+=head1 Hook manipulation
+*/
+
+#ifdef USE_ITHREADS
+# define OP_CHECK_MUTEX_INIT MUTEX_INIT(&PL_check_mutex)
+# define OP_CHECK_MUTEX_LOCK MUTEX_LOCK(&PL_check_mutex)
+# define OP_CHECK_MUTEX_UNLOCK MUTEX_UNLOCK(&PL_check_mutex)
+# define OP_CHECK_MUTEX_TERM MUTEX_DESTROY(&PL_check_mutex)
+#else
+# define OP_CHECK_MUTEX_INIT NOOP
+# define OP_CHECK_MUTEX_LOCK NOOP
+# define OP_CHECK_MUTEX_UNLOCK NOOP
+# define OP_CHECK_MUTEX_TERM NOOP
+#endif
+
+/*