When will the garbage collector collect a Singleton?

Question

I have some SomeSingleton class in C# (.NET 3.5 if it matters) and code:

foo()
{
    ...
    SomeSingleton.Instance.DoSomething();
    ...
}

My question is: when will Garbage Collector collect this Singleton object?

p.s: code of SomeSingleton:

    private static SomeSingleton s_Instance = null;
    public static SomeSingleton Instance
    {
        get 
        {
            if (s_Instance == null)
            {
                lock (s_InstanceLock)
                {
                    if (s_Instance == null)
                    {
                        s_Instance = new SomeSingleton();
                    }
                }
            }
            return s_Instance;
        }
    }

Thanks for help!

EDIT (with explanation):

In Widnows Service I have code:

   ...
   FirstSingleton.Instance.DoSomething();
   ...

public class FirstSingleton
{
    (Instance part the same as in SomeSingleton)
    public void DoSomething()
    {
        SomeSingleton.Instance.DoSomething();
    }
}

What I want to achieve: I do not care what happens with FirstSingleton, but SomeSingleton starts Timer with first use of it, so I need SomeSingleton to exist (so the timer can run new thread every period of time) as long as my service is running.

As I understand from your answers all of that will happen because reference to my FirstSingleton and SomeSingleton is static, and singletons will not be collected by GC until service stops, am I right? :)

I believe its when the application terminates (along with the rest of the statics) (assuming the reference isn't removed) — Sayse, Aug 19 '13 at 12:40
It will never be garbage collected unless and until you set `s_Instance` to `null` and you don't have any other references of the same — Sriram Sakthivel, Aug 19 '13 at 12:43
As far as your code is concerned: Never. And this should not matter to you. When you worry about Dispose (!= collect) then ask about that. — H H, Aug 19 '13 at 12:46
this had been answered really perfectly at http://stackoverflow.com/a/538238/1856345 it contains everything you will need to know about GC and Idisposable interface, how to use both at managed and unmanaged resources edit: but answering your question , no GC doesn't deallocate static fields — Andrew, Aug 19 '13 at 12:48
This question isn't about `IDisposable`, it's about when static fields are eligible for collection. — Lee, Aug 19 '13 at 13:20
i know but it's all was explained there, you may simply ignore the IDisposable part and just focus on what you want there, but answering your question , no GC doesn't deallocate static fields — Andrew, Aug 19 '13 at 13:24
C# is based on Java, but I don't think a C# garbage collector question should be marked as a duplicate of a Java garbage collector question. — Denise Skidmore, Feb 13 '18 at 14:33

score 6 · Accepted Answer · edited May 23 '17 at 12:30

6

This question can be answered by this one: Do static members ever get garbage collected?

Basically, the instance will be destroyed when the containing AppDomain will get destroyed.

edited May 23 '17 at 12:30

Community

1
1

answered Aug 19 '13 at 12:41

Timotei

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score 1 · Answer 2 · edited May 23 '17 at 12:13

Objects referenced by static variables will only be garbage collected when the relevant AppDomain is garbage collected. In client applications, there's often just a single AppDomain which lives for the duration of the process. (An exception is when the application uses a plug-in architecture - different plug-ins may be loaded in different AppDomains and the AppDomain may be unloaded later.)

Refer

When will the garbage collector collect a Singleton?

2 Answers2