[libpeas] Document that the lua5.1 plugin loader is not thread-safe

[Garrett Regier <gregier src gnome org>]

commit b4664d44f991fd86e5c08627df6120c49dba1245
Author: Garrett Regier <garrett regier riftio com>
Date:   Sat Nov 8 11:14:15 2014 -0800

    Document that the lua5.1 plugin loader is not thread-safe
    
    https://bugzilla.gnome.org/show_bug.cgi?id=739619

 libpeas/peas-engine.c                   |    4 ++++
 loaders/lua5.1/peas-plugin-loader-lua.c |    4 ++++
 2 files changed, 8 insertions(+), 0 deletions(-)
---
diff --git a/libpeas/peas-engine.c b/libpeas/peas-engine.c
index c6b7043..92cf055 100644
--- a/libpeas/peas-engine.c
+++ b/libpeas/peas-engine.c
@@ -685,6 +685,10 @@ get_plugin_loader (PeasEngine *engine,
  * peas_engine_enable_loader (engine, "python");
  * ]|
  *
+ * Unlike the C, python and python3 plugin loaders the lua5.1 plugin
+ * loader can only be used from a single thread. Should this happen
+ * a deadlock will occur.
+ *
  * Due to the use of toggle references in the python and python3
  * bindings only one of them should be enabled. Otherwise vast
  * memory leaks are to be expected and as such it is an error to
diff --git a/loaders/lua5.1/peas-plugin-loader-lua.c b/loaders/lua5.1/peas-plugin-loader-lua.c
index ccc0ad0..66e0838 100644
--- a/loaders/lua5.1/peas-plugin-loader-lua.c
+++ b/loaders/lua5.1/peas-plugin-loader-lua.c
@@ -335,6 +335,10 @@ peas_plugin_loader_lua_initialize (PeasPluginLoader *loader)
   PeasPluginLoaderLua *lua_loader = PEAS_PLUGIN_LOADER_LUA (loader);
   lua_State *L;
 
+  /* Add locking to support global plugin loaders.
+   * Blocked by: https://github.com/pavouk/lgi/issues/92
+   */
+
   L = luaL_newstate ();
   if (L == NULL)
     {