diff --git a/src/lib/plugin.c b/src/lib/plugin.c
index 18c4b7630..364dc3b7a 100644
--- a/src/lib/plugin.c
+++ b/src/lib/plugin.c
@@ -5,16 +5,42 @@
 
 #include "plugin.h"
 
+/* TODO should be set by the build system to the actual plugin path */
+#define CINELERRA_PLUGIN_PATH "~/.cinelerra3/plugins:/usr/local/lib/cinelerra3/plugins"
+
+/* recognized extensions */
+#define CINELERRA_PLUGIN_EXT "plugin:so"
+
+/*
+  For future:
+  #define CINELERRA_PLUGIN_EXT "plugin:so:cplugin:c"
+  imagine using C source plugins compiled with libtcc on the fly
+*/
+
 NOBUG_DEFINE_FLAG (cinelerra_plugin);
 
+/* errors */
+const char* CINELERRA_PLUGIN_SUCCESS = NULL;
+const char* CINELERRA_PLUGIN_EALLOC = "Memory allocation failure";
+const char* CINELERRA_PLUGIN_ENFOUND = "No such plugin";
+const char* CINELERRA_PLUGIN_ENIFACE = "No such interface";
+const char* CINELERRA_PLUGIN_EREVISION = "Interface revision too old";
 
 struct cinelerra_plugin
 {
-  const char* name; /*TODO store full and short name, sort by shortname?*/
+  /* short name as queried ("effects/audio/normalize") used for sorting/finding */
+  const char* name;
+
+  /* long names as looked up ("/usr/local/lib/cinelerra3/plugins/effects/audio/normalize.so") */
+  const char* pathname;
+
+  /* pointer to the extension part of 'pathname' */
+  const char* ext;
 
   /* use count for all interfaces of this plugin */
   unsigned use_count;
 
+  /* time when the last open or close action happened */
   time_t last;
 
   /* dlopen handle */
@@ -24,28 +50,62 @@ struct cinelerra_plugin
 /* global plugin registry */
 void* cinelerra_plugin_registry = NULL;
 
+/* plugin operations are protected by one big mutex */
+pthread_mutex_t cinelerra_plugin_mutex = PTHREAD_MUTEX_INITIALIZER;
 
+/* Thread local storage, for now only the error state */
+static pthread_key_t cinelerra_plugin_tls_error;
+static pthread_once_t cinelerra_plugin_initialized = PTHREAD_ONCE_INIT;
+
+void
+cinelerra_plugin_tls_init (void)
+{
+  pthread_key_create (&cinelerra_plugin_tls_error, NULL);
+}
+
+/* the compare function for the registry tree */
 static int
-cmp_plugin_name (const void* a, const void* b)
+cinelerra_plugin_name_cmp (const void* a, const void* b)
 {
   return strcmp (((struct cinelerra_plugin*) a)->name, ((struct cinelerra_plugin*) b)->name);
 }
 
+const char*
+cinelerra_plugin_lookup (struct cinelerra_plugin* self, const char* name, const char* path, const char* ext)
+{
+  /*for each in path*/
+  /*for each extension*/
+  /*try to find name*/
+
+}
+
 struct cinelerra_interface*
 cinelerra_interface_open (const char* name, const char* interface, size_t min_revision)
 {
   REQUIRE (min_revision > sizeof(cinelerra_interface), "try to use an empty interface eh?");
-  REQUIRE (interface, "interface name must be defined");
+  REQUIRE (interface, "interface name must be given");
+
+  pthread_mutex_lock (&cinelerra_plugin_mutex);
+
+  pthread_once (&cinelerra_plugin_initialized, cinelerra_plugin_tls_init);
 
   struct cinelerra_plugin plugin;
   struct cinelerra_plugin** found;
 
-  // TODO cook somewhere (pluginpath+name+.so)
+  // if (name) (NULL means main app)
+
+  /*lookup for $CINELERRA_PLUGIN_PATH*/
+
+  /* else lookup for -DCINELERRA_PLUGIN_PATH */
+#ifdef CINELERRA_PLUGIN_PATH
+#endif
+  /* else fail */
+
   plugin.name = name;
 
-  found = tsearch (&plugin, &cinelerra_plugin_registry, cmp_plugin_name);
+  found = tsearch (&plugin, &cinelerra_plugin_registry, cinelerra_plugin_name_cmp);
   if (!found)
-    return NULL;
+    goto ealloc0;
 
   if (*found == &plugin)
     {
@@ -107,6 +167,7 @@ cinelerra_interface_open (const char* name, const char* interface, size_t min_re
   (*found)->use_count++;
   ret->use_count++;
 
+  pthread_mutex_unlock (&cinelerra_plugin_mutex);
   return ret;
 
   /* Error cleanup */
@@ -121,7 +182,9 @@ cinelerra_interface_open (const char* name, const char* interface, size_t min_re
   free (*found);
  ealloc1:
   *found = &plugin;
-  tdelete (&plugin, &cinelerra_plugin_registry, cmp_plugin_name);
+  tdelete (&plugin, &cinelerra_plugin_registry, cinelerra_plugin_name_cmp);
+ ealloc0:
+  pthread_mutex_lock (&cinelerra_plugin_mutex);
   return NULL;
 }
 
@@ -131,6 +194,8 @@ cinelerra_interface_close (struct cinelerra_interface* self)
   if(!self)
     return;
 
+  pthread_mutex_lock (&cinelerra_plugin_mutex);
+
   struct cinelerra_plugin* plugin = self->plugin;
   
   plugin->use_count--;
@@ -151,9 +216,10 @@ cinelerra_interface_close (struct cinelerra_interface* self)
         destroy();
 
       /* and now cleanup */
-      tdelete (plugin, &cinelerra_plugin_registry, cmp_plugin_name);
+      tdelete (plugin, &cinelerra_plugin_registry, cinelerra_plugin_name_cmp);
       free ((char*)plugin->name);
       dlclose(plugin->handle);
       free (plugin);
     }
+  pthread_mutex_unlock (&cinelerra_plugin_mutex);
 }
diff --git a/src/lib/plugin.h b/src/lib/plugin.h
index 409d954e9..573d4a6ca 100644
--- a/src/lib/plugin.h
+++ b/src/lib/plugin.h
@@ -119,6 +119,10 @@ cinelerra_plugin_expire (time_t age);
 const char*
 cinelerra_plugin_error ();
 
+/// success, NULL
+extern const char* CINELERRA_PLUGIN_SUCCESS;
+/// memory allocation error
+extern const char* CINELERRA_PLUGIN_EALLOC;
 /// Plugin not found
 extern const char* CINELERRA_PLUGIN_ENFOUND;
 /// no such interface