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

Microsoft.ML.sln

@@ -266,6 +266,8 @@ Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Microsoft.ML.Ensemble", "Mi
 		pkg\Microsoft.ML.Ensemble\Microsoft.ML.Ensemble.symbols.nupkgproj = pkg\Microsoft.ML.Ensemble\Microsoft.ML.Ensemble.symbols.nupkgproj
 	EndProjectSection
 EndProject
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Microsoft.ML.Experimental", "src\Microsoft.ML.Experimental\Microsoft.ML.Experimental.csproj", "{E02DA82D-3FEE-4C60-BD80-9EC3C3448DFC}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -948,6 +950,18 @@ Global
 		{5E920CAC-5A28-42FB-936E-49C472130953}.Release-Intrinsics|Any CPU.Build.0 = Release-Intrinsics|Any CPU
 		{5E920CAC-5A28-42FB-936E-49C472130953}.Release-netfx|Any CPU.ActiveCfg = Release-netfx|Any CPU
 		{5E920CAC-5A28-42FB-936E-49C472130953}.Release-netfx|Any CPU.Build.0 = Release-netfx|Any CPU
+		{E02DA82D-3FEE-4C60-BD80-9EC3C3448DFC}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{E02DA82D-3FEE-4C60-BD80-9EC3C3448DFC}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{E02DA82D-3FEE-4C60-BD80-9EC3C3448DFC}.Debug-Intrinsics|Any CPU.ActiveCfg = Debug-Intrinsics|Any CPU
+		{E02DA82D-3FEE-4C60-BD80-9EC3C3448DFC}.Debug-Intrinsics|Any CPU.Build.0 = Debug-Intrinsics|Any CPU
+		{E02DA82D-3FEE-4C60-BD80-9EC3C3448DFC}.Debug-netfx|Any CPU.ActiveCfg = Debug-netfx|Any CPU
+		{E02DA82D-3FEE-4C60-BD80-9EC3C3448DFC}.Debug-netfx|Any CPU.Build.0 = Debug-netfx|Any CPU
+		{E02DA82D-3FEE-4C60-BD80-9EC3C3448DFC}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{E02DA82D-3FEE-4C60-BD80-9EC3C3448DFC}.Release|Any CPU.Build.0 = Release|Any CPU
+		{E02DA82D-3FEE-4C60-BD80-9EC3C3448DFC}.Release-Intrinsics|Any CPU.ActiveCfg = Release-Intrinsics|Any CPU
+		{E02DA82D-3FEE-4C60-BD80-9EC3C3448DFC}.Release-Intrinsics|Any CPU.Build.0 = Release-Intrinsics|Any CPU
+		{E02DA82D-3FEE-4C60-BD80-9EC3C3448DFC}.Release-netfx|Any CPU.ActiveCfg = Release-netfx|Any CPU
+		{E02DA82D-3FEE-4C60-BD80-9EC3C3448DFC}.Release-netfx|Any CPU.Build.0 = Release-netfx|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
@@ -1033,6 +1047,7 @@ Global
 		{31D38B21-102B-41C0-9E0A-2FE0BF68D123} = {D3D38B03-B557-484D-8348-8BADEE4DF592}
 		{5E920CAC-5A28-42FB-936E-49C472130953} = {AED9C836-31E3-4F3F-8ABC-929555D3F3C4}
 		{AD7058C9-5608-49A8-BE23-58C33A74EE91} = {D3D38B03-B557-484D-8348-8BADEE4DF592}
+		{E02DA82D-3FEE-4C60-BD80-9EC3C3448DFC} = {09EADF06-BE25-4228-AB53-95AE3E15B530}
 	EndGlobalSection
 	GlobalSection(ExtensibilityGlobals) = postSolution
 		SolutionGuid = {41165AF1-35BB-4832-A189-73060F82B01D}

pkg/Microsoft.ML.Experimental/Microsoft.ML.Experimental.nupkgproj

@@ -0,0 +1,12 @@
+<Project Sdk="Microsoft.NET.Sdk" DefaultTargets="Pack">
+
+  <PropertyGroup>
+    <TargetFramework>netstandard2.0</TargetFramework>
+    <PackageDescription>Microsoft.ML.Experimental contains experimental work such extension methods to access internal methods.</PackageDescription>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="../Microsoft.ML/Microsoft.ML.nupkgproj" />
+  </ItemGroup>
+
+</Project>

