Welcome to OStack Knowledge Sharing Community for programmer and developer-Open, Learning and Share
Welcome To Ask or Share your Answers For Others

Categories

0 votes
617 views
in Technique[技术] by (71.8m points)

asp.net - Singleton Per Call Context (Web Request) in Unity

A few days ago, I had an issue with ASP.Net threading. I wanted to have a singleton object per web request. I actually need this for my unit of work. I wanted to instantiate a unit of work per web request so that identity map is valid through out the request. This way I could use an IoC to inject my own IUnitOfWork to my repository classes transparently, and I could use the same instance to query and then update my entities.

Since I am using Unity, I mistakenly used PerThreadLifeTimeManager. I soon realised that ASP.Net threading model does not support what I want to achieve. Basically it uses a threadpool and recycles threads, and that means that I get one UnitOfWork per thread!! However, what I wanted was one unit of work per web request.

A bit of googling gave me this great post. That was exactly what I wanted; except for the unity part which was quite easy to achieve.

This is my implementation for PerCallContextLifeTimeManager for unity:

public class PerCallContextLifeTimeManager : LifetimeManager
{
    private const string Key = "SingletonPerCallContext";

    public override object GetValue()
    {
        return CallContext.GetData(Key);
    }

    public override void SetValue(object newValue)
    {
        CallContext.SetData(Key, newValue);
    }

    public override void RemoveValue()
    {
    }
}

And of course I use this to register my unit of work with a code similar to this:

unityContainer
            .RegisterType<IUnitOfWork, MyDataContext>(
            new PerCallContextLifeTimeManager(),
            new InjectionConstructor());

Hope it saves someone a bit of time.

See Question&Answers more detail:os

与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…
Welcome To Ask or Share your Answers For Others

1 Answer

0 votes
by (71.8m points)

Neat solution, but each instance of LifetimeManager should use a unique key rather than a constant:

private string _key = string.Format("PerCallContextLifeTimeManager_{0}", Guid.NewGuid());

Otherwise if you have more than one object registered with PerCallContextLifeTimeManager, they're sharing the same key to access CallContext, and you won't get your expected object back.

Also worth implementing RemoveValue to ensure objects are cleaned up:

public override void RemoveValue()
{
     CallContext.FreeNamedDataSlot(_key);
}

与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…
Welcome to OStack Knowledge Sharing Community for programmer and developer-Open, Learning and Share
Click Here to Ask a Question

...