public interface ThreadFactory {  
    Thread newThread(Runnable r);  
}  

static class DefaultThreadFactory implements ThreadFactory {  
        private static final AtomicInteger poolNumber = new AtomicInteger(1);  
        private final ThreadGroup group;  
        private final AtomicInteger threadNumber = new AtomicInteger(1);  
        private final String namePrefix;  
  
        DefaultThreadFactory() {  
            SecurityManager s = System.getSecurityManager();  
            group = (s != null) ? s.getThreadGroup() :  
                                  Thread.currentThread().getThreadGroup();  
            namePrefix = "pool-" +  
                          poolNumber.getAndIncrement() +  
                         "-thread-";  
        }  
  
        public Thread newThread(Runnable r) {  
            Thread t = new Thread(group, r,  
                                  namePrefix + threadNumber.getAndIncrement(),  
                                  0);  
            if (t.isDaemon())  
                t.setDaemon(false);  
            if (t.getPriority() != Thread.NORM_PRIORITY)  
                t.setPriority(Thread.NORM_PRIORITY);  
            return t;  
        }  
    }  

public ThreadPoolExecutor(int corePoolSize,  
                          int maximumPoolSize,  
                          long keepAliveTime,  
                          TimeUnit unit,  
                          BlockingQueue<Runnable> workQueue) {  
    this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue,  
         Executors.defaultThreadFactory(), defaultHandler);  
}  
public ThreadPoolExecutor(int corePoolSize,  
                          int maximumPoolSize,  
                          long keepAliveTime,  
                          TimeUnit unit,  
                          BlockingQueue<Runnable> workQueue,  
                          RejectedExecutionHandler handler) {  
    this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue,  
         Executors.defaultThreadFactory(), handler);  
}  
public ThreadPoolExecutor(int corePoolSize,  
                          int maximumPoolSize,  
                          long keepAliveTime,  
                          TimeUnit unit,  
                          BlockingQueue<Runnable> workQueue,  
                          ThreadFactory threadFactory) {  
    this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue,  
         threadFactory, defaultHandler);  
}  
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.corePoolSize = corePoolSize;  
    this.maximumPoolSize = maximumPoolSize;  
    this.workQueue = workQueue;  
    this.keepAliveTime = unit.toNanos(keepAliveTime);  
    this.threadFactory = threadFactory;  
    this.handler = handler;  
}  

private boolean addWorker(Runnable firstTask, boolean core) {  
        retry:  
        for (;;) { // 外层循环，负责判断线程池状态  
            int c = ctl.get();  
            int rs = runStateOf(c);  
<span style="white-space:pre">  </span>    // 线程池状态值的大小为:RUNNING < SHUTDOWN < STOP < TIDYING < TERMINATED  
            // 有如下几种场景是可以直接拒绝增加新线程的：rs至少是SHUTDOWN状态，以下3个条件任意一个是false（1）rs==SHUTDOWN,false的情况是：线程池已经超过了SHUTDOWn状态，可能是STOP，TIDYING，TERMINATED其中之一，即线程已经终止了（2）firstTask==null,隐含rs==SHUTDOWN,false:firstTask!=null,场景是线程池已经shutdown，还要添加新的任务，拒绝（3）!workQueue.isEmpty(),隐含rs==SHUTDOWN && firstTask==null,false:wq为空，当firstTask为空是为了创建一个没有任务的线程，从wq中获取任务，如果wq为空，就没有添加新线程的必要了。  
            if (rs >= SHUTDOWN &&  
                ! (rs == SHUTDOWN &&  
                   firstTask == null &&  
                   ! workQueue.isEmpty()))  
                return false;  
  
            for (;;) { // 内层循环，负责workerCount + 1  
                int wc = workerCountOf(c);  
                if (wc >= CAPACITY ||  
                    wc >= (core ? corePoolSize : maximumPoolSize)) // 如果wc > 线程池最大上限CAPACITY，或者wc > corePoolSize(maximumPoolSize)  
                    return false;  
                if (compareAndIncrementWorkerCount(c)) // CAS操作，使得wc + 1，成功则跳出retry循环，标示累加成功  
                    break retry;  
                c = ctl.get();  // Re-read ctl  
                if (runStateOf(c) != rs) // 如果之前的CAS操作失败，需要从新获取线程池状态，如果与之前不一致，跳出内循环，继续去外层循环判断  
                    continue retry;  
                // else CAS failed due to workerCount change; retry inner loop  
            }  
        }  
  
        boolean workerStarted = false; // 线程是否启动成功  
        boolean workerAdded = false; // 线程是否增加成功  
        Worker w = null;  
        try {  
            w = new Worker(firstTask);  
            final Thread t = w.thread;  
            if (t != null) {  
                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());  
  
                    if (rs < SHUTDOWN ||  
                        (rs == SHUTDOWN && firstTask == null)) { // 如果线程池在运行，或者线程池已经shutdown且firstTask==null（可能是wq中有未执行完成的任务，攒国家没有初始化的worker去执行队列中的任务）  
                        if (t.isAlive()) // precheck that t is startable  
                            throw new IllegalThreadStateException();  
                        workers.add(w);  
                        int s = workers.size();  
                        if (s > largestPoolSize)  
                            largestPoolSize = s;  
                        workerAdded = true;  
                    }  
                } finally {  
                    mainLock.unlock();  
                }  
                if (workerAdded) { // 如果添加成功，则启动线程  
                    t.start();  
                    workerStarted = true;  
                }  
            }  
        } finally {  
            if (! workerStarted) // 如果启动失败  
                addWorkerFailed(w);  
        }  
        return workerStarted;  
    }