diff --git a/moo/configure b/moo/configure
index 37e6f08..85d27a1 100755
--- a/moo/configure
+++ b/moo/configure
@@ -18566,8 +18566,8 @@ esac
 LIBM=$LIBM
 
 
-{ $as_echo "$as_me:${as_lineno-$LINENO}: checking __builtin_memset" >&5
-$as_echo_n "checking __builtin_memset... " >&6; }
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for __builtin_memset" >&5
+$as_echo_n "checking for __builtin_memset... " >&6; }
 cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
@@ -18592,8 +18592,8 @@ $as_echo "no" >&6; }
 fi
 rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
 
-{ $as_echo "$as_me:${as_lineno-$LINENO}: checking __builtin_memcpy" >&5
-$as_echo_n "checking __builtin_memcpy... " >&6; }
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for __builtin_memcpy" >&5
+$as_echo_n "checking for __builtin_memcpy... " >&6; }
 cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
@@ -18618,8 +18618,8 @@ $as_echo "no" >&6; }
 fi
 rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
 
-{ $as_echo "$as_me:${as_lineno-$LINENO}: checking __builtin_memmove" >&5
-$as_echo_n "checking __builtin_memmove... " >&6; }
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for __builtin_memmove" >&5
+$as_echo_n "checking for __builtin_memmove... " >&6; }
 cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
@@ -18644,8 +18644,8 @@ $as_echo "no" >&6; }
 fi
 rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
 
-{ $as_echo "$as_me:${as_lineno-$LINENO}: checking __builtin_memcmp" >&5
-$as_echo_n "checking __builtin_memcmp... " >&6; }
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for __builtin_memcmp" >&5
+$as_echo_n "checking for __builtin_memcmp... " >&6; }
 cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
@@ -18670,6 +18670,32 @@ $as_echo "no" >&6; }
 fi
 rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
 
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking computed goto usability" >&5
+$as_echo_n "checking computed goto usability... " >&6; }
+cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+int
+main ()
+{
+void *jp = &&jpt; goto *jp; 1; jpt: 2;
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_c_try_compile "$LINENO"; then :
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: yes" >&5
+$as_echo "yes" >&6; }
+
+$as_echo "#define HAVE_COMPUTED_GOTO 1" >>confdefs.h
+
+else
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
+$as_echo "no" >&6; }
+
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking for ANSI C header files" >&5
 $as_echo_n "checking for ANSI C header files... " >&6; }
 if ${ac_cv_header_stdc+:} false; then :
diff --git a/moo/configure.ac b/moo/configure.ac
index 0101258..e35b1cf 100644
--- a/moo/configure.ac
+++ b/moo/configure.ac
@@ -108,7 +108,7 @@ LT_LIB_M
 AC_SUBST(LIBM, $LIBM)
 
 dnl check some compiler builtins
-AC_MSG_CHECKING([__builtin_memset])
+AC_MSG_CHECKING([for __builtin_memset])
 AC_COMPILE_IFELSE(
 	[AC_LANG_PROGRAM([], [__builtin_memset ((void*)1, ' ', 10);])],
 	[AC_MSG_RESULT(yes)
@@ -116,7 +116,7 @@ AC_COMPILE_IFELSE(
 	[AC_MSG_RESULT(no)]
 )
 
-AC_MSG_CHECKING([__builtin_memcpy])
+AC_MSG_CHECKING([for __builtin_memcpy])
 AC_COMPILE_IFELSE(
 	[AC_LANG_PROGRAM([], [__builtin_memcpy ((void*)1, (void*)2, 10);])],
 	[AC_MSG_RESULT(yes)
@@ -124,7 +124,7 @@ AC_COMPILE_IFELSE(
 	[AC_MSG_RESULT(no)]
 )
 
-AC_MSG_CHECKING([__builtin_memmove])
+AC_MSG_CHECKING([for __builtin_memmove])
 AC_COMPILE_IFELSE(
 	[AC_LANG_PROGRAM([], [__builtin_memmove ((void*)1, (void*)2, 10);])],
 	[AC_MSG_RESULT(yes)
@@ -132,7 +132,7 @@ AC_COMPILE_IFELSE(
 	[AC_MSG_RESULT(no)]
 )
 
