[libpeas] Fix Lua plugins to work with multiple threads

[Garrett Regier <gregier src gnome org>]

commit 6040c22fef0cdf7ee94876aaed37c86bcf92e25f
Author: Garrett Regier <garrett regier riftio com>
Date:   Tue Dec 16 01:42:21 2014 -0800

    Fix Lua plugins to work with multiple threads
    
    Unlock the LGI lock after init and acquire and release it
    as necessary. This allows plugins to be used from multiple
    threads and global plugin loader limitations.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=741579

 libpeas/peas-engine.c                     |    7 +---
 loaders/lua5.1/peas-plugin-loader-lua.c   |   64 +++++++++++++++++++++++++----
 tests/libpeas/testing/testing-extension.c |    9 +---
 3 files changed, 58 insertions(+), 22 deletions(-)
---
diff --git a/libpeas/peas-engine.c b/libpeas/peas-engine.c
index ed87ea7..11a3774 100644
--- a/libpeas/peas-engine.c
+++ b/libpeas/peas-engine.c
@@ -822,11 +822,6 @@ 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. This can be be avoided by using
- * peas_engine_new_with_nonglobal_loaders().
- *
  * Note: plugin loaders used to be shared across #PeasEngines so enabling
  *       a loader on one #PeasEngine would enable it on all #PeasEngines.
  *       This behavior has been kept to avoid breaking applications,
@@ -1431,7 +1426,7 @@ peas_engine_new (void)
  * Note: due to CPython's GIL the python and python3
  *       plugin loaders are always global.
  *
- * Returns: a new instance of #PeasEngine that uses nonglobal loaders.
+ * Returns: a new instance of #PeasEngine that uses non-global loaders.
  *
  * Since: 1.14
  */
diff --git a/loaders/lua5.1/peas-plugin-loader-lua.c b/loaders/lua5.1/peas-plugin-loader-lua.c
index fdb4a3f..21208eb 100644
--- a/loaders/lua5.1/peas-plugin-loader-lua.c
+++ b/loaders/lua5.1/peas-plugin-loader-lua.c
@@ -34,8 +34,15 @@
 #include "peas-plugin-loader-lua-utils.h"
 
 
+typedef void (* LgiLockFunc) (gpointer lgi_lock);
+
+
 struct _PeasPluginLoaderLuaPrivate {
   lua_State *L;
+
+  gpointer lgi_lock;
+  LgiLockFunc lgi_enter_func;
+  LgiLockFunc lgi_leave_func;
 };
 
 G_DEFINE_TYPE (PeasPluginLoaderLua, peas_plugin_loader_lua, PEAS_TYPE_PLUGIN_LOADER)
@@ -197,7 +204,9 @@ peas_plugin_loader_lua_provides_extension (PeasPluginLoader *loader,
   lua_State *L = lua_loader->priv->L;
   GType extension_type;
 
+  lua_loader->priv->lgi_enter_func (lua_loader->priv->lgi_lock);
   extension_type = _lua_find_extension_type (L, info, exten_type);
+  lua_loader->priv->lgi_leave_func (lua_loader->priv->lgi_lock);
 
   return extension_type != G_TYPE_INVALID;
 }
@@ -212,21 +221,23 @@ peas_plugin_loader_lua_create_extension (PeasPluginLoader *loader,
   PeasPluginLoaderLua *lua_loader = PEAS_PLUGIN_LOADER_LUA (loader);
   lua_State *L = lua_loader->priv->L;
   GType the_type;
-  GObject *object;
+  GObject *object = NULL;
+
+  lua_loader->priv->lgi_enter_func (lua_loader->priv->lgi_lock);
 
   the_type = _lua_find_extension_type (L, info, exten_type);
   if (the_type == G_TYPE_INVALID)
-    return NULL;
+    goto out;
 
   if (!g_type_is_a (the_type, exten_type))
     {
       g_warn_if_fail (g_type_is_a (the_type, exten_type));
-      return NULL;
+      goto out;
     }
 
   object = g_object_newv (the_type, n_parameters, parameters);
   if (object == NULL)
-    return NULL;
+    goto out;
 
   /* We have to remember which interface we are instantiating
    * for the deprecated peas_extension_get_extension_type().
@@ -239,7 +250,7 @@ peas_plugin_loader_lua_create_extension (PeasPluginLoader *loader,
   if (!_lua_pushinstance (L, "GObject", "Object", the_type, object))
     {
       g_clear_object (&object);
-      return NULL;
+      goto out;
     }
 
   lua_getfield (L, -1, "priv");
@@ -258,6 +269,9 @@ peas_plugin_loader_lua_create_extension (PeasPluginLoader *loader,
   /* Pop priv and object */
   lua_pop (L, 2);
 
