From 58f2d3fbe74cee306fa666c087a985edecdccaa4 Mon Sep 17 00:00:00 2001
From: Emmanuele Bassi <ebassi@gnome.org>
Date: Mon, 27 May 2024 13:09:55 +0100
Subject: [PATCH] a11y: Add reference counting to event listeners

Event listeners can register themselves multiple times, and deregister
themselves as well. We need to remove an event listener only if it
dropped all its events.
---
 gtk/a11y/gtkatspiroot.c | 83 +++++++++++++++++++++++++++++++----------
 1 file changed, 63 insertions(+), 20 deletions(-)

diff --git a/gtk/a11y/gtkatspiroot.c b/gtk/a11y/gtkatspiroot.c
index 2ba47f03aa..d69582d23c 100644
--- a/gtk/a11y/gtkatspiroot.c
+++ b/gtk/a11y/gtkatspiroot.c
@@ -73,7 +73,7 @@ struct _GtkAtSpiRoot
 
   GListModel *toplevels;
 
-  /* HashTable<str, str> */
+  /* HashTable<str, uint> */
   GHashTable *event_listeners;
 };
 
@@ -504,19 +504,34 @@ on_event_listener_registered (GDBusConnection *connection,
       char *sender = NULL;
       char *event_name = NULL;
       char **event_types = NULL;
+      unsigned int *count;
 
       if (self->event_listeners == NULL)
         self->event_listeners = g_hash_table_new_full (g_str_hash, g_str_equal,
                                                        g_free,
-                                                       NULL);
+                                                       g_free);
 
       g_variant_get (parameters, "(ssas)", &sender, &event_name, &event_types);
 
-      GTK_DEBUG (A11Y, "Registering event listener (%s, %s) on the a11y bus",
-                 sender,
-                 event_name[0] != 0 ? event_name : "(none)");
-
-      g_hash_table_add (self->event_listeners, sender);
+      count = g_hash_table_lookup (self->event_listeners, sender);
+      if (count == NULL)
+        {
+          GTK_DEBUG (A11Y, "Registering event listener (%s, %s) on the a11y bus",
+                     sender,
+                     event_name[0] != 0 ? event_name : "(none)");
+          count = g_new (unsigned int, 1);
+          *count = 1;
+          g_hash_table_insert (self->event_listeners, sender, count);
+        }
+      else if (*count == G_MAXUINT)
+        {
+          g_critical ("Reference count for event listener %s reached saturation", sender);
+        }
+      else
+        {
+          GTK_DEBUG (A11Y, "Incrementing refcount for event listener %s", sender);
+          *count += 1;
+        }
 
       g_free (event_name);
       g_strfreev (event_types);
@@ -540,22 +555,37 @@ on_event_listener_deregistered (GDBusConnection *connection,
     {
       const char *sender = NULL;
       const char *event = NULL;
-
-      if (self->event_listeners == NULL)
-        {
-          g_critical ("Received org.a11y.atspi.Registry::EventListenerDeregistered without "
-                      "a corresponding EventListenerRegistered signal.");
-          return;
-        }
+      unsigned int *count;
 
       g_variant_get (parameters, "(&s&s)", &sender, &event);
 
-      if (g_hash_table_contains (self->event_listeners, sender))
+      if (G_UNLIKELY (self->event_listeners == NULL))
         {
-          GTK_DEBUG (A11Y, "Deregistering event listener (%s, %s) on the a11y bus",
-                     sender,
-                     event[0] != 0 ? event : "(none)");
+          g_critical ("Received org.a11y.atspi.Registry::EventListenerDeregistered for "
+                      "sender (%s, %s) without a corresponding EventListenerRegistered "
+                      "signal.",
+                      sender, event[0] != '\0' ? event : "(no event)");
+          return;
+        }
 
+      count = g_hash_table_lookup (self->event_listeners, sender);
+      if (G_UNLIKELY (count == NULL))
+        {
+          g_critical ("Received org.a11y.atspi.Registry::EventListenerDeregistered for "
+                      "sender (%s, %s) without a corresponding EventListenerRegistered "
+                      "signal.",
+                      sender, event[0] != '\0' ? event : "(no event)");
+          return;
+        }
+
+      if (*count > 1)
+        {
+          GTK_DEBUG (A11Y, "Decreasing refcount for listener %s", sender);
+          *count -= 1;
+        }
+      else
+        {
+          GTK_DEBUG (A11Y, "Deregistering event listener %s on the a11y bus", sender);
           g_hash_table_remove (self->event_listeners, sender);
         }
     }
@@ -586,12 +616,25 @@ on_registered_events_reply (GObject *gobject,
   g_variant_get (listeners, "a(ss)", &iter);
   while (g_variant_iter_loop (iter, "(&s&s)", &sender, &event_name))
     {
+      unsigned int *count;
+
       GTK_DEBUG (A11Y, "Registering event listener (%s, %s) on the a11y bus",
                  sender,
                  event_name[0] != 0 ? event_name : "(none)");
 
-      if (!g_hash_table_contains (self->event_listeners, sender))
-        g_hash_table_add (self->event_listeners, g_strdup (sender));
+      count = g_hash_table_lookup (self->event_listeners, sender);
+      if (count == NULL)
+        {
+          count = g_new (unsigned int, 1);
+          *count = 1;
+          g_hash_table_insert (self->event_listeners, g_strdup (sender), count);
+        }
+      else if (*count == G_MAXUINT)
+        {
+          g_critical ("Reference count for event listener %s reached saturation", sender);
+        }
+      else
+        *count += 1;
     }
 
   g_variant_iter_free (iter);