Intermittent errors while de-serializing object from XML

Question

I have a program that takes objects stored as XML in a database (basicly a message queue) and de-serializes them. Intermittently, I will get one of the following errors:

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Answer 1

XmlSerializer is supposed to be thread safe.

Even if that's the case, you can notice the behavior you are getting is in both cases failing at: XmlSerializer..ctor(Type type)

Given that, it seriously look like a multi-threading limitation trying to create serializers.

I suggest to take this code you have:

public XmlSerializer GetSerializer(Type t) {
        if (!SerializerCache.ContainsKey(t.FullName)) {
            SerializerCache.Add(t.FullName, new XmlSerializer(t)); // Error occurs here, intermittently
        }
        return SerializerCache[t.FullName];
    }

And implement a lock on the Add. This way you are only creating 1 serializer at a time. The hit is small if you aren't processing tons of different types.

Note that you need the lock anyway, as the way it is you could get duplicate exceptions when 2 types try to be added at the same time.

static object serializerCacheLock = new object();
public XmlSerializer GetSerializer(Type t) {
        if (!SerializerCache.ContainsKey(t.FullName))
        lock(serializerCacheLock)
        if (!SerializerCache.ContainsKey(t.FullName)) {
            SerializerCache.Add(t.FullName, new XmlSerializer(t));
        }
        return SerializerCache[t.FullName];
    }

If the above still isn't enough, I'd try with a read/write lock on serializer constructor vs. serializers usage. Line of thought being that maybe the multi-threading issue is worth than 2 ctors running at the same time.

All above is a Huge guess, but if it were me I'd definitely confirm is not that.