Fix crash due to subscribing observer twice to notification center

[robertapplin]

Report to: Franz Demmel

Description of work

This PR fixes a consistent crash when using multiple of the Indirect and Inelastic interfaces. It is possible to cause this crash in multiple different ways, from multiple different interfaces. It is caused by adding the same observer to the notification center more than once, and the solution was easy - not to add the observer if it is already subscribed to the notification center.

Fixes #37071

To test:

1. Go to 'Inelastic'->Data Manipulations
2. Load data into the Symmetrise Tab
3. Click Preview, then click Run
4. Close the interface
5. Open the Data Analysis interface
6. On MSD Fit load data
7. Select Gaus function
8. Click Run. There should be no crash

Reviewer

Please comment on the points listed below (full description).
Your comments will be used as part of the gatekeeper process, so please comment clearly on what you have checked during your review. If changes are made to the PR during the review process then your final comment will be the most important for gatekeepers. In this comment you should make it clear why any earlier review is still valid, or confirm that all requested changes have been addressed.

Code Review

• Is the code of an acceptable quality?
• Does the code conform to the coding standards?
• Are the unit tests small and test the class in isolation?
• If there is GUI work does it follow the GUI standards?
• If there are changes in the release notes then do they describe the changes appropriately?
• Do the release notes conform to the release notes guide?

Functional Tests

• Do changes function as described? Add comments below that describe the tests performed?
• Do the changes handle unexpected situations, e.g. bad input?
• Has the relevant (user and developer) documentation been added/updated?

Does everything look good? Mark the review as Approve. A member of @mantidproject/gatekeepers will take care of it.

Gatekeeper

If you need to request changes to a PR then please add a comment and set the review status to "Request changes". This will stop the PR from showing up in the list for other gatekeepers.

[adriazalvarez]

Tested and it fixes the crash. Hopefully making using interfaces more stable. Happy to approve this.

As a general question, do you know why is there any limitation to the number of observers that can be subscribed to the ads?

[robertapplin]

Tested and it fixes the crash. Hopefully making using interfaces more stable. Happy to approve this.

As a general question, do you know why is there any limitation to the number of observers that can be subscribed to the ads?

Any number of observers can be subscribed. Its more that the same observer should not be subscribed twice to the notification center. When you close an interface, you tend to remove the observer from the notification center. This will only remove the first instance of the subscription, so if your observer is subscribed twice, then your observer is still subscribed

[jhaigh0]

Maybe in future we can look at adding a check within addObserver itself that calls hasObserver to avoid duplicates being added entirely.

[robertapplin]

Maybe in future we can look at adding a check within addObserver itself that calls hasObserver to avoid duplicates being added entirely.

The addObserver method is part of the Poco library, so we would have to create a wrapper around addObserver somehow

[robertapplin]

It might be better to get PreviewPlot to inherit from AnalysisDataServiceObserver in the future

mantid/Framework/API/inc/MantidAPI/AnalysisDataServiceObserver.h

Line 38 in b596a22

class MANTID_API_DLL AnalysisDataServiceObserver {

[robertapplin]

@mantidproject/gatekeepers Please can we merge this before end of today? 🙂