Threading fixes (#76230)

We have a few theoretical races in some of our threading code, as detailed in #75759. I've audited our uses of ImmutableArray as backing fields for this pattern, fixing it up where I find issues, as well as a couple of other threading issues that I found while looking at things named lazy in our codebase.

Closes #75759

src/Compilers/CSharp/Portable/Emitter/Model/PEModuleBuilder.cs

@@ -613,9 +613,9 @@ private static void GetExportedTypes(NamespaceOrTypeSymbol symbol, int parentInd
 
             if (_lazyExportedTypes.IsDefault)
             {
-                _lazyExportedTypes = CalculateExportedTypes();
+                var initialized = ImmutableInterlocked.InterlockedInitialize(ref _lazyExportedTypes, CalculateExportedTypes());
 
-                if (_lazyExportedTypes.Length > 0)
+                if (initialized && _lazyExportedTypes.Length > 0)
                 {
                     ReportExportedTypeNameCollisions(_lazyExportedTypes, diagnostics);
                 }

src/Compilers/CSharp/Portable/Symbols/Attributes/PEAttributeData.cs

@@ -8,6 +8,7 @@
 using System.Diagnostics.CodeAnalysis;
 using System.Reflection.Metadata;
 using System.Threading;
+using Microsoft.CodeAnalysis.Collections;
 
 namespace Microsoft.CodeAnalysis.CSharp.Symbols.Metadata.PE
 {
@@ -97,7 +98,7 @@ private void EnsureClassAndConstructorSymbolsAreLoaded()
 
         private void EnsureAttributeArgumentsAreLoaded()
         {
-            if (_lazyConstructorArguments.IsDefault || _lazyNamedArguments.IsDefault)
+            if (RoslynImmutableInterlocked.VolatileRead(in _lazyConstructorArguments).IsDefault || RoslynImmutableInterlocked.VolatileRead(in _lazyNamedArguments).IsDefault)
             {
                 TypedConstant[]? lazyConstructorArguments = null;
                 KeyValuePair<string, TypedConstant>[]? lazyNamedArguments = null;

src/Compilers/CSharp/Portable/Symbols/Metadata/PE/PEGlobalNamespaceSymbol.cs

@@ -13,6 +13,7 @@
 using System.Linq;
 using System.Reflection.Metadata;
 using System;
+using System.Threading;
 
 namespace Microsoft.CodeAnalysis.CSharp.Symbols.Metadata.PE
 {
@@ -81,7 +82,7 @@ internal override ModuleSymbol ContainingModule
 
         protected override void EnsureAllMembersLoaded()
         {
-            if (lazyTypes == null || lazyNamespaces == null)
+            if (Volatile.Read(ref lazyTypes) == null || Volatile.Read(ref lazyNamespaces) == null)
             {
                 IEnumerable<IGrouping<string, TypeDefinitionHandle>> groups;
 

