addWorker

private boolean addWorker(Runnable firstTask, boolean core) {
        retry:
        for (;;) {
            int c = ctl.get();
			//获取当前状态
            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);
				//如果线程数量大于最大值 
			   //或者 如果创建核心线程的情况下，线程数大于核心线程
			   //或者 创建非核心线程的情况下 线程数大于了最大线程数
			   //直接返回false
                if (wc >= CAPACITY ||
                    wc >= (core ? corePoolSize : maximumPoolSize))
                    return false;
					//调用了原子类的CAS，如果成功 退出循环 原子类 会在后面章节介绍
                if (compareAndIncrementWorkerCount(c))
                    break retry;
				//如果失败了 重新获取一下c的值
                c = ctl.get();  // Re-read ctl
				// 状态发生了变化 从头开始 ，否则就是走for(;;)逻辑
                if (runStateOf(c) != rs)
                    continue retry;
                // else CAS failed due to workerCount change; retry inner loop
            }
        }

        //走到这里 才是真正的创建逻辑
		//走到这里 肯定会创建一个线程
		//如果线程满了 走不到这 
		//所以workers的数量就是线程的数量
        boolean workerStarted = false;
        boolean workerAdded = false;
        Worker w = null;
        try {
		  //new了一个Worker ，Worker是个啥呢 看下面 
		  //简单来说 就是包装了一个线程和Runnable任务的 任务类，负责真正干活的类
            w = new Worker(firstTask);
            final Thread t = w.thread;
            if (t != null) {
			  //这里有一个Java重入锁 也会在后面介绍 现在知道他就是个锁就行了 起到并发安全的作用
                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)) {
                        if (t.isAlive()) // precheck that t is startable
                            throw new IllegalThreadStateException();
						//添加到队列里
                        workers.add(w);
                        int s = workers.size();
                        if (s > largestPoolSize)
                            largestPoolSize = s;
                        workerAdded = true;
                    }
                } finally {
                    mainLock.unlock();
                }
                if (workerAdded) {
				   //添加了线程 就启动一下
				   //因为Worker是个runnable 所以start线程就自动执行run方法了
				   //run方法逻辑 看下面
                    t.start();
                    workerStarted = true;
                }
            }
        } finally {
            if (! workerStarted)
                addWorkerFailed(w);
        }
        return workerStarted;
    }

Worker 是个啥

是一个Runnable
又继承了AQS（这个会再重入锁那一章节讲）

 private final class Worker
        extends AbstractQueuedSynchronizer
        implements Runnable
    {
	
	  /** Thread this worker is running in.  Null if factory fails. */
        final Thread thread;
        /** Initial task to run.  Possibly null. */
        Runnable firstTask;
        /** Per-thread task counter */
        volatile long completedTasks;
		
 Worker(Runnable firstTask) {
            setState(-1); // inhibit interrupts until runWorker
            this.firstTask = firstTask;
            this.thread = getThreadFactory().newThread(this);
        }
}

run

既然是个runnable run方法就很重要了

public void run() {
            runWorker(this);
        }
		final void runWorker(Worker w) {
        Thread wt = Thread.currentThread();
		//先获取当初创建worker时传入的那个任务
        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
				//如果STOP了 执行interrupt逻辑
                if ((runStateAtLeast(ctl.get(), STOP) ||
                     (Thread.interrupted() &&
                      runStateAtLeast(ctl.get(), STOP))) &&
                    !wt.isInterrupted())
                    wt.interrupt();
                try {
                    beforeExecute(wt, task);
                    Throwable thrown = null;
                    try {
					  //执行
                        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 {
		//上面返回任务为null会走到这里 下一章介绍这个方法
            processWorkerExit(w, completedAbruptly);
        }
    }
	//找到一个可以执行的任务 主要是这个逻辑
	private Runnable getTask() {
        boolean timedOut = false; // Did the last poll() time out?

        for (;;) {
            int c = ctl.get();
            int rs = runStateOf(c);
			//如果SHUTDOWN了 任务数量-1 返回 如果一直是这种状态 就一直减 减到0
            // Check if queue empty only if necessary.
            if (rs >= SHUTDOWN && (rs >= STOP || workQueue.isEmpty())) {
                decrementWorkerCount();
                return null;
            }
			//
            int wc = workerCountOf(c);

            // Are workers subject to culling?
			//allowCoreThreadTimeOut 默认是false
			//也就是只有核心线程的情况会 timed是false 取任务
			//存在非核心情况下，会在限定keepAliveTime的时间内获取任务,如果没有就返回空
			//返回空之后就会走processWorkerExit 这个逻辑
            boolean timed = allowCoreThreadTimeOut || wc > corePoolSize;

            if ((wc > maximumPoolSize || (timed && timedOut))
                && (wc > 1 || workQueue.isEmpty())) {
                if (compareAndDecrementWorkerCount(c))
                    return null;
                continue;
            }

         //从队列里获取一个任务
            try {
                Runnable r = timed ?
				//队列也会在后面章节介绍
                    workQueue.poll(keepAliveTime, TimeUnit.NANOSECONDS) :
					//移除并返回队列头部的元素     如果队列为空，则阻塞
                    workQueue.take();
                if (r != null)
                    return r;
                timedOut = true;
            } catch (InterruptedException retry) {
                timedOut = false;
            }
        }
    }

compareAndIncrementWorkerCount

    /**
     * Attempts to CAS-increment the workerCount field of ctl.
     */
    private boolean compareAndIncrementWorkerCount(int expect) {
        return ctl.compareAndSet(expect, expect + 1);
    }