Simplify common calls to Parallel.For with a RoslynParallel.For helper

src/Compilers/CSharp/Portable/CommandLine/CSharpCompiler.cs

@@ -11,13 +11,12 @@
 using System.IO;
 using System.Linq;
 using System.Threading;
-using System.Threading.Tasks;
+using Microsoft.CodeAnalysis;
 using Microsoft.CodeAnalysis.Collections;
+using Microsoft.CodeAnalysis.CSharp.Syntax;
 using Microsoft.CodeAnalysis.Diagnostics;
 using Microsoft.CodeAnalysis.Text;
 using Roslyn.Utilities;
-using Microsoft.CodeAnalysis.CSharp.Syntax;
-using Microsoft.CodeAnalysis;
 
 namespace Microsoft.CodeAnalysis.CSharp
 {
@@ -60,9 +59,10 @@ protected CSharpCompiler(CSharpCommandLineParser parser, string responseFile, st
 
             if (Arguments.CompilationOptions.ConcurrentBuild)
             {
-                Parallel.For(0, sourceFiles.Length, UICultureUtilities.WithCurrentUICulture<int>(i =>
-                {
-                    try
+                RoslynParallel.For(
+                    0,
+                    sourceFiles.Length,
+                    UICultureUtilities.WithCurrentUICulture<int>(i =>
                     {
                         //NOTE: order of trees is important!!
                         trees[i] = ParseFile(
@@ -72,12 +72,8 @@ protected CSharpCompiler(CSharpCommandLineParser parser, string responseFile, st
                             sourceFiles[i],
                             diagnosticBag,
                             out normalizedFilePaths[i]);
-                    }
-                    catch (Exception e) when (FatalError.Report(e))
-                    {
-                        throw ExceptionUtilities.Unreachable;
-                    }
-                }));
+                    }),
+                    CancellationToken.None);
             }
             else
             {

src/Compilers/CSharp/Portable/Compilation/CSharpCompilation.cs

@@ -51,8 +51,6 @@ public sealed partial class CSharpCompilation : Compilation
         //
         // !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
 
-        internal static readonly ParallelOptions DefaultParallelOptions = new ParallelOptions();
-
         private readonly CSharpCompilationOptions _options;
         private readonly Lazy<Imports> _globalImports;
         private readonly Lazy<Imports> _previousSubmissionImports;
@@ -2472,31 +2470,16 @@ internal override void GetDiagnostics(CompilationStage stage, bool includeEarlie
                 var syntaxTrees = this.SyntaxTrees;
                 if (this.Options.ConcurrentBuild)
                 {
-                    var parallelOptions = cancellationToken.CanBeCanceled
-                                        ? new ParallelOptions() { CancellationToken = cancellationToken }
-                                        : DefaultParallelOptions;
-
-                    Parallel.For(0, syntaxTrees.Length, parallelOptions,
+                    RoslynParallel.For(
+                        0,
+                        syntaxTrees.Length,
                         UICultureUtilities.WithCurrentUICulture<int>(i =>
                         {
-                            try
-                            {
-                                var syntaxTree = syntaxTrees[i];
-                                AppendLoadDirectiveDiagnostics(builder, _syntaxAndDeclarations, syntaxTree);
-                                builder.AddRange(syntaxTree.GetDiagnostics(cancellationToken));
-                            }
-                            catch (Exception e) when (FatalError.ReportUnlessCanceled(e))
-                            {
-                                throw ExceptionUtilities.Unreachable;
-                            }
-                            catch (OperationCanceledException e) when (cancellationToken.IsCancellationRequested && e.CancellationToken != cancellationToken)
-                            {
-                                // Parallel.For checks for a specific cancellation token, so make sure we throw with the
-                                // correct one.
-                                cancellationToken.ThrowIfCancellationRequested();
-                                throw ExceptionUtilities.Unreachable;
-                            }
-                        }));
+                            var syntaxTree = syntaxTrees[i];
+                            AppendLoadDirectiveDiagnostics(builder, _syntaxAndDeclarations, syntaxTree);
+                            builder.AddRange(syntaxTree.GetDiagnostics(cancellationToken));
+                        }),
+                        cancellationToken);
                 }
                 else
                 {

