ArgumentException when adding large number of subscriptions

[sidhoda]

The following code will more often than not result in an ArgumentException being raised with the message "An item with the same key has already been added.":

var bus = BusSetup.StartWith<AsyncConfiguration>().Construct();

for (uint i = 0; i < 100000; i++)
{
    bus.Subscribe((int x) => Console.WriteLine(x));
}

Relevant part of the exception stack trace is

   at System.ThrowHelper.ThrowArgumentException(ExceptionResource resource)
   at System.Collections.Generic.Dictionary`2.Insert(TKey key, TValue value, Boolean add)
   at MemBus.CompositeSubscription.JustAdd(ISubscription subscription)
   at MemBus.CompositeSubscription.Add(ISubscription subscription)
   at MemBus.CompositeResolver.Add(ISubscription subscription)
   at MemBus.Subscriber.Subscribe[M](Action`1 subscription, ISubscriptionShaper customization)
   at MemBus.Subscriber.Subscribe[M](Action`1 subscription)
   at MemBus.MessageObservable`1.Subscribe(IObserver`1 observer)
   at System.ObservableExtensions.SubscribeSafe[T](IObservable`1 source, IObserver`1 observer)

My guess is that two DisposableSubscription instances have the same hashcode, resulting in a collision when attempting to add it the subscription storage:

MemBus/MemBus/CompositeSubscription.cs

Line 99 in 8613a7e

_subscriptions.Add(disposableSub.GetHashCode(), disposableSub);

Changing the subscriptions storage to HashSet would be a possible fix as the default IEqualityComparer will check for equality (in this case reference equality) when getting multiple elements with the same hash code.

[jkonecki]

I'm getting the same exception with much lower number of subscriptions: ~20

[flq]

Hey, thanks for the PR, wondering why this was a Dictionary right now. Pre-Hashset-time?

How could you verify that this sorts you out?

I wanted to push a new version with netstandard as target, but I need to migrate the project.json stuff I have also.

[jkonecki]

I've added a unit test that @sidhoda suggested.
I cannot get the Test project to compile on my machine due to project.json references issue. I hope it will work on yours.
I've updated my project and haven't noticed the exception anymore.

[flq]

Sorry that your PR is sitting there, but I tried to upgrade to the new csproj stuff from .NET Core and looks like I failed, so I am doing another version with the project.json stuff and then hopefully I have the stuff up and running again.

[flq]

This has been fixed with commit e28770a.