Make sure promise polls spawner

[richarddd]

Promise converted into a future will now advance spawned tasks

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.33%. Comparing base (304db5d) to head (cc1dfce).

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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #312      +/-   ##
==========================================
+ Coverage   68.31%   68.33%   +0.01%     
==========================================
  Files          83       83              
  Lines       12237    12243       +6     
==========================================
+ Hits         8360     8366       +6     
  Misses       3877     3877              

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[richarddd]

@DelSkayn can we merge this if put behind a feature flag?

[richarddd]

@DelSkayn this is now gated behind promise_poll_spawner. Would that be OK?

[DelSkayn]

There is currently still an issue on this PR. It is possible for a task to become unblocked while it is polling, which would allow it to poll itself, finish and then free it's own task.

[richarddd]

There is currently still an issue on this PR. It is possible for a task to become unblocked while it is polling, which would allow it to poll itself, finish and then free it's own task.

Can we track this somehow? Or add primitives to prevent this?