pkg/Microsoft.ML.Experimental/Microsoft.ML.Experimental.symbols.nupkgproj

@@ -0,0 +1,5 @@
+<Project DefaultTargets="Pack">
+
+  <Import Project="Microsoft.ML.Experimental.nupkgproj" />
+
+</Project>

src/Microsoft.ML.Core/Data/IHostEnvironment.cs

@@ -63,14 +63,23 @@ public interface IHostEnvironment : IChannelProvider, IProgressChannelProvider
         IHost Register(string name, int? seed = null, bool? verbose = null);
 
         /// <summary>
-        /// Flag which indicate should we stop any code execution in this host.
+        /// The catalog of loadable components (<see cref="LoadableClassAttribute"/>) that are available in this host.
         /// </summary>
-        bool IsCancelled { get; }
+        ComponentCatalog ComponentCatalog { get; }
+    }
 
+    [BestFriend]
+    internal interface ICancelable
+    {
         /// <summary>
-        /// The catalog of loadable components (<see cref="LoadableClassAttribute"/>) that are available in this host.
+        /// Signal to stop exection in all the hosts.
         /// </summary>
-        ComponentCatalog ComponentCatalog { get; }
+        void CancelExecution();
+
+        /// <summary>
+        /// Flag which indicates host execution has been stopped.
+        /// </summary>
+        bool IsCanceled { get; }
     }
 
     /// <summary>
@@ -85,11 +94,6 @@ public interface IHost : IHostEnvironment
         /// generators are NOT thread safe.
         /// </summary>
         Random Rand { get; }
-
-        /// <summary>
-        /// Signal to stop exection in this host and all its children.
-        /// </summary>
-        void StopExecution();
     }
 
     /// <summary>

src/Microsoft.ML.Core/Environment/ConsoleEnvironment.cs

@@ -465,7 +465,7 @@ private sealed class Host : HostBase
             public Host(HostEnvironmentBase<ConsoleEnvironment> source, string shortName, string parentFullName, Random rand, bool verbose)
                 : base(source, shortName, parentFullName, rand, verbose)
             {
-                IsCancelled = source.IsCancelled;
+                IsCanceled = source.IsCanceled;
             }
 
             protected override IChannel CreateCommChannel(ChannelProviderBase parent, string name)

src/Microsoft.ML.Core/Environment/HostEnvironmentBase.cs

@@ -93,9 +93,23 @@ internal interface IMessageSource
     /// query progress.
     /// </summary>
     [BestFriend]
-    internal abstract class HostEnvironmentBase<TEnv> : ChannelProviderBase, IHostEnvironment, IChannelProvider
+    internal abstract class HostEnvironmentBase<TEnv> : ChannelProviderBase, IHostEnvironment, IChannelProvider, ICancelable
         where TEnv : HostEnvironmentBase<TEnv>
     {
+        void ICancelable.CancelExecution()
+        {
+            lock (_cancelLock)
+            {
+                foreach (var child in _children)
+                    if (child.TryGetTarget(out IHost host))
+                        if (host is ICancelable cancelableHost)
+                            cancelableHost.CancelExecution();
+
+                _children.Clear();
+                IsCanceled = true;
+            }
+        }
+
         /// <summary>
         /// Base class for hosts. Classes derived from  <see cref="HostEnvironmentBase{THostEnvironmentBase}"/> may choose
         /// to provide their own host class that derives from this class.
@@ -107,28 +121,10 @@ public abstract class HostBase : HostEnvironmentBase<TEnv>, IHost
 
             public Random Rand => _rand;
 
