SpinLock and readonly fields

Question

Just reading through the MSDN page about new .NET 4.0 feature SpinLock and can not understand idea behind the following statement:

Do not store SpinLock instances in readonly fields.

My feelings that this is somehow related to value-type specifics but not sure how exactly and why. Could anybody bring more light on this point?

Answer 1

The underlying problem is that the C# compiler creates a copy of a readonly value type field when you call a non-static method on it and executes that method on the copy - because the method could have side effects that change the value of the struct - which is not allowed for readonly fields.

For further clarification see "Mutating Readonly Structs".