src/Compilers/CSharp/Portable/Symbols/Metadata/PE/PEMethodSymbol.cs

@@ -131,24 +131,24 @@ public MethodKind MethodKind
             public bool IsExplicitFinalizerOverride => (_bits & IsExplicitFinalizerOverrideBit) != 0;
             public bool IsExplicitClassOverride => (_bits & IsExplicitClassOverrideBit) != 0;
             public bool IsExplicitOverrideIsPopulated => (_bits & IsExplicitOverrideIsPopulatedBit) != 0;
-            public bool IsObsoleteAttributePopulated => (_bits & IsObsoleteAttributePopulatedBit) != 0;
-            public bool IsCustomAttributesPopulated => (_bits & IsCustomAttributesPopulatedBit) != 0;
-            public bool IsUseSiteDiagnosticPopulated => (_bits & IsUseSiteDiagnosticPopulatedBit) != 0;
-            public bool IsConditionalPopulated => (_bits & IsConditionalPopulatedBit) != 0;
-            public bool IsOverriddenOrHiddenMembersPopulated => (_bits & IsOverriddenOrHiddenMembersPopulatedBit) != 0;
+            public bool IsObsoleteAttributePopulated => (Volatile.Read(ref _bits) & IsObsoleteAttributePopulatedBit) != 0;
+            public bool IsCustomAttributesPopulated => (Volatile.Read(ref _bits) & IsCustomAttributesPopulatedBit) != 0;
+            public bool IsUseSiteDiagnosticPopulated => (Volatile.Read(ref _bits) & IsUseSiteDiagnosticPopulatedBit) != 0;
+            public bool IsConditionalPopulated => (Volatile.Read(ref _bits) & IsConditionalPopulatedBit) != 0;
+            public bool IsOverriddenOrHiddenMembersPopulated => (Volatile.Read(ref _bits) & IsOverriddenOrHiddenMembersPopulatedBit) != 0;
             public bool IsReadOnly => (_bits & IsReadOnlyBit) != 0;
             public bool IsReadOnlyPopulated => (_bits & IsReadOnlyPopulatedBit) != 0;
             public bool DoesNotReturn => (_bits & DoesNotReturnBit) != 0;
             public bool IsDoesNotReturnPopulated => (_bits & IsDoesNotReturnPopulatedBit) != 0;
-            public bool IsMemberNotNullPopulated => (_bits & IsMemberNotNullPopulatedBit) != 0;
+            public bool IsMemberNotNullPopulated => (Volatile.Read(ref _bits) & IsMemberNotNullPopulatedBit) != 0;
             public bool IsInitOnly => (_bits & IsInitOnlyBit) != 0;
             public bool IsInitOnlyPopulated => (_bits & IsInitOnlyPopulatedBit) != 0;
-            public bool IsUnmanagedCallersOnlyAttributePopulated => (_bits & IsUnmanagedCallersOnlyAttributePopulatedBit) != 0;
+            public bool IsUnmanagedCallersOnlyAttributePopulated => (Volatile.Read(ref _bits) & IsUnmanagedCallersOnlyAttributePopulatedBit) != 0;
             public bool HasSetsRequiredMembers => (_bits & HasSetsRequiredMembersBit) != 0;
             public bool HasSetsRequiredMembersPopulated => (_bits & HasSetsRequiredMembersPopulatedBit) != 0;
             public bool IsUnscopedRef => (_bits & IsUnscopedRefBit) != 0;
             public bool IsUnscopedRefPopulated => (_bits & IsUnscopedRefPopulatedBit) != 0;
-            public bool IsOverloadResolutionPriorityPopulated => (_bits & OverloadResolutionPriorityPopulatedBit) != 0;
+            public bool IsOverloadResolutionPriorityPopulated => (Volatile.Read(ref _bits) & OverloadResolutionPriorityPopulatedBit) != 0;
 
 #if DEBUG
             static PackedFlags()

src/Compilers/CSharp/Portable/Symbols/Metadata/PE/PENamedTypeSymbol.cs

@@ -15,6 +15,7 @@
 using System.Reflection.Metadata.Ecma335;
 using System.Runtime.InteropServices;
 using System.Threading;
+using Microsoft.CodeAnalysis.Collections;
 using Microsoft.CodeAnalysis.CSharp.DocumentationComments;
 using Microsoft.CodeAnalysis.CSharp.Emit;
 using Microsoft.CodeAnalysis.PooledObjects;
@@ -1260,7 +1261,7 @@ private void EnsureEnumUnderlyingTypeIsLoaded(UncommonProperties uncommon)
 
         private void EnsureAllMembersAreLoaded()
         {
-            if (_lazyMembersByName == null)
+            if (Volatile.Read(ref _lazyMembersByName) == null)
             {
                 LoadMembers();
             }
@@ -1270,7 +1271,7 @@ private void LoadMembers()
         {
             ArrayBuilder<Symbol> members = null;
 
-            if (_lazyMembersInDeclarationOrder.IsDefault)
+            if (RoslynImmutableInterlocked.VolatileRead(ref _lazyMembersInDeclarationOrder).IsDefault)
             {
                 EnsureNestedTypesAreLoaded();
 
@@ -1440,7 +1441,7 @@ private void LoadMembers()
                 }
             }
 
-            if (_lazyMembersByName == null)
+            if (Volatile.Read(ref _lazyMembersByName) == null)
             {
                 if (members == null)
                 {

src/Compilers/CSharp/Portable/Symbols/Metadata/PE/PENestedNamespaceSymbol.cs

@@ -125,11 +125,14 @@ internal override ModuleSymbol ContainingModule
 
         protected override void EnsureAllMembersLoaded()
         {
-            var typesByNS = _typesByNS;
+            var typesByNS = Volatile.Read(ref _typesByNS);
 
-            if (lazyTypes == null || lazyNamespaces == null)
+            if (typesByNS == null)
+            {
+                Debug.Assert(lazyNamespaces != null && lazyTypes != null);
+            }
+            else
             {
-                System.Diagnostics.Debug.Assert(typesByNS != null);
                 LoadAllMembers(typesByNS);
                 Interlocked.Exchange(ref _typesByNS, null);
             }

src/Compilers/CSharp/Portable/Symbols/Metadata/PE/PEPropertySymbol.cs

@@ -128,28 +128,28 @@ public void SetUseSiteDiagnosticPopulated()
                 ThreadSafeFlagOperations.Set(ref _bits, IsUseSiteDiagnosticPopulatedBit);
             }
 
