Hi Eli,

On 18/03/2025 02:21, Dmitry Gutov wrote:
> On 17/03/2025 21:41, Eli Zaretskii wrote:
>> Don't forget that
>> the target thread could be the main thread.
> 
> Good question what we should do with the main thread in this case - but 
> even if it receives the signal, it should be more a lot more visible to 
> the user than in background threads, helping fix whatever misbehavior 
> that caused it.
> 
> But we'll probably use the same method that's being discussed to declare 
> a thread an exception, prohibiting its buffer from being killed externally.

Here's a patch with implementation:

* It's a property of the thread, on by default.
* Set to nil for the main thread (currently can be changed from Lisp).
* Not a buffer-local variable - and looking more at it, that seems not a 
good idea, because several threads could have the same buffer current, 
and some might be okay with this behavior, while others not.
* A couple of questions about the finer details of the implementation, 
see comments in 'thread_all_before_buffer_killed'.
* Two tests included.

Seems to work well in my testing, and in the diff-hl scenario described 
in the report: step 5 kills the buffer and sends the signal which I can 
catch inside condition-case in diff-hl--update-safe.

WDYT?