With the recent upgrade to macOS 10.12.4 and Xcode 8.3, we're seeing a SIGSEGV/EXC_BAD_ACCESS with pthread_mutex_lock() which is part of the initialization of the ACE libraries. I haven't done enough debugging to know whether it's caused by an incompatibility between ACE and the 10.12.4 runtimes (e.g., a struct has changed in size) or if it's an actual bug in the runtimes. Mike Martell found a bug that has already been filed about Emacs crashing with pthread-related problems after this update, so our current theory is that there's a problem in the pthreads library from Apple.
Sarge
