Commits on Sep 9, 2023

1. Fix Vim crashing when querying serverlist when quitting …

   Currently, when quitting MacVim using Cmd-Q, if an autocmd queries
   serverlist() during shutdown (e.g.  VimLeavePre), there's a potential
   that Vim will crash and then stuck in a spinloop and never gets killed
   by the parent process.
   
   The reason is somehwat complicated. MMAppController tells Vim to quit
   but has a hard-coded timer before terminating the connection. If Vim
   takes too long to respond somehow, it will see a "connectionDidDie"
   message where it will be forced to quit. The serverlist() IPC API call
   isn't properly guarding against an invalid connection and if an autocmd
   triggers that call during this time, it will throw an exception and
   crash.
   
   Usually if Vim crashes, it should terminate cleanly, but couple things
   cause this to not work properly:
   - Vim's signal handler `deathtrap` tries to exit cleanly when a signal
     is detected, and it tries to call all deferred functions (added by
     :defer in Vimscript). The list of functions are allocated on the stack
     rather than the heap.
   - The ObjC exception is thrown inside a CFRunLoop (which is what called
     connectionDidDie) and CFRunLoop silently handles the exception before
     re-throwing it which triggers the actual abort signal to be caught by
     Vim's signal handler, but at this time, the deferred functions data
     structure is messed up as the stack is already gone since the first
     exception unwound it. This leads to a bogus memory state and lead to
     an infinite loop in `invoke_all_defer`.
   
   MacVim also doesn't have a solid mechanism to shut down zombie processes
   right now (it depends on Vim cleaning up after itself), so after MacVim
   quits, the now-orphaned Vim process stuck consuming 100% CPU.
   
   The fix is to simply guard against this and make sure we clean up the
   connection properly when we detected it died, and to be more defensive
   and make sure the serverlist call properly guard against invalid states
   and exceptions.
   
   Not tackling the other issues for now. There are some unfortunate
   interactions here with an unwound exception causing invoke_all_defer()
   to not work, but we just need to make sure to guard potential places
   with try/catch blocks, as invoke_all_defer() is still useful. Also,
   proper zombie process killing will be done at a later time, as we will
   soon tackle removing Distributed Objects/NSConnection and revamp the
   entire IPC stack anyway.
   
   Fix macvim-dev#1423

   

   ychin committed Sep 9, 2023
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