src/Compilers/CSharp/Portable/Symbols/Source/SourceNamespaceSymbol_Completion.cs

@@ -2,14 +2,8 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
-using Microsoft.CodeAnalysis.CSharp.Symbols;
-using Microsoft.CodeAnalysis.CSharp.Syntax;
-using Microsoft.CodeAnalysis.Text;
-using Roslyn.Utilities;
-using System;
-using System.Diagnostics;
 using System.Threading;
-using System.Threading.Tasks;
+using Roslyn.Utilities;
 
 namespace Microsoft.CodeAnalysis.CSharp.Symbols
 {
@@ -49,29 +43,11 @@ internal override void ForceComplete(SourceLocation locationOpt, CancellationTok
 
                             if (this.DeclaringCompilation.Options.ConcurrentBuild)
                             {
-                                var po = cancellationToken.CanBeCanceled
-                                    ? new ParallelOptions() { CancellationToken = cancellationToken }
-                                    : CSharpCompilation.DefaultParallelOptions;
-
-                                Parallel.For(0, members.Length, po, UICultureUtilities.WithCurrentUICulture<int>(i =>
-                                {
-                                    try
-                                    {
-                                        var member = members[i];
-                                        ForceCompleteMemberByLocation(locationOpt, member, cancellationToken);
-                                    }
-                                    catch (Exception e) when (FatalError.ReportUnlessCanceled(e))
-                                    {
-                                        throw ExceptionUtilities.Unreachable;
-                                    }
-                                    catch (OperationCanceledException e) when (cancellationToken.IsCancellationRequested && e.CancellationToken != cancellationToken)
-                                    {
-                                        // Parallel.For checks for a specific cancellation token, so make sure we throw with the
-                                        // correct one.
-                                        cancellationToken.ThrowIfCancellationRequested();
-                                        throw ExceptionUtilities.Unreachable;
-                                    }
-                                }));
+                                RoslynParallel.For(
+                                    0,
+                                    members.Length,
+                                    UICultureUtilities.WithCurrentUICulture<int>(i => ForceCompleteMemberByLocation(locationOpt, members[i], cancellationToken)),
+                                    cancellationToken);
 
                                 foreach (var member in members)
                                 {

src/Compilers/Core/Portable/InternalUtilities/RoslynParallel.cs

+// 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.
+
+using System;
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.CodeAnalysis;
+
+namespace Roslyn.Utilities
+{
+    internal static class RoslynParallel
+    {
+        internal static readonly ParallelOptions DefaultParallelOptions = new ParallelOptions();
+
+        /// <inheritdoc cref="Parallel.For(int, int, ParallelOptions, Action{int})"/>
+        public static ParallelLoopResult For(int fromInclusive, int toExclusive, Action<int> body, CancellationToken cancellationToken)
+        {
+            var parallelOptions = cancellationToken.CanBeCanceled
+                ? new ParallelOptions { CancellationToken = cancellationToken }
+                : DefaultParallelOptions;
+
+            return Parallel.For(fromInclusive, toExclusive, parallelOptions, errorHandlingBody);
+
+            // Local function
+            void errorHandlingBody(int i)
+            {
+                try
+                {
+                    body(i);
+                }
+                catch (Exception e) when (FatalError.ReportUnlessCanceled(e, cancellationToken))
+                {
+                    throw ExceptionUtilities.Unreachable;
+                }
+                catch (OperationCanceledException e) when (cancellationToken.IsCancellationRequested && e.CancellationToken != cancellationToken)
+                {
+                    // Parallel.For checks for a specific cancellation token, so make sure we throw with the
+                    // correct one.
+                    cancellationToken.ThrowIfCancellationRequested();
+                    throw ExceptionUtilities.Unreachable;
+                }
+            }
+        }
+    }
+}

src/Compilers/VisualBasic/Portable/CommandLine/VisualBasicCompiler.vb

@@ -4,6 +4,7 @@
 
 Imports System.Collections.Immutable
 Imports System.IO
+Imports System.Threading
 Imports Microsoft.CodeAnalysis.Collections
 Imports Microsoft.CodeAnalysis.Diagnostics
 Imports Microsoft.CodeAnalysis.VisualBasic.Syntax
@@ -99,22 +100,21 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
             Dim trees(sourceFiles.Length - 1) As SyntaxTree
 
