Thread safe macros?
If your referring to what I think you are, here's what I know:

1) The timing for a sequence of system macros, called from a keypad/controller macro, must be accounted for in the keypad/controller macro. If the first system macro has not completed before the second is called, the second one will be ignored (and possibly others that follow). Precise time delays are necessary.

2) The timing for a sequence of system macros, called from within another system macro, will automatically be accounted for by the processor. The processor won't start the second system macro until the first system macro is complete. No delays are necessary.

3) Multiple processors will run separate system macros simultaneously, when called from a single keypad/controller macro. No delays are necessary

Just my .02 cents.