ThreadPoolExecutor源码解析（一）

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

        //创建一个可缓存线程池，如果线程池长度超过处理需要，可灵活回收空闲线程，若无可回收，则新建线程。
　　　　 //通过设置corePoolSize为0，而maximumPoolSize为Integer.Max_VALUE（Int型数据最大值）实现。
　　　　 ExecutorService cache = Executors.newCachedThreadPool();
　　　　 //创建一个定长线程池，可控制线程最大并发数，超出的线程会在队列中等待。
　　　　 //通过将corePoolSize和maximumPoolSize的值设置为一样的值来实现。
        ExecutorService fixed = Executors.newFixedThreadPool(num);
　　　　 //创建一个定长线程池，支持定时及周期性任务执行。
　　　　 //通过将队列参数workQueue设置为DelayWorkQueue来实现。
        ExecutorService schedule = Executors.newScheduledThreadPool(5);
　　　　 //创建一个单线程化的线程池，它只会用唯一的工作线程来执行任务，保证所有任务按照指定顺序(FIFO, LIFO, 优先级)执行。
　　　　 //通过将corePoolSize和maximumPoolSize都设置为1来实现。
        ExecutorService single = Executors.newSingleThreadExecutor();

    /**
     * Woker主要维护着运行task的worker的中断控制信息，以及其他小记录。这个类拓展AbstractQueuedSynchronizer
     * 而来简化获取和释放每一个任务执行中的锁。这可以防止中断那些打算唤醒正在等待其他线程任务的任务，而不是
     * 中断正在运行的任务。我们实现一个简单的不可重入锁而不是ReentrantLo，因为我们不想当其调用setCorePoolSize
     * 这样的方法的时候能获得锁。
     */
    //worker主要是对进行中的任务进行中断控制，顺带着对其他行为进行记录
    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;

        /** Thread this worker is running in.  Null if factory fails. */
        //正在跑的线程，如果是null标识factory失败
        final Thread thread;
        /** Initial task to run.  Possibly null. */
        //初始化一个任务以运行
        Runnable firstTask;
        /** Per-thread task counter */
        //每个线程计数
        volatile long completedTasks;

        /**
         * Creates with given first task and thread from ThreadFactory.
         * @param firstTask the first task (null if none)
         * 用给定的first task和从threadFactory创建
         */
        Worker(Runnable firstTask) {
            setState(-1); // inhibit interrupts until runWorker
            this.firstTask = firstTask;
            this.thread = getThreadFactory().newThread(this);
        }


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

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

        //
        protected boolean isHeldExclusively() {
            return getState() != 0;
        }

        //尝试获取锁
        protected boolean tryAcquire(int unused) {
            if (compareAndSetState(0, 1)) {
                setExclusiveOwnerThread(Thread.currentThread());
                return true;
            }
            return false;
        }
        //尝试释放锁
        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) {
                }
            }
        }
    }

    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;

    // Packing and unpacking ctl  
　　//拆包ctl，分别获取runState和WorkerCount
    private static int runStateOf(int c)     { return c & ~CAPACITY; }
    private static int workerCountOf(int c)  { return c & CAPACITY; }
　　//打包操作
    private static int ctlOf(int rs, int wc) { return rs | wc; }