-AC_MSG_CHECKING([__builtin_memcmp])
+AC_MSG_CHECKING([for __builtin_memcmp])
 AC_COMPILE_IFELSE(
 	[AC_LANG_PROGRAM([], [int a = __builtin_memcmp ((void*)1, (void*)2, 10);])],
 	[AC_MSG_RESULT(yes)
@@ -140,6 +140,14 @@ AC_COMPILE_IFELSE(
 	[AC_MSG_RESULT(no)]
 )
 
+AC_MSG_CHECKING([computed goto usability])
+AC_COMPILE_IFELSE(
+	[AC_LANG_PROGRAM( [], [[void *jp = &&jpt; goto *jp; 1; jpt: 2; ]])],
+	[AC_MSG_RESULT(yes)
+	 AC_DEFINE(HAVE_COMPUTED_GOTO, 1, [computed gotos])],
+	[AC_MSG_RESULT(no)]
+)
+
 dnl check header files.
 AC_HEADER_STDC
 AC_CHECK_HEADERS([stddef.h wchar.h wctype.h errno.h signal.h fcntl.h dirent.h])
diff --git a/moo/kernel/Mill.moo b/moo/kernel/Mill.moo
index 37903b8..d561363 100644
--- a/moo/kernel/Mill.moo
+++ b/moo/kernel/Mill.moo
@@ -329,6 +329,23 @@ class MyObject(Object)
 		
 		Processor sleepFor: 20.
 	}
+	
+	(*
+	#method(#class) main
+	{
+		| event |
+		
+		Timer fire: [ 'Timer job' dump. ] in: 3000.
+		
+		GUI on: #XXX do: [:evt | ... ].
+		GUI on: #YYYY do: [:evt | ... ].
+
+		while (true)
+		{
+			event := GUI waitForEvent.
+			GUI dispatchEvent: event.
+		}
+	}*)
 }
 
 (*
diff --git a/moo/lib/exec.c b/moo/lib/exec.c
index dff140e..90143c9 100644
--- a/moo/lib/exec.c
+++ b/moo/lib/exec.c
@@ -2914,6 +2914,106 @@ static int send_private_message (moo_t* moo, const moo_ooch_t* nameptr, moo_oow_
 }
 /* ------------------------------------------------------------------------- */
 
+static MOO_INLINE int switch_process_if_needed (moo_t* moo)
+{
+	if (moo->sem_heap_count > 0)
+	{
+		moo_ntime_t ft, now;
+		vm_gettime (moo, &now);
+
+		do
+		{
+			MOO_ASSERT (moo, MOO_OOP_IS_SMOOI(moo->sem_heap[0]->heap_ftime_sec));
+			MOO_ASSERT (moo, MOO_OOP_IS_SMOOI(moo->sem_heap[0]->heap_ftime_nsec));
+
+			MOO_INITNTIME (&ft,
+				MOO_OOP_TO_SMOOI(moo->sem_heap[0]->heap_ftime_sec),
+				MOO_OOP_TO_SMOOI(moo->sem_heap[0]->heap_ftime_nsec)
+			);
+
+			if (MOO_CMPNTIME(&ft, (moo_ntime_t*)&now) <= 0)
+			{
+				moo_oop_process_t proc;
+
+				/* waited long enough. signal the semaphore */
+
+				proc = signal_semaphore (moo, moo->sem_heap[0]);
+				/* [NOTE] no moo_pushtmp() on proc. no GC must occur
+				 *        in the following line until it's used for
+				 *        wake_new_process() below. */
+				delete_from_sem_heap (moo, 0);
+
+				/* if no process is waiting on the semaphore, 
+				 * signal_semaphore() returns moo->_nil. */
+
+				if (moo->processor->active == moo->nil_process && (moo_oop_t)proc != moo->_nil)
+				{
+					/* this is the only runnable process. 
+					 * switch the process to the running state.
+					 * it uses wake_new_process() instead of
+					 * switch_to_process() as there is no running 
+					 * process at this moment */
+					MOO_ASSERT (moo, proc->state == MOO_SMOOI_TO_OOP(PROC_STATE_RUNNABLE));
+					MOO_ASSERT (moo, proc == moo->processor->runnable_head);
+
+					wake_new_process (moo, proc);
+					moo->proc_switched = 1;
+				}
+			}
+			else if (moo->processor->active == moo->nil_process)
+			{
+				MOO_SUBNTIME (&ft, &ft, (moo_ntime_t*)&now);
+				vm_sleep (moo, &ft); /* TODO: change this to i/o multiplexer??? */
+				vm_gettime (moo, &now);
+			}
+			else 
+			{
+				break;
+			}
+		} 
+		while (moo->sem_heap_count > 0);
+	}
+
+	if (moo->processor->active == moo->nil_process) 
+	{
+		/* no more waiting semaphore and no more process */
+		MOO_ASSERT (moo, moo->processor->tally = MOO_SMOOI_TO_OOP(0));
+		MOO_LOG0 (moo, MOO_LOG_IC | MOO_LOG_DEBUG, "No more runnable process\n");
+
+		#if 0
+		if (there is semaphore awaited.... )
+		{
+		/* DO SOMETHING */
+		}
+		#endif
+
+		return 0;
+	}
+
+	while (moo->sem_list_count > 0)
+	{
+		/* handle async signals */
+		--moo->sem_list_count;
+		signal_semaphore (moo, moo->sem_list[moo->sem_list_count]);
+	}
+	/*
+	if (semaphore heap has pending request)
+	{
+		signal them...
+	}*/
+
+	/* TODO: implement different process switching scheme - time-slice or clock based??? */
+#if defined(MOO_EXTERNAL_PROCESS_SWITCH)
+	if (!moo->proc_switched && moo->switch_proc) { switch_to_next_runnable_process (moo); }
+	moo->switch_proc = 0;
+#else
+	if (!moo->proc_switched) { switch_to_next_runnable_process (moo); }
+#endif
+
+	moo->proc_switched = 0;
+	return 1;
+}
+
 int moo_execute (moo_t* moo)
 {
 	moo_oob_t bcode;
@@ -2922,6 +3022,7 @@ int moo_execute (moo_t* moo)
 	int unwind_protect;
 	moo_oop_context_t unwind_start;
 	moo_oop_context_t unwind_stop;
+	int vm_startup_called = 0;
 
