class UnpaddedInternalThreadLocalMap {

    //ThreadLocal内部封装slowThreadLocalMap
    static final ThreadLocal<InternalThreadLocalMap> slowThreadLocalMap = new ThreadLocal<InternalThreadLocalMap>();

    //计数器
    static final AtomicInteger nextIndex = new AtomicInteger();

    /** Used by {@link FastThreadLocal} */
    Object[] indexedVariables;

    //成员变量
    // Core thread-locals
    int futureListenerStackDepth;
    int localChannelReaderStackDepth;
    Map<Class<?>, Boolean> handlerSharableCache;
    IntegerHolder counterHashCode;
    ThreadLocalRandom random;
    Map<Class<?>, TypeParameterMatcher> typeParameterMatcherGetCache;
    Map<Class<?>, Map<String, TypeParameterMatcher>> typeParameterMatcherFindCache;

    // String-related thread-locals
    StringBuilder stringBuilder;
    Map<Charset, CharsetEncoder> charsetEncoderCache;
    Map<Charset, CharsetDecoder> charsetDecoderCache;

    // ArrayList-related thread-locals
    ArrayList<Object> arrayList;

    UnpaddedInternalThreadLocalMap(Object[] indexedVariables) {
        this.indexedVariables = indexedVariables;
    }
}

//集成了UnpaddedInternalThreadLocalMap
//内部包含了一个静态的threadlocal类slowThreadLocalMap和一些数据结构
public final class InternalThreadLocalMap extends UnpaddedInternalThreadLocalMap {

    private static final InternalLogger logger = InternalLoggerFactory.getInstance(InternalThreadLocalMap.class);

    private static final int DEFAULT_ARRAY_LIST_INITIAL_CAPACITY = 8;
    private static final int STRING_BUILDER_INITIAL_SIZE;
    private static final int STRING_BUILDER_MAX_SIZE;

    public static final Object UNSET = new Object();

    private BitSet cleanerFlags;

    static {
        STRING_BUILDER_INITIAL_SIZE =
                SystemPropertyUtil.getInt("io.netty.threadLocalMap.stringBuilder.initialSize", 1024);
        logger.debug("-Dio.netty.threadLocalMap.stringBuilder.initialSize: {}", STRING_BUILDER_INITIAL_SIZE);

        STRING_BUILDER_MAX_SIZE = SystemPropertyUtil.getInt("io.netty.threadLocalMap.stringBuilder.maxSize", 1024 * 4);
        logger.debug("-Dio.netty.threadLocalMap.stringBuilder.maxSize: {}", STRING_BUILDER_MAX_SIZE);
    }

    //如果设置了就获取否则返回null
    public static InternalThreadLocalMap getIfSet() {
        //拿到当前线程
        Thread thread = Thread.currentThread();
        //如果是FastThreadLocalThread类型，则直接获取InternalThreadLocalMap对象
        if (thread instanceof FastThreadLocalThread) {
            return ((FastThreadLocalThread) thread).threadLocalMap();
        }
        //否则上ThreadLocal获取
        return slowThreadLocalMap.get();
    }

    //获取InternalThreadLocalMap对象，没有就创建一个
    public static InternalThreadLocalMap get() {
        Thread thread = Thread.currentThread();
        if (thread instanceof FastThreadLocalThread) {
            return fastGet((FastThreadLocalThread) thread);
        } else {
            return slowGet();
        }
    }

    private static InternalThreadLocalMap fastGet(FastThreadLocalThread thread) {
        //获取线程的成员变量threadLocalMap();
        InternalThreadLocalMap threadLocalMap = thread.threadLocalMap();
        //如果为空则创建一个新的设置到线程当中
        if (threadLocalMap == null) {
            thread.setThreadLocalMap(threadLocalMap = new InternalThreadLocalMap());
        }
        return threadLocalMap;
    }

    private static InternalThreadLocalMap slowGet() {
        //在ThreadLocal当中获取InternalThreadLocalMap对象
        ThreadLocal<InternalThreadLocalMap> slowThreadLocalMap = UnpaddedInternalThreadLocalMap.slowThreadLocalMap;
        InternalThreadLocalMap ret = slowThreadLocalMap.get();
        //如果为null则创建一个新的设置到ThreadLocal当中并返回
        if (ret == null) {
            ret = new InternalThreadLocalMap();
            slowThreadLocalMap.set(ret);
        }
        return ret;
    }

