解析ThreadPoolExecutor类是如何保证线程池正确运行的。

//主要用来保存线程数量和线程池的状态，高3位保存线程状态，低29位保存线程数量
private final AtomicInteger ctl = new AtomicInteger(ctlOf(RUNNING, 0));
//线程池中线程的数量的位数（32-3）
private static final int COUNT_BITS = Integer.SIZE - 3;
//表示线程池中的最大线程数量
//将数字1的二进制值向右移29位，再减去1
private static final int CAPACITY   = (1 << COUNT_BITS) - 1;
//线程池的运行状态
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;
//获取线程状态
private static int runStateOf(int c)     { return c & ~CAPACITY; }
//获取线程数量
private static int workerCountOf(int c)  { return c & CAPACITY; }
private static int ctlOf(int rs, int wc) { return rs | wc; }
private static boolean runStateLessThan(int c, int s) {
	return c < s;
}
private static boolean runStateAtLeast(int c, int s) {
	return c >= s;
}
private static boolean isRunning(int c) {
	return c < SHUTDOWN;
}
private boolean compareAndIncrementWorkerCount(int expect) {
	return ctl.compareAndSet(expect, expect + 1);
}
private boolean compareAndDecrementWorkerCount(int expect) {
	return ctl.compareAndSet(expect, expect - 1);
}
private void decrementWorkerCount() {
	do {} while (! compareAndDecrementWorkerCount(ctl.get()));
}

//用于存放任务的阻塞队列  
private final BlockingQueue<Runnable> workQueue;
//可重入锁
private final ReentrantLock mainLock = new ReentrantLock();
//存放线程池中线程的集合，访问这个集合时，必须获得mainLock锁
private final HashSet<Worker> workers = new HashSet<Worker>();
//在锁内部阻塞等待条件完成
private final Condition termination = mainLock.newCondition();
//线程工厂，以此来创建新线程
private volatile ThreadFactory threadFactory;
//拒绝策略
private volatile RejectedExecutionHandler handler;
//默认的拒绝策略
private static final RejectedExecutionHandler defaultHandler = new AbortPolicy();

private final class Worker extends AbstractQueuedSynchronizer implements Runnable{
	private static final long serialVersionUID = 6138294804551838833L;
	//真正执行任务的线程
	final Thread thread;
	//第一个Runnable任务，如果在创建线程时指定了需要执行的第一个任务
	//则第一个任务会存放在此变量中，此变量也可以为null
	//如果为null，则线程启动后，通过getTask方法到BlockingQueue队列中获取任务
	Runnable firstTask;
	//用于存放此线程完全的任务数，注意：使用了volatile关键字
	volatile long completedTasks;
 
	//Worker类唯一的构造放大，传递的firstTask可以为null
	Worker(Runnable firstTask) {
		//防止在调用runWorker之前被中断
		setState(-1);
		this.firstTask = firstTask;
		//使用ThreadFactory 来创建一个新的执行任务的线程
		this.thread = getThreadFactory().newThread(this);
	}
	//调用外部ThreadPoolExecutor类的runWorker方法执行任务
	public void run() {
		runWorker(this);
	}

	//是否获取到锁 
	//state=0表示锁未被获取
	//state=1表示锁被获取
	protected boolean isHeldExclusively() {
		return getState() != 0;
	}

	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) {
			}
		}
	}
}