provider class singleton not thread safe

[trystanc]

The singleton pattern is used in the provider classes to return an instance of the class.

This implementation of singleton does not seem to be thread safe. Is this taken care of in another way by ASP.NET or is it just not thread safe?


For an example of a thread safe singleton in C# see http://www.yoda.arachsys.com/csharp/singleton.html

[jimibt]

trystanc - that's a crackin good read. i really will take this to heart and try to benchmark/expose it's use within tbh.

verging on excellent 'foresight'....

jimi

http://www.originaltalent.com

[jimibt]

trystanc - had a play (haven't measured anything yet). here's how my ForumsProvider 'intro' looks now:

namespace MB.TheBeerHouse.DAL
{
    public abstract class ForumsProvider : DataAccess
    {
        static private readonly ForumsProvider _instance = (ForumsProvider)Activator.CreateInstance(
                    Type.GetType(Globals.Settings.Forums.ProviderType) );

        static ForumsProvider() { }

        static public ForumsProvider Instance
        {
            get
            {
                return _instance;
            }
        }

        public ForumsProvider()
        {
            this.ConnectionString = Globals.Settings.Forums.ConnectionString;
            this.EnableCaching = Globals.Settings.Forums.EnableCaching;
            this.CacheDuration = Globals.Settings.Forums.CacheDuration;
        }
        // other code below unchanged

certainly appears to follow the pattern from the article you quoted. any comments re the code above??

jimi

http://www.originaltalent.com

[trystanc]

Hi jimi,

That looks like it will do the trick.

The thing about thread safety is that 99.9% of the time the unsafe code will work fine as the chances of two threads colliding are very small.

Basically two page requests would have to come in at exactly the same time for the same resource (and be the first request for the resource since the app restarted so the instance variable is not set) for threads to collide. This is very unlikely, especially if the site doesn't have high traffic.

But the risk is always there...

[Maxxim]

I understand the risk, but choosing between grab the instance or creating a new instance everytime... it's hard

The jimi version minimize the risk but is it faster than the older one?

I think that processor burn more resources if he create a new activor.createinstance everytime the client call ForumsProvider Class, or not?

[jimibt]

max,

as it's defined as static, it'll only be initilised on the 1st invocation, so won't create a new resource each time. i wondered this too, so implemented the change debugged the code and found that it only get's created the 1st time around.

so my 'take' on this is that this new method is both 100% safer and doesn't suffer any decrease in efficiency or performance.

jimi

http://www.originaltalent.com

[Maxxim]

ummmm OK!

Then I guess i need to implement that! :)

[englere]

I've used code like this in some applications, got it from the same web page.

I only found one case where it couldn't work and I didn't take the time to figure out why. I just used code like Marco's with a lock verb in that case. That was a pretty deep architecture that was heavily interface driven. The code wasn't unreliable, it just plain didn't work in that case.

Eric