Static collection dictionary in WCF

Question

I am writing tracing class to find the execution time of modules/methods. I have a class like this

public class Trace
    {
        static Dictionary<string, Stopwatch> watches = null;

        static Trace()
        {
            Dictionary<string, Stopwatch> watches = new Dictionary<string, Stopwatch>();
        }

        public static void Start(string key, string losgMessage)
        {
            try
            {
                if (!watches.Keys.Contains(key))
                {
                    Stopwatch watch = new Stopwatch();
                    watch.Start();
                    watches.Add(key, watch);
                }
            }
            catch
            {
            }
        }

        public static void Stop(string key, Object logMessage, string sessionId)
        {
            try
            {

                if (!watches.Keys.Contains(key))
                {
                    Stopwatch watch = watches[key];
                    watch.Stop();
                    //log goes here
                }
            }
            catch
            {
            }
        }
    }

since wcf is multithreaded environment and the 'watches' static variable scope is application level, If some one(new rqst from the differnt client) tries to execute the same method with same key i will not consider it and trace it. So what would be the best option in this case. Any suggestion would be helpful.

edit : I am current appending sessionId with key. Cant i resolve this issue without session id

From the looks of it you also have a `sessionId`, wouldn't it be more reliable to perhaps append this to the function key to make it unique? — James, Sep 17 '12 at 12:21
Also, you need [locks](http://msdn.microsoft.com/de-de/library/c5kehkcz(v=vs.80).aspx) in the Start and Stop methods, because they are reading/writing the dictionary while other threads might be working on it at the same time. — Wutz, Sep 17 '12 at 12:23
I trust you don't plan to use this with any recursive methods. — hatchet - done with SOverflow, Sep 17 '12 at 12:24
"*yes I am currently doing so*" - If that's the case then there should be no issues with duplicate entries - assuming all requests have unique session ids that is. — James, Sep 17 '12 at 12:26
Why not just use a free profiler? You should also be aware that Stopwatch measures elapsed clock time, not CPU time. — hatchet - done with SOverflow, Sep 17 '12 at 12:29

score 1 · Accepted Answer · answered Sep 17 '12 at 12:34

1

Can't I resolve this issue without session Id

From the information provided, I would say no. If you have concurrent requests executing the same function call then you are going to get duplicate entries. The only way to avoid this is to ensure all keys are unique. I actually think using the session ID is required anyway, otherwise how can you map the function to the request?

Also, Dictionary isn't thread-safe (at least for writes), I would recommend using a ConcurrentDictionary.

answered Sep 17 '12 at 12:34

James

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if i use ConcurrentDictionary, dont i need to use lock before add/retreive/remove in ordinary dictionary? – Al. Sep 17 '12 at 12:41
"*don't I need to use lock before add/retrieve/remove*" - no, `ConcurrentDictionary` is thread-safe therefore can be accessed directly from multiple threads, all the locking is handled internally. – James Sep 17 '12 at 12:49
1

http://stackoverflow.com/questions/1949131/net-dictionary-locking-vs-concurrentdictionary -> Mark Byers claims it still needs lock. isnt it so – Al. Sep 17 '12 at 12:52
The point Mark Byers is making about race conditions e.g. you call `Contains` on the collection to check for a duplicate key, you then attempt to add that key if it doesn't exist. However, a concurrent thread could have added the same key inbetween calls. In your scenario, you don't have any reason to do this as all your keys will be unique. Also, `ConcurrentDictionary` has methods to avoid that sort of issue - [GetOrAdd](http://msdn.microsoft.com/en-us/library/ee378674.aspx) – James Sep 17 '12 at 13:00
thanks a lot.let me remove my lock and use ConcurrentDictionary – Al. Sep 17 '12 at 13:04
Just to clarify, the only thing you need to worry about is concurrent access to the collection, which `ConcurrentDictionary` should handle for you. Hope that helps. – James Sep 17 '12 at 13:07

Static collection dictionary in WCF

1 Answers1