On Linux, if for some reason a control with InputMethodEvents enabled takes the focus too soon, before the application is shown, there is a crash:

(java:34229): Gdk-CRITICAL **: 11:48:19.249: gdk_window_get_display: assertion 'GDK_IS_WINDOW (window)' failed

(java:34229): Gdk-CRITICAL **: 11:48:19.249: gdk_x11_display_get_xdisplay: assertion 'GDK_IS_DISPLAY (display)' failed
#
# A fatal error has been detected by the Java Runtime Environment:
#
# SIGSEGV (0xb) at pc=0x00007f14985fca5d, pid=34229, tid=34269
#
# JRE version: OpenJDK Runtime Environment (23.0.1+11) (build 23.0.1+11-39)
# Java VM: OpenJDK 64-Bit Server VM (23.0.1+11-39, mixed mode, sharing, tiered, compressed oops, compressed class ptrs, g1 gc, linux-amd64)
# Problematic frame:
# C [libgdk-3.so.0+0x85a5d] gdk_x11_window_get_xid+0xd

The attached test contains a very simple control implementation with InputMethodEvents enabled that can be used to reproduce the issue.

Steps: run the application on Linux with a recent JDK 21 or later, and JavaFX 23.0.1 or later. It will crash immediately.

Current thread (0x00007f14c442da00): JavaThread "JavaFX Application Thread" [_thread_in_native, id=34269, stack(0x00007f14043b3000,0x00007f14044b3000) (1024K)]

