edit: $/Dev10/feature/vs_langs01/Merlin/Main/Languages/Ruby/Libraries.LCA_RESTRICTED/Initializers.Generated.cs;C691193
File: Initializers.Generated.cs
===================================================================
--- $/Dev10/feature/vs_langs01/Merlin/Main/Languages/Ruby/Libraries.LCA_RESTRICTED/Initializers.Generated.cs;C691193  (server)    1/5/2009 10:05 AM
+++ Shelved Change: $/Dev10/feature/vs_langs01/Merlin/Main/Languages/Ruby/Libraries.LCA_RESTRICTED/Initializers.Generated.cs;critical
@@ -5167,11 +5167,11 @@
             });
             
             module.DefineLibraryMethod("critical", 0x61, new System.Delegate[] {
-                new System.Func<System.Object, System.Boolean>(IronRuby.Builtins.ThreadOps.Critical),
+                new System.Func<IronRuby.Runtime.RubyContext, System.Object, System.Boolean>(IronRuby.Builtins.ThreadOps.Critical),
             });
             
             module.DefineLibraryMethod("critical=", 0x61, new System.Delegate[] {
-                new System.Func<System.Object, System.Boolean, System.Boolean>(IronRuby.Builtins.ThreadOps.Critical),
+                new System.Action<IronRuby.Runtime.RubyContext, System.Object, System.Boolean>(IronRuby.Builtins.ThreadOps.Critical),
             });
             
             module.DefineLibraryMethod("current", 0x61, new System.Delegate[] {
@@ -5199,7 +5199,7 @@
             });
             
             module.DefineLibraryMethod("stop", 0x61, new System.Delegate[] {
-                new System.Action<System.Object>(IronRuby.Builtins.ThreadOps.Stop),
+                new System.Action<IronRuby.Runtime.RubyContext, System.Object>(IronRuby.Builtins.ThreadOps.Stop),
             });
             
         }
===================================================================
edit: $/Dev10/feature/vs_langs01/Merlin/Main/Languages/Ruby/Libraries.LCA_RESTRICTED/Builtins/KernelOps.cs;C691193
File: KernelOps.cs
===================================================================
--- $/Dev10/feature/vs_langs01/Merlin/Main/Languages/Ruby/Libraries.LCA_RESTRICTED/Builtins/KernelOps.cs;C691193  (server)    1/5/2009 10:54 AM
+++ Shelved Change: $/Dev10/feature/vs_langs01/Merlin/Main/Languages/Ruby/Libraries.LCA_RESTRICTED/Builtins/KernelOps.cs;critical
@@ -809,7 +809,7 @@
         [RubyMethod("sleep", RubyMethodAttributes.PrivateInstance)]
         [RubyMethod("sleep", RubyMethodAttributes.PublicSingleton)]
         public static void Sleep(object self) {
-            ThreadOps.Stop(Thread.CurrentThread);
+            ThreadOps.DoSleep();
         }
 
         [RubyMethod("sleep", RubyMethodAttributes.PrivateInstance)]
===================================================================
edit: $/Dev10/feature/vs_langs01/Merlin/Main/Languages/Ruby/Libraries.LCA_RESTRICTED/Builtins/ThreadOps.cs;C691193
File: ThreadOps.cs
===================================================================
--- $/Dev10/feature/vs_langs01/Merlin/Main/Languages/Ruby/Libraries.LCA_RESTRICTED/Builtins/ThreadOps.cs;C691193  (server)    1/4/2009 11:36 PM
+++ Shelved Change: $/Dev10/feature/vs_langs01/Merlin/Main/Languages/Ruby/Libraries.LCA_RESTRICTED/Builtins/ThreadOps.cs;critical
@@ -540,19 +540,22 @@
             return value;
         }
 
-        //    critical
-        //    critical=
-
         [RubyMethod("critical", RubyMethodAttributes.PublicSingleton)]
-        public static bool Critical(object self) {
+        public static bool Critical(RubyContext/*!*/ context, object self) {
             RubyThreadInfo.RegisterThread(Thread.CurrentThread);
-            return false;
+            return context.IsInCriticalRegion;
         }
 
         [RubyMethod("critical=", RubyMethodAttributes.PublicSingleton)]
-        public static bool Critical(object self, bool value) {
+        public static void Critical(RubyContext/*!*/ context, object self, bool value) {
             RubyThreadInfo.RegisterThread(Thread.CurrentThread);
-            return false;
+            if (value) {
+                Monitor.Enter(context.CriticalMonitor);
+                context.IsInCriticalRegion = true;
+            } else {
+                context.IsInCriticalRegion = false;
+                Monitor.Exit(context.CriticalMonitor);
+            }
         }
 
         [RubyMethod("current", RubyMethodAttributes.PublicSingleton)]
@@ -665,7 +668,14 @@
         }
 
         [RubyMethod("stop", RubyMethodAttributes.PublicSingleton)]
-        public static void Stop(object self) {
+        public static void Stop(RubyContext/*!*/ context, object self) {
+            if (context.IsInCriticalRegion) {
+                Critical(context, self, false);
+            }
+            DoSleep();
+        }
+
+        internal static void DoSleep() {
             RubyThreadInfo.RegisterThread(Thread.CurrentThread);
             // TODO: MRI throws an exception if you try to stop the main thread
             RubyThreadInfo info = RubyThreadInfo.FromThread(Thread.CurrentThread);
===================================================================
edit: $/Dev10/feature/vs_langs01/Merlin/Main/Languages/Ruby/Ruby/Runtime/RubyContext.cs;C691193
File: RubyContext.cs
===================================================================
--- $/Dev10/feature/vs_langs01/Merlin/Main/Languages/Ruby/Ruby/Runtime/RubyContext.cs;C691193  (server)    1/5/2009 2:02 PM
+++ Shelved Change: $/Dev10/feature/vs_langs01/Merlin/Main/Languages/Ruby/Ruby/Runtime/RubyContext.cs;critical
@@ -117,6 +117,8 @@
         private readonly RubyInputProvider/*!*/ _inputProvider;
         private readonly Dictionary<string/*!*/, GlobalVariable>/*!*/ _globalVariables;
         private Proc _traceListener;
+        private readonly object _criticalMonitor = new object();
+        private bool _isInCriticalRegion;
 
         [ThreadStatic]
         private bool _traceListenerSuspended;
@@ -288,6 +290,15 @@
             set { _itemSeparator = value; }
         }
 
+        public object CriticalMonitor {
+            get { return _criticalMonitor; }
+        }
+
+        public bool IsInCriticalRegion {
+            get { return _isInCriticalRegion; }
+            set { _isInCriticalRegion = value; }
+        }
+
         public Proc TraceListener {
             get { return _traceListener; }
             set { _traceListener = value; }
===================================================================