// ctl 是一個整形原子類 , 它即表示了狀態(tài) , 有記錄了梳理
private final AtomicInteger ctl = new AtomicInteger(ctlOf(RUNNING, 0));
 //   : 此變量 記錄了 “線程池中的任務(wù)數(shù)量”和“線程池的狀態(tài)”兩個信息
//    : 高3位表示"線程池狀態(tài)"，低29位表示"線程池中的任務(wù)數(shù)量"
 //       - RUNNING : 111 : 該線程池能接收新任務(wù) ,且能對新任務(wù)進(jìn)行處理
 //       - SHUTDOWN : 000 : 不能接收新任務(wù) ,但是可以對任務(wù)進(jìn)行處理
//        - STOP : 001 : 不添加新任務(wù) , 不對任務(wù)進(jìn)行處理 , 會中斷正在執(zhí)行的任務(wù)
 //       - TIDYING : 010 : 當(dāng)所有的任務(wù)已終止，ctl記錄的"任務(wù)數(shù)量"為0，線程池會變?yōu)門IDYING狀態(tài)
 //           - 當(dāng)所有的任務(wù)已終止，ctl記錄的"任務(wù)數(shù)量"為0，線程池會變?yōu)門IDYING狀態(tài)
//        - TERMINATED : 011 : 線程池徹底終止的狀態(tài)
        
        
// 對數(shù)量的統(tǒng)計(jì)很簡單 , 因?yàn)槭?低 29 位用來描述梳理 , 所以做正常的加減即可實(shí)現(xiàn)
private boolean compareAndIncrementWorkerCount(int expect) {
    return ctl.compareAndSet(expect, expect + 1);
}

private boolean compareAndDecrementWorkerCount(int expect) {
    return ctl.compareAndSet(expect, expect - 1);
}


// 對狀態(tài)的修改則是通過位運(yùn)算來做的
> S1 : 預(yù)先準(zhǔn)備多種狀態(tài)
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;

> S2 : 判斷是否是運(yùn)行狀態(tài)或停止?fàn)顟B(tài)
private static final int COUNT_BITS = Integer.SIZE - 3;
private static final int CAPACITY   = (1 << COUNT_BITS) - 1;
// ~CAPACITY將反轉(zhuǎn)CAPACITY的值，也就是CAPACITY的高3位全部為1，低29位全部為0
// & 操作則可以得到高三位的值
private static int runStateOf(int c) { return c & ~CAPACITY; }
final boolean isRunningOrShutdown(boolean shutdownOK) {
    int rs = runStateOf(ctl.get());
    return rs == RUNNING || (rs == SHUTDOWN && shutdownOK);
}

3 << 60 | timestamp - 1504000000000L << 20 | workerId << 10 | random.nextInt(128);

// S1 : 初始化
private static final int NULL_HANDLE = -1;
private int passHandle = NULL_HANDLE;

// S2 : 寫入 passHandler (PS : 此處是在 ObjectOutputStream 中)
 bout.writeInt(baseWireHandle + passHandle);


// S3 : 解析 passHandler
passHandle = bin.readInt() - baseWireHandle;
if (passHandle < 0 || passHandle >= handles.size()) {
    throw new StreamCorruptedException...
}


// S4 : 通過 Handler 取位數(shù)
Object lookupObject(int handle) {
    return (handle != NULL_HANDLE &&
            status[handle] != STATUS_EXCEPTION) ?
        entries[handle] : null;
}

private static final byte STATUS_OK = 1;
private static final byte STATUS_UNKNOWN = 2;
private static final byte STATUS_EXCEPTION = 3;