bug#23875: 25.0.95; Emacs crashes when closing a frame on OSX

[Alan Third]

Ivan Cibrario Bertolotti <ivan.cibrario@polito.it> writes:

> Emacs occasionally crashes with a segmentation fault when deleting a
> frame on OSX.  The crash occurs with low probability, I am sorry I
> cannot provide a detailed recipe to reproduce it at the moment.

Can you provide any information about what you're doing when it crashes?
Are you just closing a frame with C-x 5 0?

> Looking at the crash report (at the bottom of this email) it seems to me
> that an EmacsImage is being deallocated by autorelease after it has
> already been freed, thus causing a NULL pointer dereference.
>
> Might this be another case of omitted bracketing with
> block_input()/unblock_input(), like in bug #23462?

It could be, but I don't think so. That one happened when the event
handler fired *within* the iconify function. I don't see anything in the
stack trace that looks like that.

> I am now running Emacs with NSTRACE_ENABLED.  If you have any better
> idea on how to gather more information, please let me know.  I am
> willing to help.

I'm not sure how to go about debugging this stuff, but NSZombiesEnabled
seems to be the way:

$ NSZombiesEnabled=YES /path/to/emacs.app/Contents/MacOS/Emacs

this should print out a message when an object is deallocated too many
times, instead of just crashing.
-- 
Alan Third