             If Arguments.CompilationOptions.ConcurrentBuild Then
-                Parallel.For(0, sourceFiles.Length,
-                   UICultureUtilities.WithCurrentUICulture(Of Integer)(
+                RoslynParallel.For(
+                    0,
+                    sourceFiles.Length,
+                    UICultureUtilities.WithCurrentUICulture(Of Integer)(
                         Sub(i As Integer)
-                            Try
-                                ' NOTE: order of trees is important!!
-                                trees(i) = ParseFile(
+                            ' NOTE: order of trees is important!!
+                            trees(i) = ParseFile(
                                 consoleOutput,
                                 parseOptions,
                                 scriptParseOptions,
                                 hadErrors,
                                 sourceFiles(i),
                                 errorLogger)
-                            Catch ex As Exception When FatalError.Report(ex)
-                                Throw ExceptionUtilities.Unreachable
-                            End Try
-                        End Sub))
+                        End Sub),
+                    CancellationToken.None)
             Else
                 For i = 0 To sourceFiles.Length - 1
                     ' NOTE: order of trees is important!!

src/Compilers/VisualBasic/Portable/Compilation/VisualBasicCompilation.vb

@@ -2087,20 +2087,14 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
                 ' Embedded trees shouldn't have any errors, let's avoid making decision if they should be added too early.
                 ' Otherwise IDE performance might be affect.
                 If Options.ConcurrentBuild Then
-                    Dim options = New ParallelOptions() With {.CancellationToken = cancellationToken}
-                    Parallel.For(0, SyntaxTrees.Length, options, UICultureUtilities.WithCurrentUICulture(
-                        Sub(i As Integer)
-                            Try
+                    RoslynParallel.For(
+                        0,
+                        SyntaxTrees.Length,
+                        UICultureUtilities.WithCurrentUICulture(
+                            Sub(i As Integer)
                                 builder.AddRange(SyntaxTrees(i).GetDiagnostics(cancellationToken))
-                            Catch e As Exception When FatalError.ReportUnlessCanceled(e)
-                                Throw ExceptionUtilities.Unreachable
-                            Catch e As OperationCanceledException When cancellationToken.IsCancellationRequested AndAlso e.CancellationToken <> cancellationToken
-                                ' Parallel.For checks for a specific cancellation token, so make sure we throw with the
-                                ' correct one.
-                                cancellationToken.ThrowIfCancellationRequested()
-                                Throw ExceptionUtilities.Unreachable
-                            End Try
-                        End Sub))
+                            End Sub),
+                        cancellationToken)
                 Else
                     For Each tree In SyntaxTrees
                         cancellationToken.ThrowIfCancellationRequested()

src/Compilers/VisualBasic/Portable/Symbols/Source/SourceModuleSymbol.vb

@@ -616,22 +616,14 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Symbols
                 Dim trees = ArrayBuilder(Of SyntaxTree).GetInstance()
                 trees.AddRange(SyntaxTrees)
 
-                Dim options = New ParallelOptions() With {.CancellationToken = cancellationToken}
-                Parallel.For(0, trees.Count, options,
+                RoslynParallel.For(
+                    0,
+                    trees.Count,
                     UICultureUtilities.WithCurrentUICulture(
                         Sub(i As Integer)
-                            Try
-                                cancellationToken.ThrowIfCancellationRequested()
-                                TryGetSourceFile(trees(i)).GenerateAllDeclarationErrors()
-                            Catch e As Exception When FatalError.ReportUnlessCanceled(e)
-                                Throw ExceptionUtilities.Unreachable
-                            Catch e As OperationCanceledException When cancellationToken.IsCancellationRequested AndAlso e.CancellationToken <> cancellationToken
-                                ' Parallel.For checks for a specific cancellation token, so make sure we throw with the
-                                ' correct one.
-                                cancellationToken.ThrowIfCancellationRequested()
-                                Throw ExceptionUtilities.Unreachable
-                            End Try
-                        End Sub))
+                            TryGetSourceFile(trees(i)).GenerateAllDeclarationErrors()
+                        End Sub),
+                    cancellationToken)
                 trees.Free()
             Else
                 For Each tree In SyntaxTrees