cogl-pipeline: Fix reference counting on promoting weak parents

When a copy is made of a weak pipeline it tries to promote the weak
parent by taking a reference on that weak pipeline's parent. However
promote_weak_ancestors was instead always taking a reference on the
first parent, regardless of whether it was weak. The corresponding
revert_weak_ancestors function which is supposed to undo the effect of
promote_weak_ancestors only unref'd the parent if was weak. This meant
that any non-weak pipeline copy would end up leaking a reference on
its parent.

This patch changes both functions to have a similar loop. It loops
through all of the parents of the pipeline until it finds one that is
not weak and refs or unrefs the *parent* of that pipeline instead of
the pipeline itself.

This is cherry-picked from 17a558a386 on Cogl git master.

1 files changed, 21 insertions, 18 deletions

diff --git a/clutter/cogl/cogl/cogl-pipeline.c b/clutter/cogl/cogl/cogl-pipeline.c
index acce53683..5f2024ad2 100644
--- a/clutter/cogl/cogl/cogl-pipeline.c
+++ b/clutter/cogl/cogl/cogl-pipeline.c
@@ -394,37 +394,40 @@ _cogl_pipeline_promote_weak_ancestors (CoglPipeline *strong)
 
   g_return_if_fail (!strong->is_weak);
 
-  for (n = COGL_PIPELINE_NODE (strong)->parent; n; n = n->parent)
-    {
-      CoglPipeline *pipeline = COGL_PIPELINE (n);
+  /* If the parent of strong is weak, then we want to promote it by
+     taking a reference on strong's grandparent. We don't need to take
+     a reference on strong's direct parent */
 
-      cogl_object_ref (pipeline);
+  if (COGL_PIPELINE_NODE (strong)->parent == NULL)
+    return;
 
-      if (!pipeline->is_weak)
-        return;
-    }
+  for (n = COGL_PIPELINE_NODE (strong)->parent;
+       /* We can assume that all weak pipelines have a parent */
+       COGL_PIPELINE (n)->is_weak;
+       n = n->parent)
+    /* 'pipeline' is weak so we take a reference on its parent */
+    cogl_object_ref (n->parent);
 }
 
 static void
 _cogl_pipeline_revert_weak_ancestors (CoglPipeline *strong)
 {
-  CoglPipeline *parent = _cogl_pipeline_get_parent (strong);
   CoglPipelineNode *n;
 
   g_return_if_fail (!strong->is_weak);
 
-  if (!parent || !parent->is_weak)
-    return;
-
-  for (n = COGL_PIPELINE_NODE (strong)->parent; n; n = n->parent)
-    {
-      CoglPipeline *pipeline = COGL_PIPELINE (n);
+  /* This reverts the effect of calling
+     _cogl_pipeline_promote_weak_ancestors */
 
-      cogl_object_unref (pipeline);
+  if (COGL_PIPELINE_NODE (strong)->parent == NULL)
+    return;
 
-      if (!pipeline->is_weak)
-        return;
-    }
+  for (n = COGL_PIPELINE_NODE (strong)->parent;
+       /* We can assume that all weak pipelines have a parent */
+       COGL_PIPELINE (n)->is_weak;
+       n = n->parent)
+    /* 'pipeline' is weak so we take a reference on its parent */
+    cogl_object_unref (n->parent);
 }
 
 /* XXX: Always have an eye out for opportunities to lower the cost of