U3d内存优化（二）之Dictonary

1. 先看代码：

        public void Update()
        {
             DictionaryTest();
        }
        public void DictionaryTest()
        {
            if (!mBInited)
            {
                mBInited = true;
                m_States.Add(State.None, 0);
                m_States.Add(State.Start, 0);
                m_States.Add(State.Stop, 0);
            }

            int none = m_States[State.None];
        }

        private bool mBInited = false;
        Dictionary<State, int> m_States = new Dictionary<State, int>();
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2.运行结果（内存消耗）

3.原因分析
先看Dictionary

[__DynamicallyInvokable]
public TValue this[TKey key]
{
    [__DynamicallyInvokable]
    get
    {
        int num = this.FindEntry(key);
        if (num >= 0)
        {
            return this.entries[num].value;
        }
        ThrowHelper.ThrowKeyNotFoundException();
        return default(TValue);
    }
    [__DynamicallyInvokable, TargetedPatchingOptOut("Performance critical to inline this type of method across NGen image boundaries")]
    set
    {
        this.Insert(key, value, false);
    }
}
// System.Collections.Generic.Dictionary<TKey, TValue>
private int FindEntry(TKey key)
{
    if (key == null)
    {
        ThrowHelper.ThrowArgumentNullException(ExceptionArgument.key);
    }
    if (this.buckets != null)
    {
        int num = this.comparer.GetHashCode(key) & 2147483647;
        for (int i = this.buckets[num % this.buckets.Length]; i >= 0; i = this.entries[i].next)
        {
            if (this.entries[i].hashCode == num && this.comparer.Equals(this.entries[i].key, key))
            {
                return i;
            }
        }
    }
    return -1;
}
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最终的消耗是在 FindEntry(TKey key)中的this.comparer.GetHashCode(key)，而compare这个泛型函数会导致内存的分配涉及到反射typeof(Tkey)，

// System.Collections.Generic.Dictionary<TKey, TValue>
private IEqualityComparer<TKey> comparer;
ublic static Comparer<T> Default
{
    [__DynamicallyInvokable]
    get
    {
        Comparer<T> comparer = Comparer<T>.defaultComparer;
        if (comparer == null)
        {
            comparer = Comparer<T>.CreateComparer();
            Comparer<T>.defaultComparer = comparer;
        }
        return comparer;
    }
}

private static Comparer<T> CreateComparer()
{
    RuntimeType runtimeType = (RuntimeType)typeof(T);
    if (typeof(IComparable<T>).IsAssignableFrom(runtimeType))
    {
        return (Comparer<T>)RuntimeTypeHandle.CreateInstanceForAnotherGenericParameter((RuntimeType)typeof(GenericComparer<int>), runtimeType);
    }
    if (runtimeType.IsGenericType && runtimeType.GetGenericTypeDefinition() == typeof(Nullable<>))
    {
        RuntimeType runtimeType2 = (RuntimeType)runtimeType.GetGenericArguments()[0];
        if (typeof(IComparable<>).MakeGenericType(new Type[]
        {
            runtimeType2
        }).IsAssignableFrom(runtimeType2))
        {
            return (Comparer<T>)RuntimeTypeHandle.CreateInstanceForAnotherGenericParameter((RuntimeType)typeof(NullableComparer<int>), runtimeType2);
        }
    }
    return new ObjectComparer<T>();
}
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