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//高3位：表示当前线程池运行状态   除去高3位之后的低位：表示当前线程池中所拥有的线程数量
    private final AtomicInteger ctl = new AtomicInteger(ctlOf(RUNNING, 0));
    //表示在ctl中，低COUNT_BITS位 是用于存放当前线程数量的位。
    private static final int COUNT_BITS = Integer.SIZE - 3;
    //低COUNT_BITS位 所能表达的最大数值。 000 11111111111111111111 => 5亿多。
    private static final int CAPACITY   = (1 << COUNT_BITS) - 1;

    // runState is stored in the high-order bits
    //111 000000000000000000  转换成整数，其实是一个负数
    private static final int RUNNING    = -1 << COUNT_BITS;
    //000 000000000000000000
    private static final int SHUTDOWN   =  0 << COUNT_BITS;
    //001 000000000000000000
    private static final int STOP       =  1 << COUNT_BITS;
    //010 000000000000000000
    private static final int TIDYING    =  2 << COUNT_BITS;
    //011 000000000000000000
    private static final int TERMINATED =  3 << COUNT_BITS;

    // Packing and unpacking ctl
    //获取当前线程池运行状态
    //~000 11111111111111111111 => 111 000000000000000000000
    //c == ctl = 111 000000000000000000111
    //111 000000000000000000111
    //111 000000000000000000000
    //111 000000000000000000000
    private static int runStateOf(int c)     { return c & ~CAPACITY; }

    //获取当前线程池线程数量
    //c == ctl = 111 000000000000000000111
    //111 000000000000000000111
    //000 111111111111111111111
    //000 000000000000000000111 => 7
    private static int workerCountOf(int c)  { return c & CAPACITY; }

    //用在重置当前线程池ctl值时  会用到
    //rs 表示线程池状态   wc 表示当前线程池中worker（线程）数量
    //111 000000000000000000
    //000 000000000000000111
    //111 000000000000000111
    private static int ctlOf(int rs, int wc) { return rs | wc; }

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select * from t force index(a) where a between 10000 and 20000;
// 利用参数force index