.net源码研究（1）HashTable

HashTable构造函数源码如下：

public Hashtable(int capacity, float loadFactor)
{
    if (capacity < 0)
    {
        throw new ArgumentOutOfRangeException("capacity", Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
    }
    if ((loadFactor < 0.1f) || (loadFactor > 1f))
    {
        throw new ArgumentOutOfRangeException("loadFactor", Environment.GetResourceString("ArgumentOutOfRange_HashtableLoadFactor", new object[] { 0.1, 1.0 }));
    }
    this.loadFactor = 0.72f * loadFactor;
    double num = ((float) capacity) / this.loadFactor;
    if (num > 2147483647.0)
    {
        throw new ArgumentException(Environment.GetResourceString("Arg_HTCapacityOverflow"));
    }
    int num2 = (num > 3.0) ? HashHelpers.GetPrime((int) num) : 3;
    this.buckets = new bucket[num2];
    this.loadsize = (int) (this.loadFactor * num2);
    this.isWriterInProgress = false;
}

 

HashTable实质为一个一维数组，即上述源码中的buckets，其初始大小num2由初始指定容量capacity和装载因子loadFactor决定,其实际装载容量loadsize为装在因子*0.72f*初始大小num2。

注：

• capacity: System.Collections.Hashtable 对象最初可包含的元素的近似数目。

• loadFactor: 0.1 到 1.0 范围内的数字，再乘以提供最佳性能的默认值。结果是元素与存储桶的最大比率。

Insert方法源码如下：

[ReliabilityContract(Consistency.WillNotCorruptState, Cer.MayFail)]
private void Insert(object key, object nvalue, bool add)
{
    uint num;
    uint num2;
    if (key == null)
    {
        throw new ArgumentNullException("key", Environment.GetResourceString("ArgumentNull_Key"));
    }
    if (this.count >= this.loadsize)
    {
        this.expand();
    }
    else if ((this.occupancy > this.loadsize) && (this.count > 100))
    {
        this.rehash();
    }
    uint num3 = this.InitHash(key, this.buckets.Length, out num, out num2);
    int num4 = 0;
    int index = -1;
    int num6 = (int) (num % this.buckets.Length);
Label_0071:
    if (((index == -1) && (this.buckets[num6].key == this.buckets)) && (this.buckets[num6].hash_coll < 0))
    {
        index = num6;
    }
    if ((this.buckets[num6].key == null) || ((this.buckets[num6].key == this.buckets) && ((this.buckets[num6].hash_coll & 0x80000000L) == 0L)))
    {
        if (index != -1)
        {
            num6 = index;
        }
        Thread.BeginCriticalRegion();
        this.isWriterInProgress = true;
        this.buckets[num6].val = nvalue;
        this.buckets[num6].key = key;
        this.buckets[num6].hash_coll |= (int) num3;
        this.count++;
        this.UpdateVersion();
        this.isWriterInProgress = false;
        Thread.EndCriticalRegion();
    }
    else if (((this.buckets[num6].hash_coll & 0x7fffffff) == num3) && this.KeyEquals(this.buckets[num6].key, key))
    {
        if (add)
        {
            throw new ArgumentException(Environment.GetResourceString("Argument_AddingDuplicate__", new object[] { this.buckets[num6].key, key }));
        }
        Thread.BeginCriticalRegion();
        this.isWriterInProgress = true;
        this.buckets[num6].val = nvalue;
        this.UpdateVersion();
        this.isWriterInProgress = false;
        Thread.EndCriticalRegion();
    }
    else
    {
        if ((index == -1) && (this.buckets[num6].hash_coll >= 0))
        {
            this.buckets[num6].hash_coll |= -2147483648;
            this.occupancy++;
        }
        num6 = (int) ((num6 + num2) % ((ulong) this.buckets.Length));
        if (++num4 < this.buckets.Length)
        {
            goto Label_0071;
        }
        if (index == -1)
        {
            throw new InvalidOperationException(Environment.GetResourceString("InvalidOperation_HashInsertFailed"));
        }
        Thread.BeginCriticalRegion();
        this.isWriterInProgress = true;
        this.buckets[index].val = nvalue;
        this.buckets[index].key = key;
        this.buckets[index].hash_coll |= (int) num3;
        this.count++;
        this.UpdateVersion();
        this.isWriterInProgress = false;
        Thread.EndCriticalRegion();
    }
}

 

当HashTable也即buckets数组中实际添加元素数超过loadsize时，会调用expand方法使得buckets扩容一倍。

根据要插入的key和buckets的length生成初次要插入的位置num6和发生哈希冲突后要增加的步进量num2，该计算由InitHash函数实现，源码如下：

private uint InitHash(object key, int hashsize, out uint seed, out uint incr)
{
    uint num = (uint) (this.GetHash(key) & 0x7fffffff);
    seed = num;
    incr = 1 + ((uint) (((seed >> 5) + 1) % (hashsize - 1)));
    return num;
}

 

 参见：http://www.cnblogs.com/xiaosuo/archive/2010/03/18/1632341.html