Do closures break serialization

问题

Today I faced a SerializationException that refered to some anonymous inner class +<>c__DisplayClass10 stating it was not serializable, when IIS tried to store the session in the ASP.NET State Service:

Type 'Xyz.GeneralUnderstandingTests+ASerializableType+<>c__DisplayClass10' in Assembly 'Xyz, Version=1.2.5429.24450, Culture=neutral, PublicKeyToken=null' is not marked as serializable.

I looked for lambdas in my code and found quite a few, but most of them were not new and did never have any issues in serialization. But then I noticed that I had built in a new lambda expression that "happened" to build up a closure.

Searching Stackoverflow for closure serialization I found some Q&As that reveal that closures cannot be serialized in other languages such as PHP *) but I did not manage to find such a statement for C#. I have however been able to build a very simple example that seems to confirm that closures are not serializable whereas "normal" functions are

[TestFixture]
public class GeneralUnderstandingTests
{
    [Serializable]
    private class ASerializableType
    {
        private readonly Func<int> thisIsAClosure;
        private readonly Func<int> thisIsNotAClosure;

        public ASerializableType()
        {
            const int SomeConst = 12345;
            thisIsNotAClosure = () => SomeConst; // succeeds to serialize

            var someVariable = 12345;
            thisIsAClosure = () => someVariable; // fails to serialize
        }
    }

    [Test]
    public void ASerializableType_CanBeSerialized()
    {
        var sessionStateItemCollection = new 
            System.Web.SessionState.SessionStateItemCollection();
        sessionStateItemCollection["sut"] = new ASerializableType();
        sessionStateItemCollection.Serialize(new BinaryWriter(new MemoryStream()));
    }
}

This test fails but goes green as soon as the line thisIsAClosure = ... is commented out. The line thisIsNotAClosure = ... however does not cause any issues as SomeConst is not a variable but a constant, that is, it does not build a closure but is inlined by the compiler.

Can you confirm that what I have concluded is correct?

=> Is there a way to circumvent this issue?

=> Could it be that this depends on the internals of the compiler used? Since it is the compiler that turns the lambda/closure expression into a anonymous inner class.

*) Links:

Exception: Serialization of 'Closure' is not allowed
Closures Can't Be Serialized, How To Do Callbacks via AJAX to PHP?
Serialization of 'Closure' is not allowed with php pthreads
How to serialize object that has closures inside properties?

来源：https://stackoverflow.com/questions/26887460/do-closures-break-serialization

标签

serialization

lambda

closures