 #if defined(MOO_PROFILE_VM)
 	moo_uintmax_t inst_counter = 0;
@@ -2934,105 +3035,12 @@ int moo_execute (moo_t* moo)
 	MOO_ASSERT (moo, moo->active_context != MOO_NULL);
 
 	vm_startup (moo);
+	vm_startup_called = 1;
 	moo->proc_switched = 0;
 
 	while (1)
 	{
-		if (moo->sem_heap_count > 0)
-		{
-			moo_ntime_t ft, now;
-			vm_gettime (moo, &now);
-
-			do
-			{
-				MOO_ASSERT (moo, MOO_OOP_IS_SMOOI(moo->sem_heap[0]->heap_ftime_sec));
-				MOO_ASSERT (moo, MOO_OOP_IS_SMOOI(moo->sem_heap[0]->heap_ftime_nsec));
-
-				MOO_INITNTIME (&ft,
-					MOO_OOP_TO_SMOOI(moo->sem_heap[0]->heap_ftime_sec),
-					MOO_OOP_TO_SMOOI(moo->sem_heap[0]->heap_ftime_nsec)
-				);
-
-				if (MOO_CMPNTIME(&ft, (moo_ntime_t*)&now) <= 0)
-				{
-					moo_oop_process_t proc;
-
-					/* waited long enough. signal the semaphore */
-
-					proc = signal_semaphore (moo, moo->sem_heap[0]);
-					/* [NOTE] no moo_pushtmp() on proc. no GC must occur
-					 *        in the following line until it's used for
-					 *        wake_new_process() below. */
-					delete_from_sem_heap (moo, 0);
-
-					/* if no process is waiting on the semaphore, 
-					 * signal_semaphore() returns moo->_nil. */
-
-					if (moo->processor->active == moo->nil_process && (moo_oop_t)proc != moo->_nil)
-					{
-						/* this is the only runnable process. 
-						 * switch the process to the running state.
-						 * it uses wake_new_process() instead of
-						 * switch_to_process() as there is no running 
-						 * process at this moment */
-						MOO_ASSERT (moo, proc->state == MOO_SMOOI_TO_OOP(PROC_STATE_RUNNABLE));
-						MOO_ASSERT (moo, proc == moo->processor->runnable_head);
-
-						wake_new_process (moo, proc);
-						moo->proc_switched = 1;
-					}
-				}
-				else if (moo->processor->active == moo->nil_process)
-				{
-					MOO_SUBNTIME (&ft, &ft, (moo_ntime_t*)&now);
-					vm_sleep (moo, &ft); /* TODO: change this to i/o multiplexer??? */
-					vm_gettime (moo, &now);
-				}
-				else 
-				{
-					break;
-				}
-			} 
-			while (moo->sem_heap_count > 0);
-		}
-
-		if (moo->processor->active == moo->nil_process) 
-		{
-			/* no more waiting semaphore and no more process */
-			MOO_ASSERT (moo, moo->processor->tally = MOO_SMOOI_TO_OOP(0));
-			MOO_LOG0 (moo, MOO_LOG_IC | MOO_LOG_DEBUG, "No more runnable process\n");
-
-			#if 0
-			if (there is semaphore awaited.... )
-			{
-			/* DO SOMETHING */
-			}
-			#endif
-
-			break;
-		}
-
-		while (moo->sem_list_count > 0)
-		{
-			/* handle async signals */
-			--moo->sem_list_count;
-			signal_semaphore (moo, moo->sem_list[moo->sem_list_count]);
-		}
-		/*
-		if (semaphore heap has pending request)
-		{
-			signal them...
-		}*/
-
-		/* TODO: implement different process switching scheme - time-slice or clock based??? */
-#if defined(MOO_EXTERNAL_PROCESS_SWITCH)
-		if (!moo->proc_switched && moo->switch_proc) { switch_to_next_runnable_process (moo); }
-		moo->switch_proc = 0;
-#else
-		if (!moo->proc_switched) { switch_to_next_runnable_process (moo); }
-#endif
-
-		moo->proc_switched = 0;
+		if (switch_process_if_needed(moo) == 0) break; /* no more runnable process */
 