Stack: [0x00007f14043b3000,0x00007f14044b3000], sp=0x00007f14044afe90, free space=1011k
Native frames: (J=compiled Java code, j=interpreted, Vv=VM code, C=native code)
C [libgdk-3.so.0+0x85a5d] gdk_x11_window_get_xid+0xd
j com.sun.glass.ui.gtk.GtkView.enableInputMethodEventsImpl(JZ)V+0 javafx.graphics@23.0.1
j com.sun.glass.ui.gtk.GtkView._enableInputMethodEvents(JZ)V+3 javafx.graphics@23.0.1
j com.sun.glass.ui.View.enableInputMethodEvents(Z)V+13 javafx.graphics@23.0.1
j com.sun.javafx.tk.quantum.ViewScene.enableInputMethodEvents(Z)V+5 javafx.graphics@23.0.1
j javafx.scene.Scene.enableInputMethodEvents(Z)V+12 javafx.graphics@23.0.1
j javafx.scene.Scene$FocusOwnerProperty.invalidated()V+74 javafx.graphics@23.0.1
j javafx.beans.property.ObjectPropertyBase.markInvalid()V+13 javafx.base@23.0.1
j javafx.beans.property.ObjectPropertyBase.set(Ljava/lang/Object;)V+72 javafx.base@23.0.1
j javafx.scene.Scene.setFocusOwner(Ljavafx/scene/Node;Z)V+67 javafx.graphics@23.0.1
j javafx.scene.Scene.requestFocus(Ljavafx/scene/Node;Z)V+23 javafx.graphics@23.0.1
j javafx.scene.Node.requestFocus()V+13 javafx.graphics@23.0.1
j hellofx.IMETest$IMEControlSkin.<init>(Lhellofx/IMETest$IMEControl;)V+62
j hellofx.IMETest$IMEControl.createDefaultSkin()Ljavafx/scene/control/Skin;+5
j javafx.scene.control.Control.doProcessCSS()V+25 javafx.controls@23.0.1
j javafx.scene.control.Control$1.doProcessCSS(Ljavafx/scene/Node;)V+4 javafx.controls@23.0.1
j com.sun.javafx.scene.control.ControlHelper.processCSSImpl(Ljavafx/scene/Node;)V+4 javafx.controls@23.0.1
j com.sun.javafx.scene.NodeHelper.processCSS(Ljavafx/scene/Node;)V+5 javafx.graphics@23.0.1
j javafx.scene.Parent.doProcessCSS()V+121 javafx.graphics@23.0.1
j javafx.scene.Parent$1.doProcessCSS(Ljavafx/scene/Node;)V+4 javafx.graphics@23.0.1
j com.sun.javafx.scene.ParentHelper.processCSSImpl(Ljavafx/scene/Node;)V+4 javafx.graphics@23.0.1
j com.sun.javafx.scene.NodeHelper.processCSS(Ljavafx/scene/Node;)V+5 javafx.graphics@23.0.1
j javafx.scene.Node.processCSS()V+99 javafx.graphics@23.0.1
j javafx.scene.Scene.doCSSPass()V+23 javafx.graphics@23.0.1
j javafx.scene.Scene.preferredSize()V+6 javafx.graphics@23.0.1
j javafx.scene.Scene$2.preferredSize(Ljavafx/scene/Scene;)V+1 javafx.graphics@23.0.1
j com.sun.javafx.scene.SceneHelper.preferredSize(Ljavafx/scene/Scene;)V+4 javafx.graphics@23.0.1
j javafx.stage.Window$12.invalidated()V+384 javafx.graphics@23.0.1
j javafx.beans.property.BooleanPropertyBase.markInvalid()V+13 javafx.base@23.0.1
j javafx.beans.property.BooleanPropertyBase.set(Z)V+72 javafx.base@23.0.1
j javafx.stage.Window.setShowing(Z)V+11 javafx.graphics@23.0.1
j javafx.stage.Window.show()V+2 javafx.graphics@23.0.1
j javafx.stage.Stage.show()V+1 javafx.graphics@23.0.1
j hellofx.IMETest.start(Ljavafx/stage/Stage;)V+51
j com.sun.javafx.application.LauncherImpl.lambda$launchApplication1$9(Ljava/util/concurrent/atomic/AtomicBoolean;Ljavafx/application/Application;)V+20 javafx.graphics@23.0.1
j com.sun.javafx.application.LauncherImpl$$Lambda+0x00007f144b092440.run()V+8 javafx.graphics@23.0.1
j com.sun.javafx.application.PlatformImpl.lambda$runAndWait$12(Ljava/lang/Runnable;Ljava/util/concurrent/CountDownLatch;)V+1 javafx.graphics@23.0.1
j com.sun.javafx.application.PlatformImpl$$Lambda+0x00007f144b08e000.run()V+8 javafx.graphics@23.0.1
j com.sun.javafx.application.PlatformImpl.lambda$runLater$10(Ljava/lang/Runnable;)Ljava/lang/Void;+1 javafx.graphics@23.0.1
j com.sun.javafx.application.PlatformImpl$$Lambda+0x00007f144b08f4c0.run()Ljava/lang/Object;+4 javafx.graphics@23.0.1
j java.security.AccessController.executePrivileged(Ljava/security/PrivilegedAction;Ljava/security/AccessControlContext;Ljava/lang/Class;)Ljava/lang/Object;+29 java.base@23.0.1
j java.security.AccessController.doPrivileged(Ljava/security/PrivilegedAction;Ljava/security/AccessControlContext;)Ljava/lang/Object;+13 java.base@23.0.1
j com.sun.javafx.application.PlatformImpl.lambda$runLater$11(Ljava/lang/Runnable;Ljava/security/AccessControlContext;)V+7 javafx.graphics@23.0.1
j com.sun.javafx.application.PlatformImpl$$Lambda+0x00007f144b08e430.run()V+8 javafx.graphics@23.0.1
j com.sun.glass.ui.InvokeLaterDispatcher$Future.run()V+4 javafx.graphics@23.0.1
v ~StubRoutines::call_stub 0x00007f14b3d8ec86
V [libjvm.so+0x8cfb5b] JavaCalls::call_helper(JavaValue*, methodHandle const&, JavaCallArguments*, JavaThread*)+0x2db
V [libjvm.so+0x97c860] jni_invoke_nonstatic(JNIEnv_*, JavaValue*, _jobject*, JNICallType, _jmethodID*, JNI_ArgumentPusher*, JavaThread*) [clone .constprop.1]+0x1d0
V [libjvm.so+0x980068] jni_CallVoidMethodV+0xb8
C [libglassgtk3.so+0x1dda1] JNIEnv_::CallVoidMethod(_jobject*, _jmethodID*, ...)+0x81
