MemoryCache get in Disposed state Magically

Question

I did many tests, my MemoryCache instances get disposed after some time and always returns null when I call Get method. I think that is after PollingInterval.

To simulate you can start a new webapp and write this code:

    private static MemoryCache mem = new MemoryCache("MyCache");
    protected void Page_Load(object sender, EventArgs e)
    {
        string key = "MyKey";
        mem.Set(key, "MyValue", new CacheItemPolicy() {AbsoluteExpiration = DateTimeOffset.Now.AddDays(1), Priority = CacheItemPriority.NotRemovable});
        LtrValue.Text = mem.Get(key) as string;
    }

I configured the PollingInterval to 30 hours an seems to work.

I thought could be the AppDomain Unload, but after some investigation I don´t think that is it:

1-) MSDN says to use MemoryCache for ASP.NET: http://msdn.microsoft.com/en-us/library/ff477235(v=vs.100).aspx And says that ASP.NET 4 cache is built with ObjectCache:

In ASP.NET 4, caching is implemented by using the ObjectCache class.

2-) AppDomain unload would reset statics variable, creating new MemoryCache instances.

3-) I attached a event to AppDomain Unload like the MemoryCache does(I saw the decompiled source) in my test it wasn´t called and memorycache get disposed.

References:

The same post at MSDN forum: http://social.msdn.microsoft.com/Forums/en/netfxbcl/thread/1233ffb3-6480-431b-94ca-1190f96cf5f6

http://social.msdn.microsoft.com/Forums/en/netfxbcl/thread/0a666d5e-9bda-47bd-8dd3-98d32eb5fe60

MemoryCache Empty : Returns null after being set

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Answer 1

Its really a bug, it was fixed in .NET 4.5 and they are working to back-port to .NET 4

http://social.msdn.microsoft.com/Forums/en-US/netfxbcl/thread/1233ffb3-6480-431b-94ca-1190f96cf5f6/