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Find the bugWhen you can't rely on your own identity
time to read 2 min | 234 words
We had a need to generate unique ids for connections in our db. We used the following code:
public class NotificationsClientConnection : IDisposable { private static int _counter = 0; private readonly WebSocket _webSocket; private readonly DocumentDatabase _documentDatabase; private readonly DateTime _startedAt; public NotificationsClientConnection(WebSocket webSocket, DocumentDatabase documentDatabase) { _webSocket = webSocket; _documentDatabase = documentDatabase; _startedAt = SystemTime.UtcNow; } public int Id => Interlocked.Increment(ref _counter); public TimeSpan Age => SystemTime.UtcNow - _startedAt; }
Do you see the bug? It is a subtle one.
When you are ready, peek below.
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The issue is in the following line:
public int Id => Interlocked.Increment(ref _counter);
The intent was to create a field that would be initialized on startup. Unfortunately, the usage of the lambda symbol "=>" instead of assignment "=" turned that into a computed property, which will return a new value on every call.
More posts in "Find the bug" series:
- (29 Feb 2016) When you can't rely on your own identity
- (05 Jan 2016) The case of the degrading system–Answer
- (04 Jan 2016) The case of the degrading system
- (11 Sep 2015) The concurrent memory buster
- (20 Apr 2011) Why do I get a Null Reference Exception?
- (25 Nov 2010) A broken tree
- (13 Aug 2010) RavenDB HiLo implementation
- (25 Jul 2010) Accidental code reviews
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