29.0.50 master freeze on macOS

[Alexander Adolf]

Hello,

I get a complete lockup of Emacs a couple of times a day on macOS. I
built Emacs from commit e4030f25f98d2ac9c638e573b0ab6e6b0a35f38b
yesterday, but the freeze started occurring a while back with one of the
28 versions. I don't recall exactly when.

When the freeze happens, Emacs is completely frozen, that is,
emacsclients are locked up too, and neither SIGUSR1 nor SIGUSR2 change
anything. The only way forward is killing the process, an restarting it.

I'm running the nextstep build (i.e. Emacs.app), and macOS generates a
crash report when a GUI app hangs. In that report, four threads are
shown:

- com.apple.main-thread: the trace doesn't reveal much as the call trace
  leads into the OS kernel, where symbol names are rare. It seems there
  is some sort of interrupt going on, followed by a memmove().

- gmain: the trace for this thread goes from a thread_start relatively
  straight to end in a select().

- an unnamed thread: the trace for this thread goes from a thread_start
  relatively straight to end in a pselect().

- com.apple.NSEventThread: the trace for this thread goes from a
  thread_start relatively straight into a CFRunLoopServiceMachPort(),
  and ends a ipc_mqueue_receive_continue().


Any hints how I could go about further narrowing in on the problem, i.e.
building with debug symbols, etc.?

Any hints appreciated.

  --alexander