    //移除InternalThreadLocalMap
    public static void remove() {
        //获取当前线程
        Thread thread = Thread.currentThread();
        //如果是FastThreadLocalThread类型则直接把成员变量设置为null
        if (thread instanceof FastThreadLocalThread) {
            ((FastThreadLocalThread) thread).setThreadLocalMap(null);
        } else {
            //在ThreadLocal当中移除
            slowThreadLocalMap.remove();
        }
    }

    //在ThreadLocal当中移除
    public static void destroy() {
        slowThreadLocalMap.remove();
    }

    //计数器++
    public static int nextVariableIndex() {
        int index = nextIndex.getAndIncrement();
        //如果为负数说明已经++到Int的最大值
        if (index < 0) {
            //计数器-- 后抛出异常
            nextIndex.decrementAndGet();
            throw new IllegalStateException("too many thread-local indexed variables");
        }
        return index;
    }

    //获取最后一个变量的index
    public static int lastVariableIndex() {
        return nextIndex.get() - 1;
    }

    // Cache line padding (must be public)
    // With CompressedOops enabled, an instance of this class should occupy at least 128 bytes.
    public long rp1, rp2, rp3, rp4, rp5, rp6, rp7, rp8, rp9;

    //构造参数 传入32个长度的数组里面全部都是相同的object引用
    private InternalThreadLocalMap() {
        super(newIndexedVariableTable());
    }

    //创建一个32长队数组，里面全部引用一个相同的object对象
    private static Object[] newIndexedVariableTable() {
        Object[] array = new Object[32];
        Arrays.fill(array, UNSET);
        return array;
    }

    //统计数量
    public int size() {
        int count = 0;

        if (futureListenerStackDepth != 0) {
            count ++;
        }
        if (localChannelReaderStackDepth != 0) {
            count ++;
        }
        if (handlerSharableCache != null) {
            count ++;
        }
        if (counterHashCode != null) {
            count ++;
        }
        if (random != null) {
            count ++;
        }
        if (typeParameterMatcherGetCache != null) {
            count ++;
        }
        if (typeParameterMatcherFindCache != null) {
            count ++;
        }
        if (stringBuilder != null) {
            count ++;
        }
        if (charsetEncoderCache != null) {
            count ++;
        }
        if (charsetDecoderCache != null) {
            count ++;
        }
        if (arrayList != null) {
            count ++;
        }

        for (Object o: indexedVariables) {
            if (o != UNSET) {
                count ++;
            }
        }

        // We should subtract 1 from the count because the first element in 'indexedVariables' is reserved
        // by 'FastThreadLocal' to keep the list of 'FastThreadLocal's to remove on 'FastThreadLocal.removeAll()'.
        return count - 1;
    }

    //返回StringBuilder
    public StringBuilder stringBuilder() {
        StringBuilder sb = stringBuilder;
        if (sb == null) {
            //没有则新创建一个返回 STRING_BUILDER_INITIAL_SIZE=初始容量
            return stringBuilder = new StringBuilder(STRING_BUILDER_INITIAL_SIZE);
        }

        //如果之前存在sb， 则判断容量是否 大于 STRING_BUILDER_MAX_SIZE
        if (sb.capacity() > STRING_BUILDER_MAX_SIZE) {

            //长度设置为初始容量
            sb.setLength(STRING_BUILDER_INITIAL_SIZE);
            sb.trimToSize();
        }
        //把长度设置为0，相当于清空sb
        sb.setLength(0);
        return sb;
    }


    //返回Map<Charset, CharsetEncoder>没有则创建
    public Map<Charset, CharsetEncoder> charsetEncoderCache() {
        Map<Charset, CharsetEncoder> cache = charsetEncoderCache;
        if (cache == null) {
            charsetEncoderCache = cache = new IdentityHashMap<Charset, CharsetEncoder>();
        }
        return cache;
    }

    //返回Map<Charset, CharsetDecoder>没有则创建
    public Map<Charset, CharsetDecoder> charsetDecoderCache() {
        Map<Charset, CharsetDecoder> cache = charsetDecoderCache;
        if (cache == null) {
            charsetDecoderCache = cache = new IdentityHashMap<Charset, CharsetDecoder>();
        }
        return cache;
    }

    public <E> ArrayList<E> arrayList() {
        return arrayList(DEFAULT_ARRAY_LIST_INITIAL_CAPACITY);
    }

