gjs/gjs-Queue-forced-GC.patch

From e9e969553866b0dd29e78b41c0e372569405f46c Mon Sep 17 00:00:00 2001
From: Georges Basile Stavracas Neto <georges.stavracas@gmail.com>
Date: Wed, 28 Mar 2018 19:21:52 -0300
Subject: [PATCH] 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
---
 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 3fdfced..606a918 100644
--- a/gi/object.cpp
+++ b/gi/object.cpp
@@ -1001,8 +1001,30 @@ 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 c45c8d0..49c0cf9 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 77d7eaa..a2ce34a 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);
 }
--
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