-            // We don't have dispose mechanism for hosts, so to let GC collect children hosts we make them WeakReference.
-            private readonly List<WeakReference<IHost>> _children;
-
             public HostBase(HostEnvironmentBase<TEnv> source, string shortName, string parentFullName, Random rand, bool verbose)
                 : base(source, rand, verbose, shortName, parentFullName)
             {
                 Depth = source.Depth + 1;
-                _children = new List<WeakReference<IHost>>();
-            }
-
-            public void StopExecution()
-            {
-                lock (_cancelLock)
-                {
-                    IsCancelled = true;
-                    foreach (var child in _children)
-                    {
-                        if (child.TryGetTarget(out IHost host))
-                            host.StopExecution();
-                    }
-                    _children.Clear();
-                }
             }
 
             public new IHost Register(string name, int? seed = null, bool? verbose = null)
@@ -139,7 +135,7 @@ public void StopExecution()
                 {
                     Random rand = (seed.HasValue) ? RandomUtils.Create(seed.Value) : RandomUtils.Create(_rand);
                     host = RegisterCore(this, name, Master?.FullName, rand, verbose ?? Verbose);
-                    if (!IsCancelled)
+                    if (!IsCanceled)
                         _children.Add(new WeakReference<IHost>(host));
                 }
                 return host;
@@ -175,7 +171,7 @@ protected PipeBase(ChannelProviderBase parent, string shortName,
 
             public void Dispose()
             {
-                if(!_disposed)
+                if (!_disposed)
                 {
                     Dispose(true);
                     _disposed = true;
@@ -339,12 +335,15 @@ public void RemoveListener(Action<IMessageSource, TMessage> listenerFunc)
 
         protected readonly ProgressReporting.ProgressTracker ProgressTracker;
 
-        public bool IsCancelled { get; protected set; }
-
         public ComponentCatalog ComponentCatalog { get; }
 
         public override int Depth => 0;
 
+        public bool IsCanceled { get; protected set; }
+
+        // We don't have dispose mechanism for hosts, so to let GC collect children hosts we make them WeakReference.
+        private readonly List<WeakReference<IHost>> _children;
+
         /// <summary>
         ///  The main constructor.
         /// </summary>
@@ -359,6 +358,7 @@ protected HostEnvironmentBase(Random rand, bool verbose,
             _cancelLock = new object();
             Root = this as TEnv;
             ComponentCatalog = new ComponentCatalog();
+            _children = new List<WeakReference<IHost>>();
         }
 
         /// <summary>
@@ -379,13 +379,20 @@ protected HostEnvironmentBase(HostEnvironmentBase<TEnv> source, Random rand, boo
             ListenerDict = source.ListenerDict;
             ProgressTracker = source.ProgressTracker;
             ComponentCatalog = source.ComponentCatalog;
+            _children = new List<WeakReference<IHost>>();
         }
 
         public IHost Register(string name, int? seed = null, bool? verbose = null)
         {
             Contracts.CheckNonEmpty(name, nameof(name));
-            Random rand = (seed.HasValue) ? RandomUtils.Create(seed.Value) : RandomUtils.Create(_rand);
-            return RegisterCore(this, name, Master?.FullName, rand, verbose ?? Verbose);
+            IHost host;
+            lock (_cancelLock)
+            {
+                Random rand = (seed.HasValue) ? RandomUtils.Create(seed.Value) : RandomUtils.Create(_rand);
+                host = RegisterCore(this, name, Master?.FullName, rand, verbose ?? Verbose);
+                _children.Add(new WeakReference<IHost>(host));
+            }
+            return host;
         }
 
         protected abstract IHost RegisterCore(HostEnvironmentBase<TEnv> source, string shortName,

src/Microsoft.ML.Core/Utilities/Contracts.cs

@@ -737,6 +737,7 @@ public static void CheckIO(this IExceptionContext ctx, bool f, string msg)
             if (!f)
                 throw ExceptIO(ctx, msg);
         }
+
         public static void CheckIO(this IExceptionContext ctx, bool f, string msg, params object[] args)
         {
             if (!f)
@@ -748,11 +749,10 @@ public static void CheckIO(this IExceptionContext ctx, bool f, string msg, param
         /// </summary>
         public static void CheckAlive(this IHostEnvironment env)
         {
-            if (env.IsCancelled)
+            if (env is ICancelable cancelableEnv && cancelableEnv.IsCanceled)
                 throw Process(new OperationCanceledException("Operation was cancelled."), env);
         }
 #endif
-
         /// <summary>
         /// This documents that the parameter can legally be null.
         /// </summary>

src/Microsoft.ML.Data/MLContext.cs

@@ -3,6 +3,7 @@
 // See the LICENSE file in the project root for more information.
 
