+#ifdef FEATURE_EXTERNAL_FILTERS
+extern privoxy_mutex_t external_filter_mutex;
+#endif
+
+#ifdef FEATURE_CLIENT_TAGS
+extern privoxy_mutex_t client_tags_mutex;
+#endif
+
+#ifdef FEATURE_EXTENDED_STATISTICS
+extern privoxy_mutex_t filter_statistics_mutex;
+extern privoxy_mutex_t block_statistics_mutex;
+#endif
+