jgorbe added inline comments.

================
Comment at: lldb/source/DataFormatters/FormatManager.cpp:595
+  {
+    std::lock_guard<std::recursive_mutex> guard(m_language_categories_mutex);
+    m_language_categories_map[lang_type] =
----------------
hawkinsw wrote:
> Forgive me if I am speaking out of turn, but do we need to check again here 
> for whether `lang_type` is in the map? In other words, it seems possible that 
> (in some zany situation) while we are doing the memory allocation (line 593) 
> someone else has come along and added that category since we released the 
> lock on it in 592. 
> 
> I hope that this is helpful. Please (again) forgive me if I am speaking out 
> of turn.
Not at all! Thank you for your comment! :)

You are absolutely right, I had overlooked this case. Another annoying 
consequence is that in this case the racing threads would create multiple 
`LanguageCategory` objects. The `LanguageCategory` constructor calls `Enable` 
which in turn ends up calling the `Changed` method of the listener, so even if 
we check the map before insertion I think we'd still see the listener receiving 
multiple notifications that the category was enabled, which is not ideal.

I don't know how to properly fix this. I'll give it some more thought.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D126240/new/

https://reviews.llvm.org/D126240

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