-            public readonly bool IsUseSiteDiagnosticPopulated => (_bits & IsUseSiteDiagnosticPopulatedBit) != 0;
+            public bool IsUseSiteDiagnosticPopulated => (Volatile.Read(ref _bits) & IsUseSiteDiagnosticPopulatedBit) != 0;
 
             public void SetObsoleteAttributePopulated()
             {
                 ThreadSafeFlagOperations.Set(ref _bits, IsObsoleteAttributePopulatedBit);
             }
 
-            public readonly bool IsObsoleteAttributePopulated => (_bits & IsObsoleteAttributePopulatedBit) != 0;
+            public bool IsObsoleteAttributePopulated => (Volatile.Read(ref _bits) & IsObsoleteAttributePopulatedBit) != 0;
 
             public void SetCustomAttributesPopulated()
             {
                 ThreadSafeFlagOperations.Set(ref _bits, IsCustomAttributesPopulatedBit);
             }
 
-            public readonly bool IsCustomAttributesPopulated => (_bits & IsCustomAttributesPopulatedBit) != 0;
+            public bool IsCustomAttributesPopulated => (Volatile.Read(ref _bits) & IsCustomAttributesPopulatedBit) != 0;
 
             public void SetOverloadResolutionPriorityPopulated()
             {
                 ThreadSafeFlagOperations.Set(ref _bits, IsOverloadResolutionPriorityPopulatedBit);
             }
 
-            public readonly bool IsOverloadResolutionPriorityPopulated => (_bits & IsOverloadResolutionPriorityPopulatedBit) != 0;
+            public bool IsOverloadResolutionPriorityPopulated => (Volatile.Read(ref _bits) & IsOverloadResolutionPriorityPopulatedBit) != 0;
         }
 
         /// <summary>

src/Compilers/CSharp/Portable/Symbols/Metadata/PE/PETypeParameterSymbol.cs

@@ -12,6 +12,7 @@
 using System.Reflection.Metadata;
 using System.Reflection.Metadata.Ecma335;
 using System.Threading;
+using Microsoft.CodeAnalysis.Collections;
 using Microsoft.CodeAnalysis.PooledObjects;
 using Roslyn.Utilities;
 
@@ -152,7 +153,7 @@ private ImmutableArray<TypeWithAnnotations> GetDeclaredConstraintTypes(ConsList<
             Debug.Assert(!inProgress.ContainsReference(this));
             Debug.Assert(!inProgress.Any() || ReferenceEquals(inProgress.Head.ContainingSymbol, this.ContainingSymbol));
 
-            if (_lazyDeclaredConstraintTypes.IsDefault)
+            if (RoslynImmutableInterlocked.VolatileRead(ref _lazyDeclaredConstraintTypes).IsDefault)
             {
                 ImmutableArray<TypeWithAnnotations> declaredConstraintTypes;
 

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

@@ -7,6 +7,7 @@
 using System.Diagnostics;
 using System.Threading;
 using Microsoft.Cci;
+using Microsoft.CodeAnalysis.Collections;
 using Microsoft.CodeAnalysis.CSharp.Syntax;
 using Microsoft.CodeAnalysis.PooledObjects;
 using Roslyn.Utilities;
@@ -181,7 +182,7 @@ public override ImmutableArray<ParameterSymbol> Parameters
 
         private void ComputeParameters()
         {
-            if (_lazyParameters != null)
+            if (!RoslynImmutableInterlocked.VolatileRead(in _lazyParameters).IsDefault)
             {
                 return;
             }
@@ -211,7 +212,7 @@ private void ComputeParameters()
 
             lock (_declarationDiagnostics)
             {
-                if (_lazyParameters != null)
+                if (!_lazyParameters.IsDefault)
                 {
                     diagnostics.Free();
                     return;
@@ -221,7 +222,7 @@ private void ComputeParameters()
                 _declarationDependencies.AddAll(diagnostics.DependenciesBag);
                 diagnostics.Free();
                 _lazyIsVarArg = isVararg;
-                _lazyParameters = parameters;
+                RoslynImmutableInterlocked.VolatileWrite(ref _lazyParameters, parameters);
             }
         }
 

src/Compilers/CSharp/Portable/Symbols/SubstitutedMethodSymbol.cs

@@ -7,6 +7,7 @@
 using System.Collections.Immutable;
 using System.Diagnostics;
 using System.Threading;
+using Microsoft.CodeAnalysis.Collections;
 using Microsoft.CodeAnalysis.PooledObjects;
 using Roslyn.Utilities;
 
