JVM crashes on setting callback for GTK3 signals

[praj-foss]

Hello there!

I'm currently learning JNR by trying out various Linux libraries, most recently GTK3. I used this example as a reference and wrote the new demo that can be found here. But it crashes badly when I try to run it (using ./gradlew gtk3:run). Here's the crash log: hs_err_pid10169.log. I use GraalVM 21.3.0 as my JDK 11 on a x86_64 Linux machine (openSUSE tumbleweed). My installed GTK version is 3.24.30-2.3.

I can see that it crashes on line 31 of Gtk3App.java where I call from Java

lib.g_signal_connect_data(application, "activate", onActivate, null, null, 0);

The onActivate is a lambda looking like this:

LibGtk3.GCallback onActivate = (app, data) -> {
    var window = lib.gtk_application_window_new(app);
    var button = lib.gtk_button_new_wih_label("Click me");
    lib.gtk_container_add(window, button);
    lib.gtk_widget_show_all(window);
};

which is supposed to act like a function pointer similar to on_app_activate from my C reference:

// callback function which is called when application is first started
static void on_app_activate(GApplication *app, gpointer data) {
    // create a new application window for the application
    // GtkApplication is sub-class of GApplication
    // downcast GApplication* to GtkApplication* with GTK_APPLICATION() macro
    GtkWidget *window = gtk_application_window_new(GTK_APPLICATION(app));
    // a simple push button
    GtkWidget *btn = gtk_button_new_with_label("Click Me!");
    // connect the event-handler for "clicked" signal of button
    g_signal_connect(btn, "clicked", G_CALLBACK(on_button_clicked), NULL);
    // add the button to the window
    gtk_container_add(GTK_CONTAINER(window), btn);
    // display the window
    gtk_widget_show_all(GTK_WIDGET(window));
}

You can use https://github.com/praj-foss/jnr-demo to reproduce it using ./gradlew gtk3:run. The crash depends on the system as well: it ran perfectly fine on openSUSE leap 15.2, Mac OS, and Fedora Core 34 (verified by @headius and @enebo), but it crashed on openSUSE Tumbleweed and Ubuntu 21.10.

NOTE: This issue was earlier opened in jnr/jnr-ffi#281

[headius]

Note the difference between this issue and jnr/jnr-ffi#281 is that the latter turned out to be mostly due to a mistake in the client code that caused a bad pointer to be passed out to C. Fixing that fixed the issue for me and @enebo but exposed a new crash within jffi for @praj-foss. I asked them to re-open as a jffi issue so we could investigate the problem.

[headius]

Since we are not currently able to reproduce this issue, I repost what I know about enabling a debug build of jffi:

I believe this diff followed by running ant should get you a jffi binary that has debug symbols:

diff --git a/jni/GNUmakefile b/jni/GNUmakefile
index cfe570a..4a8a061 100755
--- a/jni/GNUmakefile
+++ b/jni/GNUmakefile
@@ -61,7 +61,7 @@ LIBNAME = jffi
 # Compiler/linker flags from:
 #   http://weblogs.java.net/blog/kellyohair/archive/2006/01/compilation_of_1.html
 JFLAGS = -fno-omit-frame-pointer -fno-strict-aliasing -DNDEBUG
-OFLAGS = -O2 $(JFLAGS)
+OFLAGS = -Og -g $(JFLAGS)
 
 # MacOS headers aren't completely warning free, so turn them off
 WERROR = -Werror

We have no leads as to why this particular example crashes inside jffi only on some platforms.