public class ThreadId {
    private static final AtomicInteger nextId = new AtomicInteger(0);
    private static final ThreadLocal<Integer> threadId = new ThreadLocal<Integer>() {
        @Override
        protected Integer initialValue() {
            return nextId.get();
        }
    };
    public static int get() {
        return threadId.get();
    }
}

public class Thread{
      private int id;
      public void setId(int id){
          this.id=id;
      }
}

public class Thread{
      private Map<String,Object> map;
     public Map<String,Object> getMap(){
         if(map==null)
            map=new HashMap<>();
         return map;
     }
}

   Thread.currentThread().getMap().put("id",id);
   Thread.currentThread().getMap().put("looper",looper);

  Looper looper=(Looper) Thread.currentThread().getMap().get("looper");

  public class ThreadLocal<T> {
    public void set(T value) {
        Thread t = Thread.currentThread();
         Map map = t.getMap();
        if (map != null)
           //以自己為鍵
            map.put(this, value);
        else
            createMap(t, value);
    }
    public T get() {
        Thread t = Thread.currentThread();
        Map<ThreadLocal<?>,T> map = t.getMap();
        if (map != null) {
            T e = map.get(this);
            return e;
        }
        return setInitialValue();
    }
}

   public void set(T value) {
        Thread t = Thread.currentThread();
        ThreadLocalMap map = getMap(t);
        if (map != null)
            map.set(this, value);
        else
            createMap(t, value);
    }

 ThreadLocalMap getMap(Thread t) {
        return t.threadLocals;
   }

public T get() {
        Thread t = Thread.currentThread();
        ThreadLocalMap map = getMap(t);
        if (map != null) {
            ThreadLocalMap.Entry e = map.getEntry(this);
            if (e != null) {
                @SuppressWarnings("unchecked")
                T result = (T)e.value;
                return result;
            }
        }
        return setInitialValue();
    }

private T setInitialValue() {
        T value = initialValue();
        Thread t = Thread.currentThread();
        ThreadLocalMap map = getMap(t);
        if (map != null)
            map.set(this, value);
        else
            createMap(t, value);
        return value;
    }

public void remove() {
         ThreadLocalMap m = getMap(Thread.currentThread());
         if (m != null)
             m.remove(this);
     }

  private final int threadLocalHashCode = nextHashCode();
 private static int nextHashCode() {
        return nextHashCode.getAndAdd(HASH_INCREMENT);
    }
  private static AtomicInteger nextHashCode =
        new AtomicInteger();
   private static final int HASH_INCREMENT = 0x61c88647;

  public class MagicHashCode {
      //ThreadLocal中定義的魔數(shù)
     private static final int HASH_INCREMENT = 0x61c88647;
     public static void main(String[] args) {
         hashCode(16);//初始化16
         hashCode(32);//2倍擴(kuò)容
         hashCode(64);
     }
    private static void hashCode(int length){         
        int hashCode = 0; 
         for(int i=0;i<length;i++){
            hashCode = i*HASH_INCREMENT+HASH_INCREMENT;
             System.out.print(hashCode & (length-1));//求取模后的下標(biāo)
             System.out.print(" ");
         }
         System.out.println();
     }
 }

       /**
         * 初始容量，必須是2的冪。這樣的話，方便把取模運(yùn)算轉(zhuǎn)化為與運(yùn)算， 
         * 效率高
         */
        private static final int INITIAL_CAPACITY = 16;
        /**
         * 容納Entry元素，長(zhǎng)度必須是2的冪
         */
        private Entry[] table;
        /**
         * table中的元素個(gè)數(shù).
         */
        private int size = 0;
        /**
         * table里的元素達(dá)到這個(gè)值就需要擴(kuò)容了
         * 其實(shí)是有個(gè)裝載因子的概念的
         */
        private int threshold; // Default to 0