C [libglassgtk3.so+0x1ddfc]
Java frames: (J=compiled Java code, j=interpreted, Vv=VM code)
j com.sun.glass.ui.gtk.GtkView.enableInputMethodEventsImpl(JZ)V+0 javafx.graphics@23.0.1
j com.sun.glass.ui.gtk.GtkView._enableInputMethodEvents(JZ)V+3 javafx.graphics@23.0.1
j com.sun.glass.ui.View.enableInputMethodEvents(Z)V+13 javafx.graphics@23.0.1
j com.sun.javafx.tk.quantum.ViewScene.enableInputMethodEvents(Z)V+5 javafx.graphics@23.0.1
j javafx.scene.Scene.enableInputMethodEvents(Z)V+12 javafx.graphics@23.0.1
j javafx.scene.Scene$FocusOwnerProperty.invalidated()V+74 javafx.graphics@23.0.1
j javafx.beans.property.ObjectPropertyBase.markInvalid()V+13 javafx.base@23.0.1
j javafx.beans.property.ObjectPropertyBase.set(Ljava/lang/Object;)V+72 javafx.base@23.0.1
j javafx.scene.Scene.setFocusOwner(Ljavafx/scene/Node;Z)V+67 javafx.graphics@23.0.1
j javafx.scene.Scene.requestFocus(Ljavafx/scene/Node;Z)V+23 javafx.graphics@23.0.1
j javafx.scene.Node.requestFocus()V+13 javafx.graphics@23.0.1
j hellofx.IMETest$IMEControlSkin.<init>(Lhellofx/IMETest$IMEControl;)V+62
j hellofx.IMETest$IMEControl.createDefaultSkin()Ljavafx/scene/control/Skin;+5
j javafx.scene.control.Control.doProcessCSS()V+25 javafx.controls@23.0.1
j javafx.scene.control.Control$1.doProcessCSS(Ljavafx/scene/Node;)V+4 javafx.controls@23.0.1
j com.sun.javafx.scene.control.ControlHelper.processCSSImpl(Ljavafx/scene/Node;)V+4 javafx.controls@23.0.1
j com.sun.javafx.scene.NodeHelper.processCSS(Ljavafx/scene/Node;)V+5 javafx.graphics@23.0.1
j javafx.scene.Parent.doProcessCSS()V+121 javafx.graphics@23.0.1
j javafx.scene.Parent$1.doProcessCSS(Ljavafx/scene/Node;)V+4 javafx.graphics@23.0.1
j com.sun.javafx.scene.ParentHelper.processCSSImpl(Ljavafx/scene/Node;)V+4 javafx.graphics@23.0.1
j com.sun.javafx.scene.NodeHelper.processCSS(Ljavafx/scene/Node;)V+5 javafx.graphics@23.0.1
j javafx.scene.Node.processCSS()V+99 javafx.graphics@23.0.1
j javafx.scene.Scene.doCSSPass()V+23 javafx.graphics@23.0.1
j javafx.scene.Scene.preferredSize()V+6 javafx.graphics@23.0.1
j javafx.scene.Scene$2.preferredSize(Ljavafx/scene/Scene;)V+1 javafx.graphics@23.0.1
j com.sun.javafx.scene.SceneHelper.preferredSize(Ljavafx/scene/Scene;)V+4 javafx.graphics@23.0.1
j javafx.stage.Window$12.invalidated()V+384 javafx.graphics@23.0.1
j javafx.beans.property.BooleanPropertyBase.markInvalid()V+13 javafx.base@23.0.1
j javafx.beans.property.BooleanPropertyBase.set(Z)V+72 javafx.base@23.0.1
j javafx.stage.Window.setShowing(Z)V+11 javafx.graphics@23.0.1
j javafx.stage.Window.show()V+2 javafx.graphics@23.0.1
j javafx.stage.Stage.show()V+1 javafx.graphics@23.0.1
j hellofx.IMETest.start(Ljavafx/stage/Stage;)V+51
j com.sun.javafx.application.LauncherImpl.lambda$launchApplication1$9(Ljava/util/concurrent/atomic/AtomicBoolean;Ljavafx/application/Application;)V+20 javafx.graphics@23.0.1
j com.sun.javafx.application.LauncherImpl$$Lambda+0x00007f144b092440.run()V+8 javafx.graphics@23.0.1
j com.sun.javafx.application.PlatformImpl.lambda$runAndWait$12(Ljava/lang/Runnable;Ljava/util/concurrent/CountDownLatch;)V+1 javafx.graphics@23.0.1
j com.sun.javafx.application.PlatformImpl$$Lambda+0x00007f144b08e000.run()V+8 javafx.graphics@23.0.1
j com.sun.javafx.application.PlatformImpl.lambda$runLater$10(Ljava/lang/Runnable;)Ljava/lang/Void;+1 javafx.graphics@23.0.1
j com.sun.javafx.application.PlatformImpl$$Lambda+0x00007f144b08f4c0.run()Ljava/lang/Object;+4 javafx.graphics@23.0.1
j java.security.AccessController.executePrivileged(Ljava/security/PrivilegedAction;Ljava/security/AccessControlContext;Ljava/lang/Class;)Ljava/lang/Object;+29 java.base@23.0.1
j java.security.AccessController.doPrivileged(Ljava/security/PrivilegedAction;Ljava/security/AccessControlContext;)Ljava/lang/Object;+13 java.base@23.0.1
j com.sun.javafx.application.PlatformImpl.lambda$runLater$11(Ljava/lang/Runnable;Ljava/security/AccessControlContext;)V+7 javafx.graphics@23.0.1
j com.sun.javafx.application.PlatformImpl$$Lambda+0x00007f144b08e430.run()V+8 javafx.graphics@23.0.1
j com.sun.glass.ui.InvokeLaterDispatcher$Future.run()V+4 javafx.graphics@23.0.1
v ~StubRoutines::call_stub 0x00007f14b3d8ec86
j com.sun.glass.ui.gtk.GtkApplication._runLoop(Ljava/lang/Runnable;Z)V+0 javafx.graphics@23.0.1
j com.sun.glass.ui.gtk.GtkApplication.lambda$runLoop$10(Ljava/lang/Runnable;Z)V+7 javafx.graphics@23.0.1
j com.sun.glass.ui.gtk.GtkApplication$$Lambda+0x00007f144b032bb8.run()V+12 javafx.graphics@23.0.1
j java.lang.Thread.runWith(Ljava/lang/Object;Ljava/lang/Runnable;)V+5 java.base@23.0.1
j java.lang.Thread.run()V+19 java.base@23.0.1
v ~StubRoutines::call_stub 0x00007f14b3d8ec86