 using System;
+using System.Collections.Generic;
 using Microsoft.ML.Data;
 using Microsoft.ML.Runtime;
 
@@ -104,12 +105,14 @@ private void ProcessMessage(IMessageSource source, ChannelMessage message)
             log(this, new LoggingEventArgs(msg));
         }
 
-        bool IHostEnvironment.IsCancelled => _env.IsCancelled;
         string IExceptionContext.ContextDescription => _env.ContextDescription;
         TException IExceptionContext.Process<TException>(TException ex) => _env.Process(ex);
         IHost IHostEnvironment.Register(string name, int? seed, bool? verbose) => _env.Register(name, seed, verbose);
         IChannel IChannelProvider.Start(string name) => _env.Start(name);
         IPipe<TMessage> IChannelProvider.StartPipe<TMessage>(string name) => _env.StartPipe<TMessage>(name);
         IProgressChannel IProgressChannelProvider.StartProgressChannel(string name) => _env.StartProgressChannel(name);
+
+        [BestFriend]
+        internal void CancelExecution() => ((ICancelable)_env).CancelExecution();
     }
 }

src/Microsoft.ML.Data/Properties/AssemblyInfo.cs

@@ -45,6 +45,7 @@
 [assembly: InternalsVisibleTo(assemblyName: "Microsoft.ML.DnnImageFeaturizer.ResNet50" + PublicKey.Value)]
 
 [assembly: InternalsVisibleTo(assemblyName: "Microsoft.ML.StaticPipe" + PublicKey.Value)]
+[assembly: InternalsVisibleTo(assemblyName: "Microsoft.ML.Experimental" + PublicKey.Value)]
 
 [assembly: InternalsVisibleTo(assemblyName: "Microsoft.ML.Internal.MetaLinearLearner" + InternalPublicKey.Value)]
 [assembly: InternalsVisibleTo(assemblyName: "TMSNlearnPrediction" + InternalPublicKey.Value)]

src/Microsoft.ML.Data/Utilities/LocalEnvironment.cs

@@ -93,7 +93,7 @@ private sealed class Host : HostBase
             public Host(HostEnvironmentBase<LocalEnvironment> source, string shortName, string parentFullName, Random rand, bool verbose)
                 : base(source, shortName, parentFullName, rand, verbose)
             {
-                IsCancelled = source.IsCancelled;
+                IsCanceled = source.IsCanceled;
             }
 
             protected override IChannel CreateCommChannel(ChannelProviderBase parent, string name)

src/Microsoft.ML.Experimental/MLContextExtensions.cs

@@ -0,0 +1,15 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+namespace Microsoft.ML.Experimental
+{
+    public static class MLContextExtensions
+    {
+        /// <summary>
+        /// Stop the execution of pipeline in <see cref="MLContext"/>
+        /// </summary>
+        /// <param name="ctx"><see cref="MLContext"/> reference.</param>
+        public static void CancelExecution(this MLContext ctx) => ctx.CancelExecution();
+    }
+}

src/Microsoft.ML.Experimental/Microsoft.ML.Experimental.csproj

@@ -0,0 +1,12 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>netstandard2.0</TargetFramework>
+    <IncludeInPackage>Microsoft.ML.Experimental</IncludeInPackage>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\Microsoft.ML.Data\Microsoft.ML.Data.csproj" />
+  </ItemGroup>
+
+</Project>

test/Microsoft.ML.CodeAnalyzer.Tests/Code/ContractsCheckTest.cs

@@ -39,6 +39,8 @@ public async Task ContractsCheck()
                 VerifyCS.Diagnostic(ContractsCheckAnalyzer.SimpleMessageDiagnostic.Rule).WithLocation(basis + 32, 35).WithArguments("Check", "\"Less fine: \" + env.GetType().Name"),
                 VerifyCS.Diagnostic(ContractsCheckAnalyzer.NameofDiagnostic.Rule).WithLocation(basis + 34, 17).WithArguments("CheckUserArg", "name", "\"p\""),
                 VerifyCS.Diagnostic(ContractsCheckAnalyzer.DecodeMessageWithLoadContextDiagnostic.Rule).WithLocation(basis + 39, 41).WithArguments("CheckDecode", "\"This message is suspicious\""),
+                new DiagnosticResult("CS0122", DiagnosticSeverity.Error).WithLocation("Test1.cs", 752, 24).WithMessage("'ICancelable' is inaccessible due to its protection level"),
+                new DiagnosticResult("CS0122", DiagnosticSeverity.Error).WithLocation("Test1.cs", 752, 67).WithMessage("'ICancelable.IsCanceled' is inaccessible due to its protection level"),
             };
 
