🚧Prevent unsubscription in OnRecieve

[CalvinWilkinson]

Complete The Item Below

• I have updated the title without removing the 🚧 emoji.

Description

Prevent an unsubscriber object from unusubscribing when its Dispose() method is called in an OnReceieve() call.

This can be prevented by invoking an exception. This is because if a user unsubscribes inside of an OnReceieve() method call, this can cause issues due to processing each subscription at a time in the reactables.

To prevent this from being an issue, the for loops in the reactables all iterate the list of subscriptions from the end of the loop to the beginning so it does not try to access a subscription item that does not exist.

Why is this?
When a SubscriptionUnsubscriber.Dispose()' method is called, it directly removes the subscription from the reactable's underlying array. The OnReceieve()` methods are invoked in an array. This can cause a state of accessing an item that has been removed.

If we throw an exception from the unsubscriber, this will prevent users from trying to call the Dispose() method in the OnReceieve() call stack.

How to prevent this?
Internally, have the reactable communicate a state that the reactable is in the middle of processing notifications. If this is the case, the Dispose() method of the unsubscriber should throw an exception.

1. Add a new parameter with the type Func<bool> and the name isProcessing to the SubscriptionUnsubscriber constructor. The bool value will be the processing state that the reactable is currently in. A value of true will mean that notifications are being processed and false means it is not.

Note

The ReactableBase class will have a private method that returns a bool value that will be passed as the new ctor
parameter of the `SubscriptionUnsubsciber' class. The unsubscriber will then invoke this to check the processing
state of the reactable that the subscription belongs to.

2. In the methods Push and SendError methods of the PushReactable<TIn> and NonDirectional.PushReactable classes, set the state to processing before the loops start and to not processing after the loops end.
3. Do the same thing for the PushPullReactable<TIn, TOut>.PushPull method.

Before the loop starts in the reactables, set the value of this property for each subscription

Acceptance Criteria

The items to complete in order to satisfy the Definition of Done.

Beta Give feedback

1. The SubscriptionUnsubscriber ctor has a new param of type Func<bool>
2. The name of the new ctor param is isProcessing
3. The loops in the NonDirectional.PushReactable class updated to set internal processing state
4. The loops in the OneWay.PushReactable class updated to set internal processing state
5. The loops in the PushReactable<TIn> class updated to set the internal processing state
6. The loops in the PushPullReactable<TIn, TOut> class updated to set the internal processing state
7. The Dispose() method in the SubscriptionUnsubscriber class throws an exception if the reactables are currently processing

ToDo Items

The items to complete in order to satisfy the Definition of Done.

Beta Give feedback

1. Change type labels added to this issue. Refer to the Change Type Labels section below.
2. Priority label added to this issue. Refer to the Priority Type Labels section below.
3. Issue linked to the correct milestone (if applicable).

Issue Dependencies

No response

Related Work

No response

Additional Information:

Change Type Labels

Change Type	Label
Bug Fixes	🐛bug
Breaking Changes	🧨breaking changes
New Feature	✨new feature
CICD Changes	♻️cicd
Config Changes	⚙️config
Performance Improvements	🏎️performance
Code Doc Changes	🗒️documentation/code
Product Doc Changes	📝documentation/product

Priority Type Labels

Priority Type	Label
Low Priority	low priority
Medium Priority	medium priority
High Priority	high priority

Code of Conduct

• I agree to follow this project's Code of Conduct.