How to lock a shared object before serialization in Asp.net core SignalR?

Question

For example, if I have a static List<int> object that is manipulated by multi thread, it is not safe to enumerate it without locking it first. When I return the list from a hub method or send it to client, SignalR will internally serialize it without locking it.

In a asp.net core ApiController method I can fully custom serialize it first:

static List<int> list;
object Get()
{
    string s;
    lock(list)
    {
         s = JsonConvert.Serialize(list);
    }
    return new ContentResult(){ Content = s, ContentType = "application/json"};
}

It is not perfect but works.

I have some solutions on it:

1. Clone the object, before pass it to SignalR.

   Disadvantage: Clone is expensive. And deep clone needs more code.

2. Use Newtonsoft json's callback and error handling. For example:

//the shared object that will return from a hub method
class SomeObject
{
    public List<int> list;

    [OnSerializing]
    internal void OnSerializingMethod(StreamingContext context)
    {
        Monitor.Enter(this);
    }
    [OnSerialized]
    internal void OnSerializedMethod(StreamingContext context)
    {
        Monitor.Leave(this);
    }
    [OnError]
    internal void OnError(StreamingContext context, ErrorContext errorContext)
    {
        Monitor.Leave(this);
    }
}

But I'm not sure the OnSerializing/OnSerialized and OnSerializing/OnError will strictly be called by pair.

3. Is SyncRoot relate to or solve this problem?