+out:
+
+  lua_loader->priv->lgi_leave_func (lua_loader->priv->lgi_lock);
   return object;
 }
 
@@ -269,6 +283,8 @@ peas_plugin_loader_lua_load (PeasPluginLoader *loader,
   lua_State *L = lua_loader->priv->L;
   gboolean success;
 
+  lua_loader->priv->lgi_enter_func (lua_loader->priv->lgi_lock);
+
   luaL_checkstack (L, 2, "");
 
   /* Get the module's table */
@@ -303,6 +319,7 @@ peas_plugin_loader_lua_load (PeasPluginLoader *loader,
   /* Pop the module's table */
   lua_pop (L, 1);
 
+  lua_loader->priv->lgi_leave_func (lua_loader->priv->lgi_lock);
   return success;
 }
 
@@ -318,7 +335,9 @@ peas_plugin_loader_lua_garbage_collect (PeasPluginLoader *loader)
 {
   PeasPluginLoaderLua *lua_loader = PEAS_PLUGIN_LOADER_LUA (loader);
 
+  lua_loader->priv->lgi_enter_func (lua_loader->priv->lgi_lock);
   lua_gc (lua_loader->priv->L, LUA_GCCOLLECT, 0);
+  lua_loader->priv->lgi_leave_func (lua_loader->priv->lgi_lock);
 }
 
 static int
@@ -334,10 +353,6 @@ 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)
     {
@@ -358,6 +373,27 @@ peas_plugin_loader_lua_initialize (PeasPluginLoader *loader)
       return FALSE;
     }
 
+  lua_getfield (L, -1, "lock");
+  lua_loader->priv->lgi_lock = lua_touserdata (L, -1);
+  lua_pop (L, 1);
+
+  lua_getfield (L, -1, "enter");
+  lua_loader->priv->lgi_enter_func = lua_touserdata (L, -1);
+  lua_pop (L, 1);
+
+  lua_getfield (L, -1, "leave");
+  lua_loader->priv->lgi_leave_func = lua_touserdata (L, -1);
+  lua_pop (L, 1);
+
+  if (lua_loader->priv->lgi_lock == NULL ||
+      lua_loader->priv->lgi_enter_func == NULL ||
+      lua_loader->priv->lgi_leave_func == NULL)
+    {
+      g_warning ("Failed to find 'lgi.lock', 'lgi.enter' and 'lgi.leave'");
+      lua_close (L);
+      return FALSE;
+    }
+
   /* Pop lgi's module table */
   lua_pop (L, 1);
 
@@ -366,6 +402,11 @@ peas_plugin_loader_lua_initialize (PeasPluginLoader *loader)
       lua_atpanic (L, atpanic_handler);
     }
 
+  /* Initially the lock is taken by LGI,
+   * release as we are not running Lua code
+   */
+  lua_loader->priv->lgi_leave_func (lua_loader->priv->lgi_lock);
+
   lua_loader->priv->L = L;
   return TRUE;
 }
@@ -389,6 +430,11 @@ peas_plugin_loader_lua_finalize (GObject *object)
 {
   PeasPluginLoaderLua *lua_loader = PEAS_PLUGIN_LOADER_LUA (object);
 
+  /* Must take the lock as Lua code will run on lua_close
+   * and another thread might be running Lua code already
+   */
+  lua_loader->priv->lgi_enter_func (lua_loader->priv->lgi_lock);
+
   g_clear_pointer (&lua_loader->priv->L, (GDestroyNotify) lua_close);
 
   G_OBJECT_CLASS (peas_plugin_loader_lua_parent_class)->finalize (object);
diff --git a/tests/libpeas/testing/testing-extension.c b/tests/libpeas/testing/testing-extension.c
index d5dba02..51fb2e6 100644
--- a/tests/libpeas/testing/testing-extension.c
+++ b/tests/libpeas/testing/testing-extension.c
@@ -505,13 +505,8 @@ testing_extension_basic (const gchar *loader_)
   _EXTENSION_TEST (loader, "plugin-info", plugin_info);
   _EXTENSION_TEST (loader, "get-settings", get_settings);
 
-  /* See peas_engine_enable_loader() */
-  if (g_strcmp0 (loader, "lua5.1") != 0)
-    {
-      _EXTENSION_TEST (loader, "multiple-threads/global-loaders",
-                       multiple_threads_global_loaders);
-    }
-
+  _EXTENSION_TEST (loader, "multiple-threads/global-loaders",
+                   multiple_threads_global_loaders);
   _EXTENSION_TEST (loader, "multiple-threads/nonglobal-loaders",
                    multiple_threads_nonglobal_loaders);
 }