[libdazzle] cancellable: try harder with release with weak refs

[Christian Hergert <chergert src gnome org>]

commit aecb1d798e4ba515a424f8aa0303df0887ac5e29
Author: Christian Hergert <chergert redhat com>
Date:   Mon Jun 18 18:23:51 2018 -0700

    cancellable: try harder with release with weak refs
    
    This still isn't enough to catch a case I'm seeing in Builder, but it does
    increase our chances of releasing the structure sooner. If we loose any
    of our objects, we want to release the signal connection immediately (and
    ultimately the info struct).

 src/util/dzl-cancellable.c | 65 +++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 61 insertions(+), 4 deletions(-)
---
diff --git a/src/util/dzl-cancellable.c b/src/util/dzl-cancellable.c
index 208e202..c59de83 100644
--- a/src/util/dzl-cancellable.c
+++ b/src/util/dzl-cancellable.c
@@ -25,11 +25,16 @@
 #include "util/dzl-cancellable.h"
 #include "util/dzl-macros.h"
 
+#define CHAINED_INFO_MAGIC 0x81734637
+
 typedef struct
 {
-  GWeakRef self;
-  GWeakRef other;
-  gulong   other_handler;
+  guint         magic;
+  volatile gint ref_count;
+  GMutex        mutex;
+  GWeakRef      self;
+  GWeakRef      other;
+  gulong        other_handler;
 } ChainedInfo;
 
 static void
@@ -40,6 +45,10 @@ chained_info_free (gpointer data)
   g_autoptr(GCancellable) other = NULL;
 
   g_assert (info != NULL);
+  g_assert (info->magic == CHAINED_INFO_MAGIC);
+  g_assert (info->ref_count == 0);
+
+  info->magic = 0;
 
   self = g_weak_ref_get (&info->self);
   other = g_weak_ref_get (&info->other);
@@ -52,9 +61,37 @@ chained_info_free (gpointer data)
   g_weak_ref_clear (&info->other);
   g_weak_ref_clear (&info->self);
 
+  g_mutex_clear (&info->mutex);
+
   g_slice_free (ChainedInfo, info);
 }
 
+static void
+chained_info_unref (ChainedInfo *info)
+{
+  g_autoptr(GCancellable) other = NULL;
+
+  g_assert (info != NULL);
+  g_assert (info->ref_count > 0);
+  g_assert (info->magic == CHAINED_INFO_MAGIC);
+
+  if ((other = g_weak_ref_get (&info->other)))
+    {
+      gulong handler_id;
+
+      g_mutex_lock (&info->mutex);
+      handler_id = info->other_handler;
+      info->other_handler = 0;
+      g_mutex_unlock (&info->mutex);
+
+      if (handler_id)
+        g_signal_handler_disconnect (other, handler_id);
+    }
+
+  if (g_atomic_int_dec_and_test (&info->ref_count))
+    chained_info_free (info);
+}
+
 static void
 dzl_cancellable_cancelled_cb (GCancellable *other,
                               ChainedInfo  *info)
@@ -63,6 +100,8 @@ dzl_cancellable_cancelled_cb (GCancellable *other,
 
   g_assert (G_IS_CANCELLABLE (other));
   g_assert (info != NULL);
+  g_assert (info->ref_count > 0);
+  g_assert (info->magic == CHAINED_INFO_MAGIC);
 
   self = g_weak_ref_get (&info->self);
 
@@ -75,6 +114,19 @@ dzl_cancellable_cancelled_cb (GCancellable *other,
   dzl_clear_signal_handler (other, &info->other_handler);
 }
 
+static void
+dzl_cancellable_weak_cb (gpointer  data,
+                         GObject  *where_object_was)
+{
+  ChainedInfo *info = data;
+
+  g_assert (info != NULL);
+  g_assert (info->ref_count > 0);
+  g_assert (info->magic == CHAINED_INFO_MAGIC);
+
+  chained_info_unref (info);
+}
+
 /**
  * dzl_cancellable_chain:
  * @self: (nullable): a #GCancellable or %NULL
@@ -122,12 +174,17 @@ dzl_cancellable_chain (GCancellable *self,
    */
 
   info = g_slice_new0 (ChainedInfo);
+  info->magic = CHAINED_INFO_MAGIC;
+  info->ref_count = 3;
+  g_mutex_init (&info->mutex);
   g_weak_ref_init (&info->self, self);
   g_weak_ref_init (&info->other, other);
+  g_object_weak_ref (G_OBJECT (self), dzl_cancellable_weak_cb, info);
+  g_object_weak_ref (G_OBJECT (other), dzl_cancellable_weak_cb, info);
   info->other_handler = g_cancellable_connect (other,
                                                G_CALLBACK (dzl_cancellable_cancelled_cb),
                                                info,
-                                               chained_info_free);
+                                               (GDestroyNotify)chained_info_unref);
 
   return self;
 }