I’m writing a Mac bundle plugin, which runs its own thread (is that ok?). I need to have it signal back to Unity sometimes. If only to print a string to the console (‘print’ is not doing it for me). Is this possible?
You can not attach native code debuggers to managed code and unity runs managed or more precisely mixed code.
you can only attach the debugger to players built but even then, you can not set any breakpoints, again as its not native but mixed code. But at least you get a callstack when it crashes which might give you an idea.
To debug code running in unity, use monodevelop and attach the debugger to the unity process or the player process (you need to build the player as development - remote debugging enabled)