Originally Posted by R. Belmont
No, -mt wasn't fixed, at least by us. Please do not use it on OS X.

Okay, I thought this meant that multithreading was fixed on OS X. I've had it enabled since then and haven't had any issues.

http://mamedev.org/devwiki/index.php/MAME_0.143u2#Specific_Contributions

"Fix autorelease pool warnings when running multithreaded on Mac OS X [Tim Lindner]"