Should when_all[_with_variant] make any guarantees about completion context?

[ericniebler]

Issue by ericniebler
Wednesday Nov 17, 2021 at 17:49 GMT
Originally opened as NVIDIA/stdexec#262

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According to the current spec, when_all is permitted to complete any any arbitrary execution context. In practice though, it is guaranteed to complete in one of the contexts on which a child completes, or else it will complete inline in start. We could specify that or say nothing.

[lewissbaker]

The specification in P2300R10 of the default implementation of when_all is now detailed enough to infer that the completion context of the when_all() operation is either the context on which start() is called, or on one of the completion contexts of the child operations.

@ericniebler do we need anything more than this? e.g. do we need some specification to constrain where customisations are allowed to complete?