterruptedException retry) {
                timedOut = false;
            }
        }
    }