全局对象的不一致持久性

我正在研究云托管的ZipFile创建服务。

这是一个跨域WebApi2服务，用于从不能承载任何服务器端代码的文件系统中提供ZipFiles。

基本操作如下:

• 用户使用与文件位置相关的url的string[]发出POST请求
WebApi将数组读入内存，并创建一个票号WebApi将票号返回给用户AJAX回调，然后重定向用户到一个web地址与附加的票号，它返回压缩文件在HttpResponseMessage

为了处理票据系统，我的设计方法是建立一个全局字典，该字典将随机生成的10位数字配对为List<String>值，并将字典配对为Queue，每次存储10,000个条目。(参考这里)

部分原因是WebApi不支持缓存

当我在本地进行AJAX调用时，它100%有效。当我远程打电话时，大约20%的时间是正常的。

当它失败时，我得到以下错误:

The given key was not present in the dictionary.

意思是在全局字典对象中找不到票号。

在过去的几个月里，我已经实现了相当多的Lazy singleton，而且我从来没有遇到过这种情况。

我哪里做错了?

//Initital POST request, sent to the service with the string[]
public string Post([FromBody]string value)
{
    try
    {
        var urlList = new JavaScriptSerializer().Deserialize<List<string>>(value);
        var helper = new Helper();
        var random = helper.GenerateNumber(10);
        CacheDictionary<String, List<String>>.Instance.Add(random, urlList);
        return random;
    }
    catch (Exception ex)
    {
        return ex.Message;
    }
}
//Response, cut off where the error occurs
public async Task<HttpResponseMessage> Get(string id)
{
    try
    {
        var urlList = CacheDictionary<String, List<String>>.Instance[id];
    }
    catch (Exception ex)
    {
        var response = new HttpResponseMessage(HttpStatusCode.InternalServerError)
        {
            Content = new StringContent(ex.Message)
        };
        return response;
    }
}
//CacheDictionary in its Lazy Singleton form:
public class CacheDictionary<TKey, TValue>
{
    private Dictionary<TKey, TValue> dictionary;
    private Queue<TKey> keys;
    private int capacity;
    private static readonly Lazy<CacheDictionary<String, List<String>>> lazy =
        new Lazy<CacheDictionary<String, List<String>>>(() => new CacheDictionary<String, List<String>>(10000));
    public static CacheDictionary<String, List<String>> Instance { get { return lazy.Value; } }
    private CacheDictionary(int capacity)
    {
        this.keys = new Queue<TKey>(capacity);
        this.capacity = capacity;
        this.dictionary = new Dictionary<TKey, TValue>(capacity);
    }
    public void Add(TKey key, TValue value)
    {
        if (dictionary.Count == capacity)
        {
            var oldestKey = keys.Dequeue();
            dictionary.Remove(oldestKey);
        }
        dictionary.Add(key, value);
        keys.Enqueue(key);
    }
    public TValue this[TKey key]
    {
        get { return dictionary[key]; }
    }
}

更多错误详情

at System.Collections.Generic.Dictionary`2.get_Item(TKey key)
at ZipperUpper.Models.CacheDictionary`2.get_Item(TKey key)