@@ -99,7 +100,7 @@ public sealed override ImmutableArray<TypeParameterSymbol> TypeParameters
 
         private void EnsureMapAndTypeParameters()
         {
-            if (!_lazyTypeParameters.IsDefault)
+            if (!RoslynImmutableInterlocked.VolatileRead(ref _lazyTypeParameters).IsDefault)
             {
                 return;
             }

src/Compilers/CSharp/Portable/Symbols/SubstitutedNamedTypeSymbol.cs

@@ -10,6 +10,7 @@
 using System.Diagnostics;
 using System.Linq;
 using System.Threading;
+using Microsoft.CodeAnalysis.Collections;
 using Microsoft.CodeAnalysis.CSharp.Emit;
 using Microsoft.CodeAnalysis.PooledObjects;
 using Roslyn.Utilities;
@@ -96,7 +97,7 @@ public sealed override ImmutableArray<TypeParameterSymbol> TypeParameters
 
         private void EnsureMapAndTypeParameters()
         {
-            if (!_lazyTypeParameters.IsDefault)
+            if (!RoslynImmutableInterlocked.VolatileRead(ref _lazyTypeParameters).IsDefault)
             {
                 return;
             }

src/Compilers/Core/Portable/Syntax/SyntaxTree.cs

@@ -10,6 +10,7 @@
 using System.Text;
 using System.Threading;
 using System.Threading.Tasks;
+using Microsoft.CodeAnalysis.Collections;
 using Microsoft.CodeAnalysis.Text;
 using Roslyn.Utilities;
 
@@ -369,11 +370,11 @@ internal int GetDisplayLineNumber(TextSpan span)
         /// </summary>
         internal Cci.DebugSourceInfo GetDebugSourceInfo()
         {
-            if (_lazyChecksum.IsDefault)
+            if (RoslynImmutableInterlocked.VolatileRead(ref _lazyChecksum).IsDefault)
             {
                 var text = this.GetText();
-                _lazyChecksum = text.GetChecksum();
                 _lazyHashAlgorithm = text.ChecksumAlgorithm;
+                ImmutableInterlocked.InterlockedInitialize(ref _lazyChecksum, text.GetChecksum());
             }
 
             Debug.Assert(!_lazyChecksum.IsDefault);

src/Compilers/VisualBasic/Portable/BoundTree/BoundMethodGroup.vb

@@ -8,6 +8,7 @@ Imports Microsoft.CodeAnalysis.VisualBasic.Symbols
 Imports Microsoft.CodeAnalysis.VisualBasic.Syntax
 Imports System.Runtime.InteropServices
 Imports System.Threading
+Imports Microsoft.CodeAnalysis.Collections
 
 Namespace Microsoft.CodeAnalysis.VisualBasic
 
@@ -55,7 +56,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
             Debug.Assert(group.PendingExtensionMethodsOpt Is Me)
             Debug.Assert(Not useSiteInfo.AccumulatesDependencies OrElse _withDependencies)
 
-            If _lazyMethods.IsDefault Then
+            If RoslynImmutableInterlocked.VolatileRead(_lazyMethods).IsDefault Then
                 Dim receiverOpt As BoundExpression = group.ReceiverOpt
                 Dim methods As ImmutableArray(Of MethodSymbol) = ImmutableArray(Of MethodSymbol).Empty
                 Dim localUseSiteInfo = If(_withDependencies, New CompoundUseSiteInfo(Of AssemblySymbol)(_lookupBinder.Compilation.Assembly), CompoundUseSiteInfo(Of AssemblySymbol).DiscardedDependencies)

src/Compilers/VisualBasic/Portable/Emit/PEModuleBuilder.vb

@@ -386,9 +386,9 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Emit
             Debug.Assert(HaveDeterminedTopLevelTypes)
 
             If _lazyExportedTypes.IsDefault Then
-                _lazyExportedTypes = CalculateExportedTypes()
+                Dim initialized = ImmutableInterlocked.InterlockedInitialize(_lazyExportedTypes, CalculateExportedTypes())
 