  ThreadLocalMap(ThreadLocal<?> firstKey, Object firstValue) {
        table = new Entry[INITIAL_CAPACITY];
        int i = firstKey.threadLocalHashCode & (INITIAL_CAPACITY - 1);
        table[i] = new Entry(firstKey, firstValue);
        size = 1;
        setThreshold(INITIAL_CAPACITY);
  }

private void setThreshold(int len) {
          threshold = len * 2 / 3;
 }

 static class Entry extends WeakReference<ThreadLocal<?>> {
            Object value;
            Entry(ThreadLocal<?> k, Object v) {
                super(k);
                value = v;
            }
        }

 private void set(ThreadLocal<?> key, Object value) {
            Entry[] tab = table;
            int len = tab.length;
            int i = key.threadLocalHashCode & (len-1);
           //如果沖突的話，進(jìn)入該循環(huán)，向后探測(cè)
            for (Entry e = tab[i];
                 e != null;
                 e = tab[i = nextIndex(i, len)]) {
                ThreadLocal<?> k = e.get();
               //判斷鍵是否相等，相等的話只要更新值就好了
                if (k == key) {
                    e.value = value;
                    return;
                }
                if (k == null) {
                   //該Entry對(duì)應(yīng)的ThreadLocal已經(jīng)被回收，執(zhí)行replaceStaleEntry并返回
                    replaceStaleEntry(key, value, i);
                    return;
                }
            }
            tab[i] = new Entry(key, value);
            int sz = ++size;
            //進(jìn)行啟發(fā)式清理，如果沒有清理任何元素并且表的大小超過(guò)了閾值，需要擴(kuò)容并重哈希
            if (!cleanSomeSlots(i, sz) && sz >= threshold)
                rehash();
        }

private static int nextIndex(int i, int len) {
            return ((i + 1 < len) ? i + 1 : 0);
}

private void replaceStaleEntry(ThreadLocal<?> key, Object value,
                               int staleSlot) {
    Entry[] tab = table;
    int len = tab.length;
    Entry e;
    // 向前掃描到一個(gè)空的slot為止，找到離這個(gè)空slot最近的無(wú)效slot，記錄為slotToExpunge
    int slotToExpunge = staleSlot;
    for (int i = prevIndex(staleSlot, len);
         (e = tab[i]) != null;
         i = prevIndex(i, len)) {
        if (e.get() == null) {
            slotToExpunge = i;
        }
    }
    // 向后遍歷table
    for (int i = nextIndex(staleSlot, len);
         (e = tab[i]) != null;
         i = nextIndex(i, len)) {
        ThreadLocal<?> k = e.get();
        // 找到了key，將其與無(wú)效slot交換
        if (k == key) {
            // 更新對(duì)應(yīng)slot的value值
            e.value = value;
            tab[i] = tab[staleSlot];
            tab[staleSlot] = e;
            //如果之前還沒有探測(cè)到過(guò)其他無(wú)效的slot
            if (slotToExpunge == staleSlot) {
                slotToExpunge = i;
            }
            // 從slotToExpunge開始做一次連續(xù)段的清理，再做一次啟發(fā)式清理
            cleanSomeSlots(expungeStaleEntry(slotToExpunge), len);
            return;
        }
        // 如果當(dāng)前的slot已經(jīng)無(wú)效，并且向前掃描過(guò)程中沒有無(wú)效slot，則更新slotToExpunge為當(dāng)前位置
        if (k == null && slotToExpunge == staleSlot) {
            slotToExpunge = i;
        }
    }
    // 如果key之前在table中不存在，則放在staleSlot位置
    tab[staleSlot].value = null;
    tab[staleSlot] = new Entry(key, value);
    // 在探測(cè)過(guò)程中如果發(fā)現(xiàn)任何其他無(wú)效slot，連續(xù)段清理后做啟發(fā)式清理
    if (slotToExpunge != staleSlot) {
        cleanSomeSlots(expungeStaleEntry(slotToExpunge), len);
    }
}

