动态变量在内存不足时释放？

Question

背景

所以前提是我有一个用属性提供数据的类.

class ExampleClass
{
   string _largeCalculatedVariable = null;
   public string largeCalculatedVariable
   {
       get
       {
           if (_largeCalculatedVariable == null)
           {
              _largeCalculatedVariable = LongRunningCalculate();
           }
           return _largeCalculatedVariable
       }
   }
}

该属性隐藏了这样的事实:如果数据尚未生成,则数据可以即时计算数据,但如果之前已经预先计算或计算,则将返回缓存值.

问题

问题是可能会生成一个大的ExampleClass列表,如果我访问largeCalculatedVariable足够的它们,我可能会耗尽内存.既然我可以随时重新计算这个值是否有办法告诉.NET _largeCalculatedVariable何时需要内存？

注意:我有一种感觉,我可能在这里使用错误的设计模式.

Answer 1

如果您使用的是.NET 4.0或更新版本,您可以使用MemoryCache该类,您可以将其设置为具有应存储多少数据的规则,并且如果已达到其限制,它将自行清除以腾出空间.

class ExampleClass
{
   //This is a static constructor;
   static ExampleClass()
   {
       var settings = new NameValueCollection();
       settings.Add("PhysicalMemoryLimitPercentage", "75");

       _cache = new MemoryCache("ExampleClassCache", settings);
   }

   private static MemoryCache _cache;

   public ExampleClass()
   {
      _cacheKey = Guid.NewGuid().ToString();
   }

   private readonly string _cacheKey;

   public string largeCalculatedVariable
   {
       get
       {
            var record = _cache.Get(_cacheKey) as string;

            //If record was null that means the item was not in the cache.
            if(record == null)
            {
                record = LongRunningCalculate();
                _cache.Add(_cacheKey, record, new CacheItemPolicy(), null);
            }

           return record;
       }
   }
}

如果你想要,你也可以ExampleClass从缓存中取出物品,以便在处理对象时释放空间,实现起来并不多.

class ExampleClass : IDisposable
{
    //...Everything else is the same from the previous code example.

    public void Dispose()
    {
        Dispose(true)
        GC.SupressFinialize(this);
    }

    bool _disposed;

    protected virtual void Dispose(bool disposing)
    {
        if(!_disposed)
        {
            if(disposing)
            {
                //Nothing to do here, we want to remove from the cache if Dispose or the finalizer is called.
                //But you may have IDisposeable objects in your real class, they should be disposed in here.
            }

            if(_cacheKey != null)
                _cache.Remove(_cacheKey, null);

            _disposed = true;
        }
    }

    ~ExampleClass()
    {
        Dispose(false);
    }
}