具有基于时间的生命周期的单例

Question

我正在尝试实现一个类似单例的类，它的生命周期是基于时间的。程序开始后每 5 秒创建的实例应该是相同的，就像在正常的单例中一样，并且在不同的 5 秒跨度之间应该有不同的单例实例。我想出的是一个存储单例实例的列表，而不是典型的静态实例字段。但是，当我测试它时，我仍然得到相同的实例。代码如下：

class Program
    {
        static void Main(string[] args)
        {
            TimedSingleton t1 = TimedSingleton.Instance();
            Thread.Sleep(5500);
            TimedSingleton t2 = TimedSingleton.Instance();

        Console.WriteLine(t1 == t2);

        Console.ReadKey();
    }
}

class TimedSingleton
{
    private static ArrayList _instancesArrayList = new ArrayList();
    private static List<int> AddedPositions = new List<int>();

    private static DateTime _startTime = DateTime.Now;

    protected TimedSingleton()
    {
    }

    public static TimedSingleton Instance()
    {
        int index = (int) DateTime.Now.Subtract(_startTime).TotalSeconds%5;

        if (AddedPositions.Count == 0)
        {
            _instancesArrayList.Add(new TimedSingleton());
            AddedPositions.Add(index);
            return (TimedSingleton)_instancesArrayList[index];
        }

        if (AddedPositions.Contains(index))
        {
            return (TimedSingleton) _instancesArrayList[index];
        }

        AddedPositions.Add(index);
        _instancesArrayList.Add(new TimedSingleton());
        return (TimedSingleton) _instancesArrayList[index];
    }
}

结果：true

如何修复它以在每 5 秒的时间跨度内返回单独的实例？

Answer 1

我没有在列表和数组列表中摆弄索引，而是将您的实现更改为使用通用Dictionary<tkey, tvalue>，以便索引可以是一个简单的查找。请记住，这会不断添加项目，因此如果经常调用，您将耗尽内存。这里没有清理。

class TimedSingleton
{
    // have a dictonary to hold the seconds
    // and the instance so we can lookup
    private static Dictionary<int, TimedSingleton> AddedPositions = new Dictionary<int, TimedSingleton>();

    private static DateTime _startTime = DateTime.Now;

    protected TimedSingleton()
    {
    }

    public static TimedSingleton Instance()
    {
        // divide by 5
        int index = (int)DateTime.Now.Subtract(_startTime).TotalSeconds / 5;
        Debug.WriteLine(index);

        // 
        TimedSingleton result;
        // if you're going to multhreed this
        lock(AddedPositions)
        {
            // try to get the index seconds ...
            if (!AddedPositions.TryGetValue(index,out result))
            {
                // not happened
                Debug.WriteLine("Created new instance");
                result = new TimedSingleton();
                // store it for later
                AddedPositions.Add(index, result);
            }
            else
            {
                // result has now a previous instance
                Debug.WriteLine("from cache");
            }
        }
        return result;
    }
}