 #if defined(MOO_DEBUG_VM_EXEC)
 		fetched_instruction_pointer = moo->ip;
@@ -3804,7 +3812,7 @@ int moo_execute (moo_t* moo)
 				 */
 				moo->ip--; 
 			#else
-				if (moo->active_context->origin == moo->processor->active->initial_context->origin)
+				if (MOO_UNLIKELY(moo->active_context->origin == moo->processor->active->initial_context->origin))
 				{
 					/* method return from a processified block
 					 * 
@@ -4141,7 +4149,6 @@ int moo_execute (moo_t* moo)
 				LOG_INST_0 (moo, "noop");
 				break;
 
-
 			default:
 				MOO_LOG1 (moo, MOO_LOG_IC | MOO_LOG_FATAL, "Fatal error - unknown byte code 0x%zx\n", bcode);
 				moo->errnum = MOO_EINTERN;
@@ -4158,7 +4165,7 @@ done:
 	return 0;
 
 oops:
-	/* TODO: anything to do here? */
+	if (vm_startup_called) vm_cleanup (moo);
 	return -1;
 }
 
@@ -4182,3 +4189,14 @@ int moo_invoke (moo_t* moo, const moo_oocs_t* objname, const moo_oocs_t* mthname
 	return n;
 }
 
+#if 0
+int moo_invoke (moo_t* moo, const moo_oocs_t* objname, const moo_oocs_t* mthname)
+{
+/* TODO: .... */
+	/* call 
+	 * 	System initializeClasses
+	 * and invoke 
+	 *   objname mthname
+	 */
+}
+#endif
diff --git a/moo/lib/main.c b/moo/lib/main.c
index a2adf4a..a3b6187 100644
--- a/moo/lib/main.c
+++ b/moo/lib/main.c
@@ -116,6 +116,9 @@ typedef struct xtn_t xtn_t;
 struct xtn_t
 {
 	const char* source_path; /* main source file */
+#if defined(_WIN32)
+	HANDLE waitable_timer;
+#endif
 };
 
 /* ========================================================================= */
@@ -675,7 +678,8 @@ static void vm_gettime (moo_t* moo, moo_ntime_t* now)
 static void vm_sleep (moo_t* moo, const moo_ntime_t* dur)
 {
 #if defined(_WIN32)
-	if (moo->waitable_timer)
+	xtn_t* xtn = moo_getxtn(moo);
+	if (xtn->waitable_timer)
 	{
 		LARGE_INTEGER li;
 		li.QuadPart = -MOO_SECNSEC_TO_NSEC(dur->sec, dur->nsec);
@@ -735,17 +739,19 @@ static void vm_sleep (moo_t* moo, const moo_ntime_t* dur)
 static void vm_startup (moo_t* moo)
 {
 #if defined(_WIN32)
-	moo->waitable_timer = CreateWaitableTimer(MOO_NULL, TRUE, MOO_NULL);
+	xtn_t* xtn = (xtn_t*)moo_getxtn(moo);
+	xtn->waitable_timer = CreateWaitableTimer(MOO_NULL, TRUE, MOO_NULL);
 #endif
 }
 