-                If _lazyExportedTypes.Length > 0 Then
+                If initialized AndAlso _lazyExportedTypes.Length > 0 Then
                     ReportExportedTypeNameCollisions(_lazyExportedTypes, diagnostics)
                 End If
             End If

src/Compilers/VisualBasic/Portable/Symbols/Attributes/PEAttributeData.vb

@@ -120,7 +120,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Symbols.Metadata.PE
 
         Private Sub EnsureLazyMembersAreLoaded()
 
-            If _lazyConstructorArguments Is Nothing Then
+            If Volatile.Read(_lazyConstructorArguments) Is Nothing Then
 
                 Dim constructorArgs As TypedConstant() = Nothing
                 Dim namedArgs As KeyValuePair(Of String, TypedConstant)() = Nothing

src/Compilers/VisualBasic/Portable/Symbols/Metadata/PE/PEGlobalNamespaceSymbol.vb

@@ -7,6 +7,7 @@ Imports Microsoft.CodeAnalysis.Text
 Imports Microsoft.CodeAnalysis.VisualBasic.Symbols
 Imports Microsoft.CodeAnalysis.VisualBasic.Syntax
 Imports System.Reflection.Metadata
+Imports System.Threading
 
 Namespace Microsoft.CodeAnalysis.VisualBasic.Symbols.Metadata.PE
 
@@ -61,7 +62,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Symbols.Metadata.PE
         End Property
 
         Protected Overrides Sub EnsureAllMembersLoaded()
-            If m_lazyTypes Is Nothing OrElse m_lazyMembers Is Nothing Then
+            If Volatile.Read(m_lazyTypes) Is Nothing OrElse Volatile.Read(m_lazyMembers) Is Nothing Then
                 Dim groups As IEnumerable(Of IGrouping(Of String, TypeDefinitionHandle))
 
                 Try

src/Compilers/VisualBasic/Portable/Symbols/Metadata/PE/PEMethodSymbol.vb

@@ -113,25 +113,25 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Symbols.Metadata.PE
 
             Public ReadOnly Property IsObsoleteAttributePopulated As Boolean
                 Get
-                    Return (_bits And s_isObsoleteAttributePopulatedBit) <> 0
+                    Return (Volatile.Read(_bits) And s_isObsoleteAttributePopulatedBit) <> 0
                 End Get
             End Property
 
             Public ReadOnly Property IsCustomAttributesPopulated As Boolean
                 Get
-                    Return (_bits And s_isCustomAttributesPopulatedBit) <> 0
+                    Return (Volatile.Read(_bits) And s_isCustomAttributesPopulatedBit) <> 0
                 End Get
             End Property
 
             Public ReadOnly Property IsUseSiteDiagnosticPopulated As Boolean
                 Get
-                    Return (_bits And s_isUseSiteDiagnosticPopulatedBit) <> 0
+                    Return (Volatile.Read(_bits) And s_isUseSiteDiagnosticPopulatedBit) <> 0
                 End Get
             End Property
 
             Public ReadOnly Property IsConditionalPopulated As Boolean
                 Get
-                    Return (_bits And s_isConditionalAttributePopulatedBit) <> 0
+                    Return (Volatile.Read(_bits) And s_isConditionalAttributePopulatedBit) <> 0
                 End Get
             End Property
 

src/Compilers/VisualBasic/Portable/Symbols/Metadata/PE/PENamedTypeSymbol.vb

@@ -649,7 +649,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Symbols.Metadata.PE
 
         Private Sub EnsureNonTypeMembersAreLoaded()
 
-            If _lazyMembers Is Nothing Then
+            If Volatile.Read(_lazyMembers) Is Nothing Then
                 ' A method may be referenced as an accessor by one or more properties. And,
                 ' any of those properties may be "bogus" if one of the property accessors
                 ' does not match the property signature. If the method is referenced by at

src/Compilers/VisualBasic/Portable/Symbols/Metadata/PE/PENestedNamespaceSymbol.vb

@@ -118,10 +118,11 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Symbols.Metadata.PE
         End Property
 
         Protected Overrides Sub EnsureAllMembersLoaded()
-            Dim typesByNS = _typesByNS
+            Dim typesByNS = Volatile.Read(_typesByNS)
 
-            If m_lazyTypes Is Nothing OrElse m_lazyMembers Is Nothing Then
-                Debug.Assert(typesByNS IsNot Nothing)
+            If typesByNS Is Nothing Then
+                Debug.Assert(m_lazyTypes IsNot Nothing AndAlso m_lazyMembers IsNot Nothing)
+            Else
                 LoadAllMembers(typesByNS)
                 Interlocked.Exchange(_typesByNS, Nothing)
             End If