Who can cancel Carmen Sandiego?
time to read 2 min | 218 words

RavenDB is a pretty big system, with well over 1 million lines of code. Recently, I had to deal with an interesting problem. I had a CancellationToken at hand, which I expected to remain valid for the duration of the full operation.

However, something sneaky was going on there. Something was cancelling my CancelationToken, and not in an expected manner. At last count, I had roughly 2 bazillion CancelationTokens in the RavenDB codebase. Per request, per database, global to the server process, time-based, operation-based, etc., etc.

Figuring out why the CancelationToken was canceled turned out to be a chore. Instead of reading through the code, I cheated.

token.Register(() =>
{
    Console.WriteLine("Cancelled!" + Environment.StackTrace);
});

I ran the code, tracked back exactly who was calling cancel, and realized that I had mixed the request-based token with the database-level token. A single line fix in the end. Until I knew where it was, it was very challenging to figure it out.

This approach, making the code tell you what is wrong, is an awesome way to cut down debugging time by a lot.

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