[java-atk-wrapper] Compact data changed events queue

[Samuel Thibault <sthibaul src gnome org>]

commit f8745523b8ee7e77111b555ed44a856341d5110f
Author: Samuel Thibault <samuel thibault ens-lyon org>
Date:   Thu Aug 15 11:55:15 2019 +0200

    Compact data changed events queue
    
    OpenJDK seems to be sending flurries of visible data changed events, which
    overloads us. They are however usually just for the same object, so we can
    compact them: there is no need to queue another one if the previous hasn't
    even been sent!

 jni/src/AtkWrapper.c | 44 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 44 insertions(+)
---
diff --git a/jni/src/AtkWrapper.c b/jni/src/AtkWrapper.c
index 35ed884..9a844f9 100644
--- a/jni/src/AtkWrapper.c
+++ b/jni/src/AtkWrapper.c
@@ -205,6 +205,7 @@ enum _SignalType {
 };
 
 typedef struct _CallbackPara {
+  jobject ac;
   jobject global_ac;
   JawImpl *jaw_impl;
   JawImpl *child_impl;
@@ -629,6 +630,15 @@ get_int_value (JNIEnv *jniEnv, jobject o)
   return (gint)(*jniEnv)->CallIntMethod(jniEnv, o, jmid);
 }
 
+/*
+ * OpenJDK seems to be sending flurries of visible data changed events, which
+ * overloads us. They are however usually just for the same object, so we can
+ * compact them: there is no need to queue another one if the previous hasn't
+ * even been sent!
+ */
+static pthread_mutex_t jaw_vdc_dup_mutex = PTHREAD_MUTEX_INITIALIZER;
+static jobject jaw_vdc_last_ac = NULL;
+
 static gboolean
 signal_emit_handler (gpointer p)
 {
@@ -638,6 +648,16 @@ signal_emit_handler (gpointer p)
   jobjectArray args = para->args;
   AtkObject* atk_obj = ATK_OBJECT(para->jaw_impl);
 
+  if (para->signal_id == Sig_Object_Visible_Data_Changed)
+  {
+    pthread_mutex_lock(&jaw_vdc_dup_mutex);
+    if (jaw_vdc_last_ac == para->ac)
+      /* So we will be sending the visible data changed event. If any other
+       * comes, we will want to send it  */
+      jaw_vdc_last_ac = NULL;
+    pthread_mutex_unlock(&jaw_vdc_dup_mutex);
+  }
+
   switch (para->signal_id)
   {
     case Sig_Text_Caret_Moved:
@@ -869,14 +889,38 @@ JNICALL Java_org_GNOME_Accessibility_AtkWrapper_emitSignal(JNIEnv *jniEnv,
                                                            jobjectArray args)
 {
   JAW_DEBUG_JNI("%p, %p, %p, %d, %p", jniEnv, jClass, jAccContext, id, args);
+
+  pthread_mutex_lock(&jaw_vdc_dup_mutex);
+  if (id != Sig_Object_Visible_Data_Changed)
+  {
+    /* Something may have happened since the last visible data changed event, so
+     * we want to sent it again */
+    jaw_vdc_last_ac = NULL;
+  }
+  else
+  {
+    if (jaw_vdc_last_ac == jAccContext)
+    {
+      /* We have already queued to send one and nothing happened in between,
+       * this one is really useless */
+      pthread_mutex_unlock(&jaw_vdc_dup_mutex);
+      return;
+    }
+
+    jaw_vdc_last_ac = jAccContext;
+  }
+  pthread_mutex_unlock(&jaw_vdc_dup_mutex);
+
   if (!jAccContext) {
     JAW_DEBUG_I("jAccContext == NULL");
     return;
   }
+
   jobject global_ac = (*jniEnv)->NewGlobalRef(jniEnv, jAccContext);
   callback_para_process_frees();
   jobjectArray global_args = (jobjectArray)(*jniEnv)->NewGlobalRef(jniEnv, args);
   CallbackPara *para = alloc_callback_para(jniEnv, global_ac);
+  para->ac = jAccContext;
   para->signal_id = (gint)id;
   para->args = global_args;
   switch (para->signal_id)