[Pitch] Custom Main and Global Executors

[ktoso (Konrad 'ktoso' Malawski 🐟🏴‍☠️)]

@Joe_Groff

The places where the main actor is implicit are fairly rare IIRC, so in most cases code can explicitly use a different global actor instead of replacing the one MainActor.

That used to be kind of true, except ongoing proposals are aiming to enable "everything in this module is on the main actor" by default (on a module by module basis) ([Pitch] Control default actor isolation inference) which does make code implicitly on the main actor be pretty ubiquitous. So it seems to be that more than not-special, it is going to become more special than currently.

@Joe_Groff

The tradeoff with hooking it globally is that only one person gets to do that, so as your application grows and needs to ingest preexisting pieces that use raw Win32, MFC, and Qt, relying on one true MainActor implementation seems like it could be a scaling liability when components with different expectations written against different implementations collide.

That's true that one person gets to set it, but also it's "wherever the app/system" runs -- and that's going to be one of those platforms / runtimes, and very rarely there's multiple "assumption of main thread" that are conflicting but active at the same time...? Usually those frameworks take full ownership of the programming model, don't they?