 private int expungeStaleEntry(int staleSlot) {
            Entry[] tab = table;
            int len = tab.length;
            // 刪除 staleSlot
            tab[staleSlot].value = null;
            tab[staleSlot] = null;
            size--;
            Entry e;
            int i;
            for (i = nextIndex(staleSlot, len);
                 (e = tab[i]) != null;
                 i = nextIndex(i, len)) {
                ThreadLocal<?> k = e.get();
                if (k == null) {
                    e.value = null;
                    tab[i] = null;
                    size--;
                } else {
                   //對(duì)元素進(jìn)行再散列
                    int h = k.threadLocalHashCode & (len - 1);
                    if (h != i) {
                        tab[i] = null;
                        while (tab[h] != null)
                            h = nextIndex(h, len);
                        tab[h] = e;
                    }
                }
            }
            return i;
        }

private boolean cleanSomeSlots(int i, int n) {
    boolean removed = false;
    Entry[] tab = table;
    int len = tab.length;
    do {
        // i在任何情況下自己都不會(huì)是一個(gè)無(wú)效slot，所以從下一個(gè)開始判斷
        i = nextIndex(i, len);
        Entry e = tab[i];
        if (e != null && e.get() == null) {
            // 擴(kuò)大掃描控制因子
            n = len;
            removed = true;
            // 清理一個(gè)連續(xù)段
            i = expungeStaleEntry(i);
        }
    } while ((n >>>= 1) != 0);
    return removed;
}

private void rehash() {
    // 全量清理
    expungeStaleEntries();
    //因?yàn)樽隽艘淮吻謇?，所以size可能會(huì)變小，這里的實(shí)現(xiàn)是調(diào)低閾值來(lái)判斷是否需要擴(kuò)容。 threshold默認(rèn)為len*2/3，所以這里的threshold - threshold / 4相當(dāng)于len/2。
    if (size >= threshold - threshold / 4) {
        resize();
    }
}

private void expungeStaleEntries() {
    Entry[] tab = table;
    int len = tab.length;
    for (int j = 0; j < len; j++) {
        Entry e = tab[j];
        if (e != null && e.get() == null) {
            expungeStaleEntry(j);
        }
    }
}

private void resize() {
    Entry[] oldTab = table;
    int oldLen = oldTab.length;
    int newLen = oldLen * 2;
    Entry[] newTab = new Entry[newLen];
    int count = 0;
    for (int j = 0; j < oldLen; ++j) {
        Entry e = oldTab[j];
        if (e != null) {
            ThreadLocal<?> k = e.get();
            if (k == null) {
                e.value = null; 
            } else {
                // 擴(kuò)容后要重新放置元素
                int h = k.threadLocalHashCode & (newLen - 1);
                while (newTab[h] != null) {
                    h = nextIndex(h, newLen);
                }
                newTab[h] = e;
                count++;
            }
        }
    }
    setThreshold(newLen);
    size = count;
    table = newTab;
}

private Entry getEntry(ThreadLocal<?> key) {
    int i = key.threadLocalHashCode & (table.length - 1);
    Entry e = table[i];
    // 對(duì)應(yīng)的entry存在且key未被回收
    if (e != null && e.get() == key) {
        return e;
    } else {
        // 繼續(xù)往后查找
        return getEntryAfterMiss(key, i, e);
    }
}
private Entry getEntryAfterMiss(ThreadLocal<?> key, int i, Entry e) {
    Entry[] tab = table;
    int len = tab.length;
    // 不斷向后探測(cè)直到遇到空entry
    while (e != null) {
        ThreadLocal<?> k = e.get();
        // 找到
        if (k == key) {
            return e;
        }
        if (k == null) {
            // 該entry對(duì)應(yīng)的ThreadLocal實(shí)例已經(jīng)被回收，調(diào)用expungeStaleEntry來(lái)清理無(wú)效的entry
            expungeStaleEntry(i);
        } else {
            // 下一個(gè)位置
            i = nextIndex(i, len);
        }
        e = tab[i];
    }
    return null;
}

private void remove(ThreadLocal<?> key) {
    Entry[] tab = table;
    int len = tab.length;
    int i = key.threadLocalHashCode & (len - 1);
    for (Entry e = tab[i];
         e != null;
         e = tab[i = nextIndex(i, len)]) {
        if (e.get() == key) {
            //斷開弱引用
            e.clear();
            // 連續(xù)段清理
            expungeStaleEntry(i);
            return;
        }
    }
}