[dmd-concurrency] draft 5

[Andrei Alexandrescu]

Sean Kelly wrote:
> void fnB() {
>     // do something that takes a while
> }
> void fnA() {
>     spawn( &fnB );
> }
> 
> void main() {
>     auto tid = spawn( &fnA );
>     tid.wait();
> }
> 
> The main thread doesn't know the thread running fnB exists so it can't wait for it, even if it's doing completely legitimate work and shouldn't be interrupted.  How can I trivially rewrite this program so it completes without error?

If fnB does legitimate work and doesn't call concurrency-related 
routines, it will be waited for.

If fnB does call concurrency-related routines, it must end when main() 
exits. To me exiting main() is a no-quarters situation: it means the 
application is to exit asap. I find it weird to think of programs that 
finish main() but continue to do stuff.

To make sure everything is accounted for, the application design must be 
such that main() doesn't exit until useful threads are done.


Andrei