It is essential that you mark your StreamInsight adapter configuration classes with either the [Serializable()] or [DataContract()] attributes. Keep in mind that the StreamInsight engine can be run either in process or remotely … and, if remote, these classes will have to be serialized on the wire. The serializable attribute is easier, but the DataContract attribute - through the [DataMember()] and the [IgnoreDataMember()] attributes - allows you to be more explicit in specifying which members actually go on the wire. I looked (quickly) and didn’t see this document but that doesn’t mean that it isn’t.
Now … what can happen if you don’t do this? Bad things. This happened to me yesterday and simply reinforced why I shave my head (so I can’t rip my hair out). So … everything had been working fine. I was making some changes to an adapter to try to resolve a Heisenbug caused by a race condition during the adapter tear down (I’ll discuss some of these challenges later, I think). When I went to run to test, I started running into exceptions when starting the query. It was an XmlException with the message:
Name cannot begin with the '<' character, hexadecimal value 0x3C.
Huh? I checked through everything and there were no members that began with a “<”. In fact, the C# compiler won’t let you do this, even if you use the “@” character (rightfully so … I mean, why on earth would you do that??). Examining the full stack trace, I could see that it was happening during the stream creation while serializing something. Once I loaded the debug symbols, I found that the offending member name was “<LogName>k__BackingField”, which certainly does begin with a “<”. Of course, there was no member that I declared in the code … there’s no way that I would even try to declare such a thing. It turns out, however, that the C# compiler will declare the backing fields for automatic properties like this and, for some reason, it chose yesterday to start blowing up on me. I finally found that the configuration class for a specific adapter was not marked as serializable (and I know better than this) and, once I changed it, all worked just fine.
I gotta tell you, I do so hate these mysterious errors.