Make EqualityComparer thread-safe for Mono (dotnet#31990)

* Make EqualityComparer thread-safe for Mono Fixes dotnet#3009 Fixes dotnet#31988 * Use Interlocked.CompareExchange
realmar · Feb 9, 2020 · a1bc3cc · a1bc3cc
1 parent 3b72a4d
commit a1bc3cc
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Showing 2 changed files with 17 additions and 13 deletions.
diff --git a/src/mono/netcore/System.Private.CoreLib/src/System/Collections/Generic/Comparer.Mono.cs b/src/mono/netcore/System.Private.CoreLib/src/System/Collections/Generic/Comparer.Mono.cs
@@ -3,29 +3,31 @@
 // See the LICENSE file in the project root for more information.
 
 using System.Runtime.CompilerServices;
+using System.Threading;
 
 namespace System.Collections.Generic
 {
 	partial class Comparer<T>
 	{
-        static volatile Comparer<T> defaultComparer;
+		static volatile Comparer<T> defaultComparer;
 
 		public static Comparer<T> Default {
 			get {
-                Comparer<T> comparer = defaultComparer;
-                if (comparer == null) {
-                    comparer = CreateComparer();
-                    defaultComparer = comparer;
-                }
-                return comparer;
+				Comparer<T> comparer = defaultComparer;
+				if (comparer == null) {
+					// Do not use static constructor. Generic static constructors are problematic for Mono AOT.
+					Interlocked.CompareExchange(ref defaultComparer, CreateComparer(), null);
+					comparer = defaultComparer;
+				}
+				return comparer;
 			}
 		}
 
-        static Comparer<T> CreateComparer() {
-            RuntimeType t = (RuntimeType)typeof(T);
+		static Comparer<T> CreateComparer() {
+			RuntimeType t = (RuntimeType)typeof(T);
 
-                if (typeof(IComparable<T>).IsAssignableFrom(t))
-                    return (Comparer<T>)RuntimeType.CreateInstanceForAnotherGenericParameter (typeof(GenericComparer<>), t);
+				if (typeof(IComparable<T>).IsAssignableFrom(t))
+					return (Comparer<T>)RuntimeType.CreateInstanceForAnotherGenericParameter (typeof(GenericComparer<>), t);
 
 				// If T is a Nullable<U> where U implements IComparable<U> return a NullableComparer<U>
 				if (t.IsGenericType && t.GetGenericTypeDefinition() == typeof(Nullable<>)) {

diff --git a/...no/netcore/System.Private.CoreLib/src/System/Collections/Generic/EqualityComparer.Mono.cs b/...no/netcore/System.Private.CoreLib/src/System/Collections/Generic/EqualityComparer.Mono.cs
@@ -3,6 +3,7 @@
 // See the LICENSE file in the project root for more information.
 
 using System.Runtime.CompilerServices;
+using System.Threading;
 
 namespace System.Collections.Generic
 {
@@ -15,8 +16,9 @@ public static EqualityComparer<T> Default {
 			get {
 				EqualityComparer<T> comparer = defaultComparer;
 				if (comparer == null) {
-					comparer = CreateComparer();
-					defaultComparer = comparer;
+					// Do not use static constructor. Generic static constructors are problematic for Mono AOT.
+					Interlocked.CompareExchange(ref defaultComparer, CreateComparer(), null);
+					comparer = defaultComparer;
 				}
 				return comparer;
 			}