diff --git a/hawk/lib/cli-imp.h b/hawk/lib/cli-imp.h
index bf7188b4..8e63fc8d 100644
--- a/hawk/lib/cli-imp.h
+++ b/hawk/lib/cli-imp.h
@@ -1,7 +1,7 @@
 /*
  * $Id$
  *
-    Copyright (c) 2014-2019 Chung, Hyung-Hwan. All rights reserved.
+    Copyright (c) 2006-2020 Chung, Hyung-Hwan. All rights reserved.
 
     Redistribution and use in source and binary forms, with or without
     modification, are permitted provided that the following conditions
diff --git a/hawk/lib/cli.c b/hawk/lib/cli.c
index ab603cb5..43c2a56e 100644
--- a/hawk/lib/cli.c
+++ b/hawk/lib/cli.c
@@ -1,7 +1,7 @@
 /*
  * $Id$
  *
-    Copyright (c) 2014-2019 Chung, Hyung-Hwan. All rights reserved.
+    Copyright (c) 2006-2020 Chung, Hyung-Hwan. All rights reserved.
 
     Redistribution and use in source and binary forms, with or without
     modification, are permitted provided that the following conditions
diff --git a/hawk/lib/fmt.c b/hawk/lib/fmt.c
index bbac54dc..adba322a 100644
--- a/hawk/lib/fmt.c
+++ b/hawk/lib/fmt.c
@@ -1,7 +1,7 @@
 /*
  * $Id$
  *
-    Copyright (c) 2014-2019 Chung, Hyung-Hwan. All rights reserved.
+    Copyright (c) 2006-2020 Chung, Hyung-Hwan. All rights reserved.
 
     Redistribution and use in source and binary forms, with or without
     modification, are permitted provided that the following conditions
diff --git a/hawk/lib/hawk-cli.h b/hawk/lib/hawk-cli.h
index 53bdf41e..2d4b5dfc 100644
--- a/hawk/lib/hawk-cli.h
+++ b/hawk/lib/hawk-cli.h
@@ -1,7 +1,7 @@
 /*
  * $Id$
  *
-    Copyright (c) 2014-2019 Chung, Hyung-Hwan. All rights reserved.
+    Copyright (c) 2006-2020 Chung, Hyung-Hwan. All rights reserved.
 
     Redistribution and use in source and binary forms, with or without
     modification, are permitted provided that the following conditions
diff --git a/hawk/lib/mod-hawk.c b/hawk/lib/mod-hawk.c
index 4decd0cd..f69e7307 100644
--- a/hawk/lib/mod-hawk.c
+++ b/hawk/lib/mod-hawk.c
@@ -26,7 +26,14 @@
 
 #include "mod-hawk.h"
 #include "hawk-prv.h"
+#include <hawk-mtx.h>
 
+
+struct mod_data_t
+{
+	hawk_mtx_t mq_mtx;
+};
+typedef struct mod_data_t mod_data_t;
 /* ----------------------------------------------------------------- */
 
 /*
@@ -150,7 +157,14 @@ static int fnc_function_exists (hawk_rtx_t* rtx, const hawk_fnc_info_t* fi)
 			if (!rx)
 			{
 				hawk_mod_sym_t sym;
+				mod_data_t* md;
+
+				md = (mod_data_t*)fi->mod->ctx;
+				/* hawk_query_module_with_name() may update some shared data under
+				 * the hawk object. use a mutex for shared data safety */
+				hawk_mtx_lock (&md->mq_mtx, HAWK_NULL);
 				rx = (hawk_query_module_with_name(hawk_rtx_gethawk(rtx), &name, &sym) != HAWK_NULL);
+				hawk_mtx_unlock (&md->mq_mtx);
 			}
 		}
 		hawk_rtx_freevaloocstr (rtx, a0, name.ptr);
@@ -449,17 +463,27 @@ static void fini (hawk_mod_t* mod, hawk_rtx_t* rtx)
 
 static void unload (hawk_mod_t* mod, hawk_t* hawk)
 {
-	/* nothing to do */
+	mod_data_t* md = (mod_data_t*)mod->ctx;
+
+	hawk_mtx_fini (&md->mq_mtx);
+	hawk_freemem (hawk, md);
 }
 
 int hawk_mod_hawk (hawk_mod_t* mod, hawk_t* hawk)
 {
+	mod_data_t* md;
+
+	md = hawk_allocmem(hawk, HAWK_SIZEOF(*md));
+	if (HAWK_UNLIKELY(!md)) return -1;
+
+	hawk_mtx_init (&md->mq_mtx, hawk_getgem(hawk));
+
 	mod->query = query;
 	mod->unload = unload;
 
 	mod->init = init;
 	mod->fini = fini;
-	mod->ctx = HAWK_NULL;
+	mod->ctx = md;
 
 	return 0;
 }
diff --git a/hawk/lib/std.c b/hawk/lib/std.c
index 1d4e3918..ebe2b4ee 100644
--- a/hawk/lib/std.c
+++ b/hawk/lib/std.c
@@ -363,7 +363,7 @@ void* hawk_stdmodopen (hawk_t* hawk, const hawk_mod_spec_t* spec)
 	else
 	{
 		void* h;
-		h = lt_dlopen(NULL);
+		h = lt_dlopen(HAWK_NULL);
 		if (HAWK_UNLIKELY(!h)) hawk_seterrfmt (hawk, HAWK_NULL, HAWK_ESYSERR, HAWK_T("%hs"), lt_dlerror());
 		return h;
 	}
@@ -409,7 +409,7 @@ void* hawk_stdmodopen (hawk_t* hawk, const hawk_mod_spec_t* spec)
 	else
 	{
 		HMODULE h;
-		h = GetModuleHandle(NULL);
+		h = GetModuleHandle(HAWK_NULL);
 		if (!h) hawk_seterrnum (hawk, HAWK_NULL, hawk_syserr_to_errnum(GetLastError());
 		return h;
 	}
@@ -512,7 +512,7 @@ void* hawk_stdmodopen (hawk_t* hawk, const hawk_mod_spec_t* spec)
 	else
 	{
 		void* h;
-		h = GetModuleHandle(NULL);
+		h = GetModuleHandle(HAWK_NULL);
 		if (!h) hawk_seterrnum (hawk, HAWK_NULL, HAWK_ESYSERR);
 		return h;
 	}
@@ -572,11 +572,11 @@ void hawk_stdmodclose (hawk_t* hawk, void* handle)
 #if defined(USE_LTDL)
 	lt_dlclose (handle);
 #elif defined(_WIN32)
-	if (handle != GetModuleHandle(NULL)) FreeLibrary ((HMODULE)handle);
+	if (handle != GetModuleHandle(HAWK_NULL)) FreeLibrary ((HMODULE)handle);
 #elif defined(__OS2__)
 	DosFreeModule ((HMODULE)handle);
 #elif defined(__DOS__) && defined(HAWK_ENABLE_DOS_DYNAMIC_MODULE)
-	if (handle != GetModuleHandle(NULL))  FreeModule (handle);
+	if (handle != GetModuleHandle(HAWK_NULL))  FreeModule (handle);
 #elif defined(USE_DLFCN)
 	dlclose (handle);
 #else