Expose methods on spawner in the API.

[DelSkayn]

Adds the poll_schedular and listen_spawn method.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 74.19355% with 16 lines in your changes are missing coverage. Please review.

Project coverage is 68.37%. Comparing base (304db5d) to head (1196234).

Files	Patch %	Lines
core/src/runtime/schedular.rs	56.66%	13 Missing ⚠️
core/src/context/ctx.rs	50.00%	3 Missing ⚠️

❗ Your organization needs to install the Codecov GitHub app to enable full functionality.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #313      +/-   ##
==========================================
+ Coverage   68.31%   68.37%   +0.06%     
==========================================
  Files          83       83              
  Lines       12237    12299      +62     
==========================================
+ Hits         8360     8410      +50     
- Misses       3877     3889      +12     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[DelSkayn]

Hmmm, I am still having some problems finding a good API here.

This PR has the problem that exposing poll and such introduces the ability to poll recursively: polling the scheduler from within a future currently being polled in the scheduler. The scheduler wasn't really designed with that in mind. I can add support for it but it is still hacky and I am not sure I want to expose this type of API.

[richarddd]

Hmmm, I am still having some problems finding a good API here.

This PR has the problem that exposing poll and such introduces the ability to poll recursively: polling the scheduler from within a future currently being polled in the scheduler. The scheduler wasn't really designed with that in mind. I can add support for it but it is still hacky and I am not sure I want to expose this type of API.

Thanks for the status update, I really appreciate the effort. Does this also mean that #312 is obsolete? All current blockers goes away if promises also drove spawned tasks forward.