   //返回一个minCapacity大小的list
    @SuppressWarnings("unchecked")
    public <E> ArrayList<E> arrayList(int minCapacity) {
        ArrayList<E> list = (ArrayList<E>) arrayList;
        if (list == null) {
            arrayList = new ArrayList<Object>(minCapacity);
            return (ArrayList<E>) arrayList;
        }
        list.clear();
        list.ensureCapacity(minCapacity);
        return list;
    }

    public int futureListenerStackDepth() {
        return futureListenerStackDepth;
    }

    public void setFutureListenerStackDepth(int futureListenerStackDepth) {
        this.futureListenerStackDepth = futureListenerStackDepth;
    }

    //获得线程的Random对象
    public ThreadLocalRandom random() {
        ThreadLocalRandom r = random;
        if (r == null) {
            random = r = new ThreadLocalRandom();
        }
        return r;
    }

    public Map<Class<?>, TypeParameterMatcher> typeParameterMatcherGetCache() {
        Map<Class<?>, TypeParameterMatcher> cache = typeParameterMatcherGetCache;
        if (cache == null) {
            typeParameterMatcherGetCache = cache = new IdentityHashMap<Class<?>, TypeParameterMatcher>();
        }
        return cache;
    }

    public Map<Class<?>, Map<String, TypeParameterMatcher>> typeParameterMatcherFindCache() {
        Map<Class<?>, Map<String, TypeParameterMatcher>> cache = typeParameterMatcherFindCache;
        if (cache == null) {
            typeParameterMatcherFindCache = cache = new IdentityHashMap<Class<?>, Map<String, TypeParameterMatcher>>();
        }
        return cache;
    }

    public IntegerHolder counterHashCode() {
        return counterHashCode;
    }

    public void setCounterHashCode(IntegerHolder counterHashCode) {
        this.counterHashCode = counterHashCode;
    }

    public Map<Class<?>, Boolean> handlerSharableCache() {
        Map<Class<?>, Boolean> cache = handlerSharableCache;
        if (cache == null) {
            // Start with small capacity to keep memory overhead as low as possible.
            handlerSharableCache = cache = new WeakHashMap<Class<?>, Boolean>(4);
        }
        return cache;
    }

    public int localChannelReaderStackDepth() {
        return localChannelReaderStackDepth;
    }

    public void setLocalChannelReaderStackDepth(int localChannelReaderStackDepth) {
        this.localChannelReaderStackDepth = localChannelReaderStackDepth;
    }

    public Object indexedVariable(int index) {
        Object[] lookup = indexedVariables;
        return index < lookup.length? lookup[index] : UNSET;
    }

    /**
     * @return {@code true} if and only if a new thread-local variable has been created
     */
    //存储对象
    public boolean setIndexedVariable(int index, Object value) {
        //对象数组
        Object[] lookup = indexedVariables;
        //判断下标小于数组长度
        if (index < lookup.length) {
            //拿出旧值
            Object oldValue = lookup[index];
            //设置新值
            lookup[index] = value;
            //判断oldValue == UNSET第一次设置
            return oldValue == UNSET;
        } else {
            //下标大于数组长度需要扩容
            expandIndexedVariableTableAndSet(index, value);
            return true;
        }
    }

    private void expandIndexedVariableTableAndSet(int index, Object value) {
        Object[] oldArray = indexedVariables;
        //旧数组长度
        final int oldCapacity = oldArray.length;
        //根据index扩容
        int newCapacity = index;
        newCapacity |= newCapacity >>>  1;
        newCapacity |= newCapacity >>>  2;
        newCapacity |= newCapacity >>>  4;
        newCapacity |= newCapacity >>>  8;
        newCapacity |= newCapacity >>> 16;
        newCapacity ++;

        //把旧数组拷贝到新数组
        Object[] newArray = Arrays.copyOf(oldArray, newCapacity);
        //其余位置全部设置为UNSET
        Arrays.fill(newArray, oldCapacity, newArray.length, UNSET);
        //设置值
        newArray[index] = value;
        //更新成员变量
        indexedVariables = newArray;
    }

    //移除对象
    public Object removeIndexedVariable(int index) {
        Object[] lookup = indexedVariables;
        if (index < lookup.length) {
            Object v = lookup[index];
            lookup[index] = UNSET;
            return v;
        } else {
            return UNSET;
        }
    }

    public boolean isIndexedVariableSet(int index) {
        Object[] lookup = indexedVariables;
        return index < lookup.length && lookup[index] != UNSET;
    }

    public boolean isCleanerFlagSet(int index) {
        return cleanerFlags != null && cleanerFlags.get(index);
    }

    public void setCleanerFlag(int index) {
        if (cleanerFlags == null) {
            cleanerFlags = new BitSet();
        }
        cleanerFlags.set(index);
    }
}