C# Thread Static Variables

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

        public static FacilityRepository FacilR开发者_如何学Pythonepo
        {
            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.

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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.)

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

These questions might be helpful too:

• Singleton by Jon Skeet clarification
• Singleton Pattern with Public Constructor

---

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;