 static void vm_cleanup (moo_t* moo)
 {
 #if defined(_WIN32)
-	if (moo->waitable_timer)
+	xtn_t* xtn = (xtn_t*)moo_getxtn(moo);
+	if (xtn->waitable_timer)
 	{
-		CloseHandle (moo->waitable_timer);
-		moo->waitable_timer = MOO_NULL;
+		CloseHandle (xtn->waitable_timer);
+		xtn->waitable_timer = MOO_NULL;
 	}
 #endif
 }
diff --git a/moo/lib/moo-cfg.h.in b/moo/lib/moo-cfg.h.in
index 68778bb..533ebe5 100644
--- a/moo/lib/moo-cfg.h.in
+++ b/moo/lib/moo-cfg.h.in
@@ -57,6 +57,9 @@
 /* Define to 1 if you have the `closedir' function. */
 #undef HAVE_CLOSEDIR
 
+/* computed gotos */
+#undef HAVE_COMPUTED_GOTO
+
 /* Define to 1 if you have the `coshq' function. */
 #undef HAVE_COSHQ
 
diff --git a/moo/lib/moo-cmn.h b/moo/lib/moo-cmn.h
index ac2c433..af9bcba 100644
--- a/moo/lib/moo-cmn.h
+++ b/moo/lib/moo-cmn.h
@@ -720,11 +720,12 @@ typedef struct moo_t moo_t;
 #endif
 
 #if defined(MOO_HAVE_BUILTIN_EXPECT)
-#	define MOO_LIKELY(x) (__builtin_expect(!!x,1))
-#	define MOO_UNLIKELY(x) (__builtin_expect(!!x,0))
+#	define MOO_LIKELY(x) (__builtin_expect(!!(x),1))
+#	define MOO_UNLIKELY(x) (__builtin_expect(!!(x),0))
 #else
 #	define MOO_LIKELY(x) (x)
 #	define MOO_UNLIKELY(x) (x)
 #endif
 
+
 #endif
diff --git a/moo/lib/moo-prv.h b/moo/lib/moo-prv.h
index b64e607..43114c6 100644
--- a/moo/lib/moo-prv.h
+++ b/moo/lib/moo-prv.h
@@ -873,17 +873,17 @@ enum moo_bcode_t
 
 	/* -------------------------------------- */
 
-	BCODE_MAKE_ARRAY               = 0xF5, /* 245 */
-	BCODE_POP_INTO_ARRAY           = 0xF6, /* 246 */
-	BCODE_DUP_STACKTOP             = 0xF7,
-	BCODE_POP_STACKTOP             = 0xF8,
-	BCODE_RETURN_STACKTOP          = 0xF9, /* ^something */
-	BCODE_RETURN_RECEIVER          = 0xFA, /* ^self */
-	BCODE_RETURN_FROM_BLOCK        = 0xFB, /* return the stack top from a block */
-	BCODE_LOCAL_RETURN             = 0xFC,
-	BCODE_MAKE_BLOCK               = 0xFD,
-	BCODE_SEND_BLOCK_COPY          = 0xFE,
-	BCODE_NOOP                     = 0xFF
+	BCODE_MAKE_ARRAY                 = 0xF5, /* 245 */
+	BCODE_POP_INTO_ARRAY             = 0xF6, /* 246 */
+	BCODE_DUP_STACKTOP               = 0xF7,
+	BCODE_POP_STACKTOP               = 0xF8,
+	BCODE_RETURN_STACKTOP            = 0xF9, /* ^something */
+	BCODE_RETURN_RECEIVER            = 0xFA, /* ^self */
+	BCODE_RETURN_FROM_BLOCK          = 0xFB, /* return the stack top from a block */
+	BCODE_LOCAL_RETURN               = 0xFC,
+	BCODE_MAKE_BLOCK                 = 0xFD,
+	BCODE_SEND_BLOCK_COPY            = 0xFE,
+	BCODE_NOOP                       = 0xFF
 };
 
 #if defined(__cplusplus)
@@ -1181,7 +1181,7 @@ moo_oop_t moo_strtoint (
 moo_oop_t moo_inttostr (
 	moo_t*      moo,
 	moo_oop_t   num,
-	int          radix
+	int         radix
 );
 
 /* ========================================================================= */