C# Thread Static Variables

Question

I have a static DataLibrary class that implements a singleton pattern.

        public static FacilityRepository FacilRepo
        {
            get
            {
                if (_facilRepo == null)
                {
                    _facilRepo = new FacilityRepository(Authenticated.UserId);
                    if (Authenticated.FacKey.Length > 0)
                    {
                        foreach (var fac in _facilRepo)
                            fac.IsSelected = (fac.FacilityKey == Authenticated.FacKey);                        
                    }
                }
                return _facilRepo;
            }
        }

private static FacilityRepository _facilRepo;

When I access this from different threads using Task.Factory.StartNew the FacilityReposity gets recreated multiple times how can I avoid this.

If you are creating many new threads at the same time and they are all trying to access the FacilRepo property.. it may be because there is no locking around the property. Take a look at en.csharp-online.net/… (right at the bottom) — WiseGuyEh
– WiseGuyEh, Commented Mar 17, 2011 at 15:03

Jon Skeet · Accepted Answer · 2011-03-17 15:03:45Z

9

I don't think you've actually got a thread-local variable here - you've just got a race condition because you're not implementing the singleton pattern properly.

I have a page about the singleton pattern which gives some better options. (In particular, as you're using the TPL you must be using .NET 4, so the Lazy<T> option is definitely a contender.)

answered Mar 17, 2011 at 15:03

Jon Skeet

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1 Comment

Wegged Over a year ago

excellent Article!!!! Thank you . Ill accept your answer as soon as it lets me 4 more minutes.

Community · Accepted Answer · 2017-05-23 11:47:50Z

2

This Article by Jon Skeet might be helpful: Implementing the Singleton Pattern in C#

These questions might be helpful too:

edited May 23, 2017 at 11:47

CommunityBot

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answered Mar 17, 2011 at 15:07

gideon

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Comments

Artiom Chilaru · Accepted Answer · 2011-03-17 15:04:06Z

0

This would happen if multiple threads access your property for the first time, before _facilRepo is initialised. You have to lock the initialisation code like this:

private static object _facilRepoLock = new object();
public static FacilityRepository FacilRepo
{
    get
    {
        if (_facilRepo == null)
        {
            lock (_facilRepoLock)
            {
                if (_facilRepo == null)
                {
                    _facilRepo = new FacilityRepository(Authenticated.UserId);
                    if (Authenticated.FacKey.Length > 0)
                    {
                        foreach (var fac in _facilRepo)
                            fac.IsSelected = (fac.FacilityKey == Authenticated.FacKey);
                    }
                }
            }
        }
        return _facilRepo;
    }
}

private static FacilityRepository _facilRepo;

answered Mar 17, 2011 at 15:04

Artiom Chilaru

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2 Comments

Jon Skeet Over a year ago

Without the variable being volatile, I'm not sure that's genuinely thread-safe. There are simpler ways of achieving thread-safety than using double-checked locking.

Artiom Chilaru Over a year ago

Ahh, interesting.. I didn't know that before.. Your article is an eye-opener :)

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