[gjs/gnome-3-28] object: Queue a forced GC when toggling down

[Philip Chimento <pchimento src gnome org>]

commit cd17a77322908bd41f60d1e29811073c241dd735
Author: Georges Basile Stavracas Neto <georges stavracas gmail com>
Date:   Wed Mar 28 19:21:52 2018 -0300

    object: Queue a forced GC when toggling down
    
    During a GC, the collector asks each object which other
    objects that it wants to hold on to so if there's an entire
    section of the heap graph that's not connected to anything
    else, and not reachable from the root set, then it can be
    trashed all at once.
    
    GObjects, however, don't work like that, there's only a
    reference count but no notion of who owns the reference so,
    a JS object that's proxying a GObject is unconditionally held
    alive as long as the GObject has >1 references.
    
    Since we cannot know how many more wrapped GObjects are going
    be marked for garbage collection after the owner is destroyed,
    always queue a garbage collection when a toggle reference goes
    down.
    
    Issue: #140
    
    (cherry picked from commit e9e969553866b0dd29e78b41c0e372569405f46c)

 gi/object.cpp         | 22 ++++++++++++++++++++++
 gjs/context-private.h |  2 +-
 gjs/context.cpp       | 14 ++++++++------
 3 files changed, 31 insertions(+), 7 deletions(-)
---
diff --git a/gi/object.cpp b/gi/object.cpp
index 98b83a76..913823d0 100644
--- a/gi/object.cpp
+++ b/gi/object.cpp
@@ -1072,8 +1072,30 @@ handle_toggle_down(GObject *gobj)
      * collected by the GC
      */
     if (priv->keep_alive.rooted()) {
+        GjsContext *context;
+
         gjs_debug_lifecycle(GJS_DEBUG_GOBJECT, "Unrooting object");
         priv->keep_alive.switch_to_unrooted();
+
+        /* During a GC, the collector asks each object which other
+         * objects that it wants to hold on to so if there's an entire
+         * section of the heap graph that's not connected to anything
+         * else, and not reachable from the root set, then it can be
+         * trashed all at once.
+         *
+         * GObjects, however, don't work like that, there's only a
+         * reference count but no notion of who owns the reference so,
+         * a JS object that's proxying a GObject is unconditionally held
+         * alive as long as the GObject has >1 references.
+         *
+         * Since we cannot know how many more wrapped GObjects are going
+         * be marked for garbage collection after the owner is destroyed,
+         * always queue a garbage collection when a toggle reference goes
+         * down.
+         */
+        context = gjs_context_get_current();
+        if (!_gjs_context_destroying(context))
+            _gjs_context_schedule_gc(context);
     }
 }
 
diff --git a/gjs/context-private.h b/gjs/context-private.h
index c45c8d05..49c0cf9e 100644
--- a/gjs/context-private.h
+++ b/gjs/context-private.h
@@ -36,7 +36,7 @@ bool         _gjs_context_destroying                  (GjsContext *js_context);
 
 void         _gjs_context_schedule_gc_if_needed       (GjsContext *js_context);
 
-void _gjs_context_schedule_gc (GjsContext *js_context);
+void _gjs_context_schedule_gc(GjsContext *js_context);
 
 void _gjs_context_exit(GjsContext *js_context,
                        uint8_t     exit_code);
diff --git a/gjs/context.cpp b/gjs/context.cpp
index 77d7eaa2..a2ce34ae 100644
--- a/gjs/context.cpp
+++ b/gjs/context.cpp
@@ -599,31 +599,33 @@ trigger_gc_if_needed (gpointer user_data)
     else
         gjs_gc_if_needed(js_context->context);
 
+    js_context->force_gc = false;
+
     return G_SOURCE_REMOVE;
 }
 
 
 static void
-_gjs_context_schedule_gc_internal (GjsContext *js_context,
-                                   bool        force_gc)
+_gjs_context_schedule_gc_internal(GjsContext *js_context,
+                                  bool        force_gc)
 {
     if (js_context->auto_gc_id > 0)
-        g_source_remove(js_context->auto_gc_id);
+        return;
 
-    js_context->force_gc = force_gc;
+    js_context->force_gc |= force_gc;
     js_context->auto_gc_id = g_idle_add_full(G_PRIORITY_LOW,
                                              trigger_gc_if_needed,
                                              js_context, NULL);
 }
 
 void
-_gjs_context_schedule_gc (GjsContext *js_context)
+_gjs_context_schedule_gc(GjsContext *js_context)
 {
     _gjs_context_schedule_gc_internal(js_context, true);
 }
 
 void
-_gjs_context_schedule_gc_if_needed (GjsContext *js_context)
+_gjs_context_schedule_gc_if_needed(GjsContext *js_context)
 {
     _gjs_context_schedule_gc_internal(js_context, false);
 }