             var test = new VerifyCS.Test
@@ -125,7 +127,9 @@ public async Task ContractsCheckFix()
                         VerifyCS.Diagnostic(ContractsCheckAnalyzer.NameofDiagnostic.Rule).WithLocation(23, 39).WithArguments("CheckValue", "paramName", "\"noMatch\""),
                         VerifyCS.Diagnostic(ContractsCheckAnalyzer.NameofDiagnostic.Rule).WithLocation(24, 53).WithArguments("CheckUserArg", "name", "\"chumble\""),
                         VerifyCS.Diagnostic(ContractsCheckAnalyzer.NameofDiagnostic.Rule).WithLocation(25, 53).WithArguments("CheckUserArg", "name", "\"sp\""),
-                        new DiagnosticResult("CS1503", DiagnosticSeverity.Error).WithLocation("Test1.cs", 752, 91).WithMessage("Argument 2: cannot convert from 'Microsoft.ML.Runtime.IHostEnvironment' to 'Microsoft.ML.Runtime.IExceptionContext'"),
+                        new DiagnosticResult("CS0122", DiagnosticSeverity.Error).WithLocation("Test1.cs", 752, 24).WithMessage("'ICancelable' is inaccessible due to its protection level"),
+                        new DiagnosticResult("CS0122", DiagnosticSeverity.Error).WithLocation("Test1.cs", 752, 67).WithMessage("'ICancelable.IsCanceled' is inaccessible due to its protection level"),
+                        new DiagnosticResult("CS1503", DiagnosticSeverity.Error).WithLocation("Test1.cs", 753, 91).WithMessage("Argument 2: cannot convert from 'Microsoft.ML.Runtime.IHostEnvironment' to 'Microsoft.ML.Runtime.IExceptionContext'"),
                     },
                     AdditionalReferences = { AdditionalMetadataReferences.RefFromType<Memory<int>>() },
                 },
@@ -144,7 +148,9 @@ public async Task ContractsCheckFix()
                     {
                         VerifyCS.Diagnostic(ContractsCheckAnalyzer.ExceptionDiagnostic.Rule).WithLocation(9, 43).WithArguments("ExceptParam"),
                         VerifyCS.Diagnostic(ContractsCheckAnalyzer.NameofDiagnostic.Rule).WithLocation(23, 39).WithArguments("CheckValue", "paramName", "\"noMatch\""),
-                        new DiagnosticResult("CS1503", DiagnosticSeverity.Error).WithLocation("Test1.cs", 752, 91).WithMessage("Argument 2: cannot convert from 'Microsoft.ML.Runtime.IHostEnvironment' to 'Microsoft.ML.Runtime.IExceptionContext'"),
+                        new DiagnosticResult("CS0122", DiagnosticSeverity.Error).WithLocation("Test1.cs", 752, 24).WithMessage("'ICancelable' is inaccessible due to its protection level"),
+                        new DiagnosticResult("CS0122", DiagnosticSeverity.Error).WithLocation("Test1.cs", 752, 67).WithMessage("'ICancelable.IsCanceled' is inaccessible due to its protection level"),
+                        new DiagnosticResult("CS1503", DiagnosticSeverity.Error).WithLocation("Test1.cs", 753, 91).WithMessage("Argument 2: cannot convert from 'Microsoft.ML.Runtime.IHostEnvironment' to 'Microsoft.ML.Runtime.IExceptionContext'"),
                     },
                 },
             };

test/Microsoft.ML.CodeAnalyzer.Tests/Resources/ContractsCheckResource.cs

@@ -72,7 +72,6 @@ internal enum MessageSensitivity
     }
     internal interface IHostEnvironment : IExceptionContext
     {
-        bool IsCancelled { get; }
     }
 }