Improves thread safety of lazy initializations

The Interlocked.Exchange calls will ensure that the same object is
returned from each call even under a race.  That's not necessarily
required, but it should also make sure that no write re-ordering issues
occur on platforms that allow it.  And it also makes the possibility
of thread safety issues explicit.

1 files changed, 7 insertions, 2 deletions

diff --git a/Mono.Cecil/GenericInstanceType.cs b/Mono.Cecil/GenericInstanceType.cs
index 8885850..745acd8 100644
--- a/Mono.Cecil/GenericInstanceType.cs
+++ b/Mono.Cecil/GenericInstanceType.cs
@@ -10,7 +10,7 @@
 
 using System;
 using System.Text;
-
+using System.Threading;
 using Mono.Collections.Generic;
 
 using MD = Mono.Cecil.Metadata;
@@ -26,7 +26,12 @@ namespace Mono.Cecil {
 		}
 
 		public Collection<TypeReference> GenericArguments {
-			get { return arguments ?? (arguments = new Collection<TypeReference> ()); }
+			get {
+				if (arguments == null)
+					Interlocked.CompareExchange (ref arguments, new Collection<TypeReference> (), null);
+
+				return arguments;
+			}
 		}
 
 		public override TypeReference DeclaringType {