public class ThreadPoolExecutor extends AbstractExecutorService {
    .....
    public ThreadPoolExecutor(int corePoolSize,int maximumPoolSize,long keepAliveTime,TimeUnit unit,
            BlockingQueue<Runnable> workQueue);
 
    public ThreadPoolExecutor(int corePoolSize,int maximumPoolSize,long keepAliveTime,TimeUnit unit,
            BlockingQueue<Runnable> workQueue,ThreadFactory threadFactory);
 
    public ThreadPoolExecutor(int corePoolSize,int maximumPoolSize,long keepAliveTime,TimeUnit unit,
            BlockingQueue<Runnable> workQueue,RejectedExecutionHandler handler);
 
    public ThreadPoolExecutor(int corePoolSize,int maximumPoolSize,long keepAliveTime,TimeUnit unit,
        BlockingQueue<Runnable> workQueue,ThreadFactory threadFactory,RejectedExecutionHandler handler);
    ...
}

 //原子操作整型类，32位，其中前3位表示线程状态，后29位标识线程的数量
 private final AtomicInteger ctl = new AtomicInteger(ctlOf(RUNNING, 0));

 public void execute(Runnable command) {
        //1.判断执行的线程任务是否空，如果为空抛出空指针异常
        if (command == null)
            throw new NullPointerException();
        //2.获取线程状态以及线程数量
        int c = ctl.get();
        //3.判断当前线程池数量是否小于corePoolSize，小于则创建新线程
        if (workerCountOf(c) < corePoolSize) {
            if (addWorker(command, true))
                return;
            c = ctl.get();
        }
        //4.如果线程处于运行状态同时线程可以添加到缓冲队列中
        if (isRunning(c) && workQueue.offer(command)) {
        //5.再次检查线程状态（防止上次检查后的线程已销毁或者出现线程池关闭的情况）
            int recheck = ctl.get();
        //6.如果当前线程状态不是运行状态，那么从队列中删除此任务，同时执行拒绝策略
            if (! isRunning(recheck) && remove(command))
                reject(command);
        //7.否则当前线程池为空，则创建一个线程
            else if (workerCountOf(recheck) == 0)
                addWorker(null, false);
        }
        //8.如果队列满了，则新增线程，新增失败则执行拒绝策略
        else if (!addWorker(command, false))
            reject(command);
    }

private boolean addWorker(Runnable firstTask, boolean core) {
        //1.通过cas来增加线程池中的线程个数
        retry:
        for (;;) {
            int c = ctl.get();
            int rs = runStateOf(c);

            // Check if queue empty only if necessary.
            if (rs >= SHUTDOWN &&
                ! (rs == SHUTDOWN &&
                   firstTask == null &&
                   ! workQueue.isEmpty()))
                return false;

            for (;;) {
                int wc = workerCountOf(c);
                if (wc >= CAPACITY ||
                    wc >= (core ? corePoolSize : maximumPoolSize))
                    return false;
                if (compareAndIncrementWorkerCount(c))
                    break retry;
                c = ctl.get();  // Re-read ctl
                if (runStateOf(c) != rs)
                    continue retry;
                // else CAS failed due to workerCount change; retry inner loop
            }
        }
        //2.并发安全的将任务添加到workers里面，同时启动任务执行
        boolean workerStarted = false;
        boolean workerAdded = false;
        Worker w = null;
        try {
            //创建worker
            w = new Worker(firstTask);
            final Thread t = w.thread;
            if (t != null) {
                final ReentrantLock mainLock = this.mainLock;
                //加锁，防止其他线程调用
                mainLock.lock();
                try {
                    //重新检查线程状态
                    int rs = runStateOf(ctl.get());

                    if (rs < SHUTDOWN ||
                        (rs == SHUTDOWN && firstTask == null)) {
                        if (t.isAlive()) // precheck that t is startable
                            throw new IllegalThreadStateException();
                        //添加任务
                        workers.add(w);
                        int s = workers.size();
                        if (s > largestPoolSize)
                            largestPoolSize = s;
                        workerAdded = true;
                    }
                } finally {
                    mainLock.unlock();
                }
                //添加成功则启动任务
                if (workerAdded) {
                    t.start();
                    workerStarted = true;
                }
            }
        } finally {
            if (! workerStarted)
                addWorkerFailed(w);
        }
        return workerStarted;
    }