when_all polling implementation causes deadlock

[inbilla]

I'm experimenting with the implementation of when_all and it appears that the future that is created is always a 'polling' implementation? Is it possible to get a non-polling implementation (all the future's I've passed in are continuable)?
Additionally - the when_all_future doesn't appear continuable without using the free function then.

I had implemented a similar construct in my own library in the past, but it required modifying the future being waited upon to have a list of dependants. Potentially a similar construct could be added by adding a continuation to the future to check if the when_all_future is ready yet on the inline executor?

Because the when_all_future is polling, if I execute > num_cpus of when_all futures, then they can consume all the active threads and cause a deadlock in the executor.

To reproduce - I wait on a set of when_alls that are in turn waiting on futures that have been created by then.
That means that the when_all polling task is queued before the task represented by the thens are queued - causing it to wait forever and fail to make progress.

I know you're busy - So I appreciate you may not have time to assist
All the best