Re: Multi-tasking
The only Mac Classic preemptive multi-tasking was running off various interrupts. The state of the entire system was always undefined at this time. You could only touch memory and devices that you had previous allocated and locked to a fixed hardware address. You could only call a handful of interrupt-level OS APIs, and most of those could only put your request into a queue for processing later. PowerPC was especially broken at the interrupt level because compiled code used CPU registers for program state.
All other backgrounding was cooperative. There was also a minimal cooperative Thread Manager that would do context swaps for you. You had to provide your own scheduler and communications mechanisms.
Yes, MacOS 7 was very nice to develop for but its API defined its own expiration. I ditched MacOS development when that mess of Objective-C was declared the official API. Swift's lame GC implementation didn't win me back either.
Biting the hand that feeds IT
