Fixed unhandled exception when plotting a live event histogram

[GuiMacielPereira]

Description of work

Fixed unhandled exception found in manual testing, as detailed in #36726

Summary of work

Caught RunTime error exception and replaced it by logging an error to the console.

Avoids an uncaught exception. This behaviour was already present in previous versions of mantid.

Fixes #36726 .

Further detail of work

This error only happens at a high updating fequency. When we select the live data interface to update every 1 second, the workspace in the ADS gets rewritten every 1 second. When the plotting is still loading the data will change, which causes a RunTime error: Variable invalidated, data has been deleted.. If you select this update to 5 seconds, the plot will usually happen with no issues.

To test:

Here is a summary:

1. Change facility and test instrument to TEST_LIVE and ISIS_HISTOGRAM
2. Execute FakeISISEventDAE (use defaults)
3. Execute FakeISISHistoDAE (use defaults)
4. Click Load > Live Data
5. Set parameters:
   Instrument: ISIS_Histogram
   Connection: Histo
   Starting time: Now
   Update every: 1 second
   No processing
   Accumulation method: Replace
   No processing
   Output workspace: live_histo_ws
6. Click run
7. Double click on workspace that shows up on ADS and plot all spectra

An error should be logged saying that data has been deleted.

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[GuiMacielPereira]

Here I opted to only cover the plot_fom_names function inside the try block.

• Should the try block be bigger?

Then I have an if/else statement to check that the RunTime error caught is specifically the one relating to the deleted data.

• Should I use a regular expression in this if statement instead?
• If in the future the message for this runtime error changes, then the if statement will always yield false, is there any way to prevent this?

[GuiMacielPereira]

Here I opted to only cover the plot_fom_names function inside the try block.

• Should the try block be bigger?

Then I have an if/else statement to check that the RunTime error caught is specifically the one relating to the deleted data.

• Should I use a regular expression in this if statement instead?
• If in the future the message for this runtime error changes, then the if statement will always yield false, is there any way to prevent this?

[thomashampson]

This is also happening in 6.8, so do we need to put it in for the release?

[GuiMacielPereira]

You're correct, for some reason I thought I had tried it in 6.8 and that it was a regression, but I just tried it again and it does indeed give the same unhandled exception. I also tried it on an older version of mantid and it was there as far back as 6.5.

This is not a regression, so it does not have to go into release. I'll take it back from the release board.