hook the plugin refcounting in

The plugin refcounter is driven from interface opening/closing, this is
quite internal.

The 'last' time in plugin now records the last time the refcounter dropped
to 0, this is just sufficient enough to find out how long a plugin is
unused.

src/backend/interface.c

@@ -22,6 +22,7 @@
 #include "lib/mutex.h"
 #include "lib/safeclib.h"
 
+#include "backend/plugin.h"
 #include "backend/interface.h"
 
 #include "backend/interfaceregistry.h"
@@ -133,8 +134,9 @@ depwalk (LumieraInterfacenode self, LumieraInterfacenode* stack)
 
           if (!cycle)
             {
+              if ((*dep)->plugin)
+                lumiera_plugin_refinc ((*dep)->plugin);
               ++(*dep)->refcnt;
-
               (*dep)->lnk = *stack;
               *stack = *dep;
 
@@ -184,7 +186,10 @@ lumiera_interface_open_interfacenode (LumieraInterfacenode self)
 
           if (!cycle)
             {
+              if (self->plugin)
+                lumiera_plugin_refinc (self->plugin);
               ++self->refcnt;
+
               self->lnk = stack;
               stack = self;
               int collect_dependencies_bak = collect_dependencies;
@@ -290,6 +295,8 @@ lumiera_interfacenode_close (LumieraInterfacenode self)
 
       stack = self->lnk;
       self->lnk = NULL;
+      if (self->plugin)
+        lumiera_plugin_refdec (self->plugin);
       --self->refcnt;
     }
 }

src/backend/interfaceregistry.c

@@ -65,7 +65,6 @@ lumiera_interfacenode_new (LumieraInterface iface, LumieraPlugin plugin)
   self->interface = iface;
   self->refcnt = 0;
   self->plugin = plugin;
-  FIXME ("plugin handling (refcnt, atime)");
   self->lnk = NULL;
   self->deps_size = 0;
   self->deps = NULL;
@@ -80,7 +79,6 @@ lumiera_interfacenode_delete (LumieraInterfacenode self)
   if (self)
     {
       REQUIRE (self->refcnt == 0);
-      FIXME ("plugin handling");
       lumiera_free (self->deps);
       lumiera_free (self);
     }

src/backend/plugin.c

@@ -107,7 +107,7 @@ struct lumiera_plugin_struct
   /* use count for all interfaces of this plugin */
   unsigned refcnt;
 
-  /* time when the last open or close action happened */
+  /* time when the refcounter dropped to 0 last time */
   time_t last;
 
   /* when loading plugins en masse we do not want to fail completely if one doesnt cooperate, instead we record local errors here */
@@ -180,7 +180,8 @@ lumiera_plugin_refinc (LumieraPlugin self)
 void
 lumiera_plugin_refdec (LumieraPlugin self)
 {
-  --self->refcnt;
+  if (!--self->refcnt)
+    time (&self->last);
 }