<Swing Dev> RFR: [Regression] Switch of Gnome theme ends up in deadlocked UI

[Jayashree Sk1]

Hello,

Please review the fix for the following issue:
https://bugs.openjdk.java.net/browse/JDK-8244088

The scenario is:
Every-time we tried to switch a Gnome theme, Java ended up n deadlocked UI.

This regression was introduced (by below patches) while Providing GTK3 support in Java
Java8: 8207322: Backport GTK3 support on Linux to 8u
JDK11 : 8145547: [AWT/Swing] Conditional support for GTK 3 on Linux

Here for GTK3's g_main_context_iteration they have included an extra lock which was causing a deadlock and also the JNDI corresponding module is defined using a single parameter causing the hang in XToolkit_waitForEvents


So the fix is in 2 parts:

1) In Java_com_sun_java_swing_plaf_gtk_GTKEngine_native_1switch_1theme () method we wrap the g_main_context_iteration (ie, gtk->flush_event_loop() ) with gdk_threads_enter/gdk_threads_exit while g_main_context_iteration itself takes care of locks.

-> Remove the extra lock

2) The definition of g_main_context_iteration in new “gtk3_interface.h” was wrongly written with a single parameter, like :
static gboolean (*fp_g_main_context_iteration)(GMainContext *context);


instead of https://developer.gnome.org/glib/stable/glib-The-Main-Event-Loop.html#g-main-context-iteration
gboolean            g_main_context_iteration            (GMainContext *context,
                                                         gboolean may_block);

-> When the above definition was corrected, we stopped seeing the hang during polling. 



The proposed changeset is:

--- old/src/java.desktop/unix/native/libawt_xawt/awt/gtk3_interface.c	2020-08-25 16:57:34.000000000 +0530
+++ new/src/java.desktop/unix/native/libawt_xawt/awt/gtk3_interface.c	2020-08-25 16:57:34.000000000 +0530
@@ -703,7 +703,7 @@
  */
 static void flush_gtk_event_loop()
 {
-    while((*fp_g_main_context_iteration)(NULL));
+    while((*fp_g_main_context_iteration)(NULL, FALSE));
 }
 
 /*


--- old/src/java.desktop/unix/native/libawt_xawt/awt/gtk3_interface.h	2020-08-25 16:57:36.000000000 +0530
+++ new/src/java.desktop/unix/native/libawt_xawt/awt/gtk3_interface.h	2020-08-25 16:57:35.000000000 +0530
@@ -396,7 +396,7 @@
                                        const gchar *first_property_name,
                                        ...);
 
-static gboolean (*fp_g_main_context_iteration)(GMainContext *context);
+static gboolean (*fp_g_main_context_iteration)(GMainContext *context, gboolean may_block);
 static gboolean (*fp_g_str_has_prefix)(const gchar *str, const gchar *prefix);
 static gchar** (*fp_g_strsplit)(const gchar *string, const gchar *delimiter,
            gint max_tokens);


--- old/src/java.desktop/unix/native/libawt_xawt/awt/swing_GTKEngine.c	2020-08-25 16:57:37.000000000 +0530
+++ new/src/java.desktop/unix/native/libawt_xawt/awt/swing_GTKEngine.c	2020-08-25 16:57:37.000000000 +0530
@@ -346,10 +346,8 @@
 JNIEXPORT void JNICALL Java_com_sun_java_swing_plaf_gtk_GTKEngine_native_1switch_1theme(
         JNIEnv *env, jobject this)
 {
-    // Note that flush_gtk_event_loop takes care of locks (7053002)
-    gtk->gdk_threads_enter();
+    // Note that gtk->flush_event_loop takes care of locks (7053002)
     gtk->flush_event_loop();
-    gtk->gdk_threads_leave();
 }
 
 /*


Thanks
Jay