String Interning: The Garbage Collectible way

Since I know people will want the actual implementation, here is a simple way of handling string interning in a way that will allow you to GC the results at some point. The issue is simple, I want to intern strings (so a string value is only held once through my entire app), but I don’t want to be stuck with them if the profiler state has been clear, for example.

public class GarbageCollectibleStringInterning
{
    private static IDictionary<string,string> strings = new Dictionary<string,string>();

    private static ReaderWriterLockSlim locker = new ReaderWriterLockSlim();
    
    public static void Clear()
    {
        locker.EnterWriteLock();
        try
        {
            strings.Clear();
        }
        finally
        {
            locker.ExitWriteLock();
        }
    }
    
    public static string Intern(string str)
    {
        string val;
        
        locker.EnterReadLock();
        try
        {
            if(strings.TryGetValue(str, out val))
                return val;
        }
        finally
        {
            locker.ExitReadLock();
        }
        
        locker.EnterWriteLock();
        try
        {
            if(strings.TryGetValue(str, out val))
                return val;
                
            strings.Add(str,str);
            return str;
        }
        finally
        {
            locker.ExitWriteLock();
        }
    }
}

This is a fairly simple implementation, a more complex one may try to dynamically respond to GC notification, but I think that this would be useful enough on its own.

Using this approach, I was able to reduce used memory in the profiler by over 50%. I gave up on that approach, however, because while it may reduce the memory footprint, it doesn't actually solve the problem, only delay it.

Print | posted on Sunday, December 27, 2009 12:00 PM