Subscriber is receiving 3 messages when publisher is only sending 1

[Roller007]

What I'm doing is pretty basic, I have a singleton messagehub, subscriber and publisher. When the publisher publishes the message only one message is being published. For some reason however the subscriber is receiving 3 messages. I have confirmed that this is what is happening through debugging. Any ideas?

[NimaAra]

I cannot help you without looking at your code. Please consider including a reproducible example which you can then zip up and attach to this issue for me to look at.

[jmdavid]

I do have the same problem. I send only once and receive 2.

[NimaAra]

Please provide a reproducible example for me to look at.

[jmdavid]

Thanks for answering.

Dotnet Core 2.1.101

in Startup.cs:

services.AddSingleton<ISandboxService, SandboxService>();
services.AddSingleton<IActWorkflowService, ActWorkflowService>();
services.AddSingleton<IActTaskService, ActTaskService>();

services.AddSingleton<IMessageHub, MessageHub>();

I have a service locator to inject singletons from Startup based on that article: https://dotnetcoretutorials.com/2018/05/06/servicelocator-shim-for-net-core/

In each service, I have:

private readonly IMessageHub hub;
private readonly Guid subscriptionToken;

And in the constructors of each service, I have this (just the name of the service is different in Console.WriteLine:

hub = MyServiceLocator.Current.GetInstance<IMessageHub>();
subscriptionToken = hub.Subscribe<ActHubMessage>(p => Console.WriteLine($"ActTaskService({subscriptionToken}): {p.messageType}"));

In SandboxService, I publish an object with a messageType property:

var msg1 = new ActHubMessage()
{
    messageType = ActHubMessage.HubMessageType.WorkflowTransition,
    workflowId = 1
};
hub.Publish(msg1);

Here is the output:

ActWorkflowService(bc467ca9-64c0-47e4-868d-fd1692bcbe03): TaskCancel
SandboxService(1e4ce11d-281a-4208-bd1c-886f5cd95f5b): TaskCancel
ActWorkflowService(e8c259d3-be2c-4cdc-8eb9-11fae38c7d7b): TaskCancel
ActTaskService(67e5bbdf-f83f-4752-aba5-7faaadaed9d1): TaskCancel
ActTaskService(73c1999f-e7c2-4f6c-998d-c01d504a946d): TaskCancel

Notice that SandboxService have only 1 token (it is the service that publish, the only one that both publish AND subscribe); in the other services, I have 2 tokens.

[jmdavid]

just in case:

namespace MyBackend
{
    //FROM THIS ARTICLE: https://dotnetcoretutorials.com/2018/05/06/servicelocator-shim-for-net-core/
    public class MyServiceLocator
    {
        private ServiceProvider _currentServiceProvider;
        private static ServiceProvider _serviceProvider;

        public MyServiceLocator(ServiceProvider currentServiceProvider)
        {
            _currentServiceProvider = currentServiceProvider;
        }

        public static MyServiceLocator Current
        {
            get
            {
                return new MyServiceLocator(_serviceProvider);
            }
        }

        public static void SetLocatorProvider(ServiceProvider serviceProvider)
        {
            _serviceProvider = serviceProvider;
        }

        public object GetInstance(Type serviceType)
        {
            return _currentServiceProvider.GetService(serviceType);
        }

        public TService GetInstance<TService>()
        {
            return _currentServiceProvider.GetService<TService>();
        }
    }
}

[NimaAra]

Please put all of that into a project where I can clone or even zip it up.

[jmdavid]

The problem seems to be the mix of DI.

In 2.1, it was not possible to inject in service like we do in controllers.

This works:

public SandboxController(ISandboxService _sandboxService, IActTaskService _actTaskService...

This NOT works:

public SandboxService(IActTaskService _taskService...

That's why I used the ServiceLocator to inject services in other services like this:

actTaskService = MyServiceLocator.Current.GetInstance<IActTaskService>();

However, I still use the first pattern in my controllers. And I realized that I inject ActTaskService and ActWorkflowService in 2 controllers, in correponding controller (ActTaskController, ActWorfklowController) AND in SandboxController (that I use as a scratchpad). As long as I removed the 2 services from SandboxController, the class is instantiated only once.

But I wonder why injection in controllers creates a new instance.