Refactor cancellation mechanism and make it internal, accessible via experimental nuget.

[codemzs]

fixes #2795

[glebuk]

public interface IHostEnvironment : IChannelProvider, IProgressChannelProvider

Seems like there are potential scenarios where this feature might be critical, perhaps lets first evaluate various options on enable it short term and have a stable design for the long term #Closed

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Refers to: src/Microsoft.ML.Core/Data/IHostEnvironment.cs:57 in 48be42f. [](commit_id = 48be42f, deletion_comment = False)

[eerhardt]

We should add some unit tests for this capability. #Resolved

[codemzs]

There is a unit-test that checks for cancel signal but I think what you are referring to is testing cancellation on a pipeline. For that to happen we will need to implement checks in our components for this cancellation signal and cancel the pipeline but this is not within the scope of this PR.

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In reply to: 472159903 [](ancestors = 472159903)

[eerhardt]

You are adding a new public API -

public static class Experimental
    {
        /// <summary>
        /// Stop the exeuction of pipeline in <see cref="MLContext"/>
        /// </summary>
        /// <param name="ctx"></param>
        public static void StopExecution(this MLContext ctx) => ctx.StopExecution();

Adding unit tests for that new public API is within the scope of this PR. #Resolved

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@0831865). Click here to learn what that means.
The diff coverage is 100%.

@@            Coverage Diff            @@
##             master    #2797   +/-   ##
=========================================
  Coverage          ?   72.34%           
=========================================
  Files             ?      803           
  Lines             ?   143445           
  Branches          ?    16171           
=========================================
  Hits              ?   103778           
  Misses            ?    35247           
  Partials          ?     4420

Flag	Coverage Δ
#Debug	72.34% <100%> (?)
#production	68.05% <100%> (?)
#test	88.53% <100%> (?)

Impacted Files	Coverage Δ
src/Microsoft.ML.Core/Data/IHostEnvironment.cs	95.12% <ø> (ø)
...est/Microsoft.ML.Core.Tests/UnitTests/TestHosts.cs	100% <100%> (ø)
src/Microsoft.ML.Data/MLContext.cs	94.73% <100%> (ø)
...rc/Microsoft.ML.Data/Utilities/LocalEnvironment.cs	85.96% <100%> (ø)

[codemzs]

Done.

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In reply to: 472161675 [](ancestors = 472161675)

[eerhardt]

Just some minor nits to clean up. Other than that, this approach looks fine.