CODEWITHSUNDEEP
c#cachinglocking
Michel
Michel

Reputation: 23645

How to implement locking in a shared cachecontroller?

I have a static class which handles the cache read/write for frequently used data.

The code is this:

 public static T GetFromCache<T>(double seconds, string cacheId, Func<T> method) where T : class
    {
        HttpContext ctx = HttpContext.Current;
        object temp = null;
        temp = ctx.Cache[cacheId];

        if (temp == null)
        {
            lock (Sync)
            {
                temp = ctx.Cache[cacheId];
                if (temp == null)
                {
                    temp = method.Invoke();
                    AddToCache(temp as T, seconds, cacheId);
                    return temp as T;
                }

            }
        }

        if (temp is T)
        {
            return (T)temp;
        }
        return null;
    }

The code is used by various callers to read data from and write data to the cache. Now I have a Sync object (private static readonly object Sync = new object();) which gets locked when data gets written to the cache.

As this code is called by multiple callers, I would like to create a List of Sync objects, one for each caller. (with caller I don't mean the user, but calling code. I then would identify a caller by the signature of the parameter method) The reason I want this is that every piece of calling code can have it's own lock object; otherwise (I think) every call to this cachecontroller from different callers will use the same lock object. Then, the caching for the list of countries will also lock the caching of the list of states, and with two different lock objects, they will not be in each others way.

I would then use the CacheItemRemovedCallback method to remove the lockitems from the list.

The question is this: How can I do that?

Upvotes: 0

Views: 44

Answers (1)

Kajal Sinha
Kajal Sinha

Reputation: 1575

By having one Sync object for each user will defy the purpose of synchronization as each use will hold its own lock and there will be a chance that for the same cacheId you will end up invoking the method multiple times. This might result in data becoming inconsistent.

If you wish to keep one Sync object per user then it's good to make use of session variables or per user cache or something similar.. otherwise each user will virtually end up messing up with each other's cacheId results.

If you have a scenario when there can be Multiple readers of data but at a time a single user can write it then try using ReaderWriterLockSlim. This is very fast compared to lock in a multi user scenario.

Update1

Considering the cacheId is unique and not common among the callers. You can use the following code.

No lock is needed here. Reason, HttpContext.Cache is ThreadSafe. Meaning, you can read/save values to Cache. But, if the value reference itself is being shared among more than one concurrent calls, then please synchronize it.

 public static T GetFromCache<T>(double seconds, string cacheId, Func<T> method) where T : class
        {
            HttpContext ctx = HttpContext.Current;
            object temp = null;
            temp = ctx.Cache[cacheId];
            if (temp == null)
            {
                temp = method.Invoke();
                AddToCache(temp as T, seconds, cacheId);
                return temp as T;
            }
        }

Regards

Upvotes: 1

Related Questions