在ASP.NET Core SignalR中管理DbContext生存期

Question

I have implemented an ASP.Core SignalR Application.

A shared hub class is invoking a signal to all its client on every 10 seconds from class SharedHub (this class is not inherited from Hub it has logic to get IHubContext to invoke)

public void Tick(){
    var time = _context.table.time;
    invoke('tick', time.tick);
}

Also in the same class once a new connection established a method called to update database

public void UpdateSocketConnection(int connectionId){
    var connection =_context.connection;
    connection.id = connectionId;
    _context.saveChanges();
}

Problem with this implementation is if the connection is currently calling Tick() method and also a client connected the same time. _context throws an error saying:

_context in use.

(I'll update exact error message once I reproduce).

What I have done ?

I have implemented a factory method to get a new instance of _context on top of every method

public void Tick(){
    var time = factory.GetContext().time;
    invoke('tick', time.tick);
}

public void UpdateSocketConnection(int connectionId){
    var context = Factory.getContext();

    var connection =context.connection;
    connection.id = connectionId;
    context .saveChanges();
}

This actually solved the problem. But it seems not the right thing to do. I am not sure of the performance when getting a new context every time on top of every method. this seems bad practice.

I want to know what are the possible implementation for this scenario.

Answer 1

In the first approach DbContext is shared between operations at the same time and it cause error and unexpected result. To avoid create and dispose DbContext every time in the second approach, DbContextPooling can help performance.

A pool of reusable instances can be created. Instead of disposing an instance, it returns to the pool and resets the instance to its default state. So instead of creating a new instance every time, the code will first check if there is an instance available in the pool or not.

You can enable DbContextPooling in Configure method in startup class:

services.AddDbContextPool<YourContext>(options => options.UseSqlServer(connection));

The default pool size value is 128. Read this article for more info.