Steps to reproduce:
By uncommenting the line containing JPanel - the jvm will crash.
Java VM: Java HotSpot(TM) Client VM (1.5.0_04-b05 mixed mode, sharing)

import javax.swing.JPanel;

import org.gnu.glib.CustomEvents;
import org.gnu.gtk.Gtk;
import org.gnu.gtk.Window;

public class CustomEventTest {

	public static void main(String[] args) {
		//JPanel panel = new JPanel();
	
		Thread t = new Thread(new Runnable() {
			public void run() {
				Gtk.init(null);
				Gtk.main();
			}
		});
		t.start();
		
		CustomEvents.addEvent(new Runnable() {
			public void run() {
				Window w = new Window();
				w.showAll();
			}
		});
	}
}

Stack trace:
Stack: [0xb1a32000,0xb1ab2000),  sp=0xb1ab0b70,  free space=506k
Native frames: (J=compiled Java code, j=interpreted, Vv=VM code, C=native code)
C  [libjava.so+0x118ac]  JNU_GetEnv+0x1c
C  [libgtkjni-2.8.so+0x80086]  function+0x16
C  [libgtkjni-2.8.so+0x8011d]  dispatch+0xd
C  [libglib-2.0.so.0+0x23a61]  g_main_context_dispatch+0x211
C  [libglib-2.0.so.0+0x26cb7]
C  [libglib-2.0.so.0+0x27208]  g_main_loop_run+0x1a8
C  [libgtk-x11-2.0.so.0+0x12d019]  gtk_main+0xb9
C  [libgtkjni-2.8.so+0x8f996]  Java_org_gnu_gtk_Gtk_gtk_1main+0x16
j  org.gnu.gtk.Gtk.gtk_main()V+0
j  org.gnu.gtk.Gtk.main()V+6
j  CustomEventTest$1.run()V+4
j  java.lang.Thread.run()V+11
v  ~StubRoutines::call_stub
V  [libjvm.so+0x16bf8c]
V  [libjvm.so+0x25e5f8]
V  [libjvm.so+0x16b7e5]
V  [libjvm.so+0x16b87e]
V  [libjvm.so+0x1d0fd5]
V  [libjvm.so+0x2b76d3]
V  [libjvm.so+0x25f108]
C  [libpthread.so.0+0x51ee]

Java frames: (J=compiled Java code, j=interpreted, Vv=VM code)
j  org.gnu.gtk.Gtk.gtk_main()V+0
j  org.gnu.gtk.Gtk.main()V+6
j  CustomEventTest$1.run()V+4
j  java.lang.Thread.run()V+11
v  ~StubRoutines::call_stub


Other information:
The crash happens in JNU_GetEnv. Most probably cached_jvm is null when we have a
swing component - but this need to be checked.

Note - the above code works fine with gij:

java version "1.4.2"
gij (GNU libgcj) version 4.0.3 20051023 (prerelease) (Ubuntu 4.0.2-3ubuntu1)