A DESCRIPTION OF THE PROBLEM :
Unhandled exception in Toolkit.getToolkit().startup() causes Platform.runLater() to hang forever. This happens, for example, on headless Linux machines.
Stack traces and thread dumps can be found here https://github.com/ylexus/jiotty-photos-uploader/issues/115.


STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :

To reproduce, run a javafx program on a headless Linux box.
1. Call Application.lanuch()
2. Call Platform.runLater() from another thread - it will block waiting on a CountdownLatch for Platform to fully start
3. PlatformImpl.startup() calls
Toolkit.getToolkit().startup(() -> {
            startupLatch.countDown();
            r.run();
        });
4. Toolkit fails before it invokes the runnable:
2021-06-24T22:09:53,774 ERROR [Thread-2] j.l.Throwable Exception in thread "Thread-2" java.lang.UnsupportedOperationException: Unable to open DISPLAY
2021-06-24T22:09:53,776 ERROR [Thread-2] j.l.Throwable at javafx.graphics/com.sun.glass.ui.gtk.GtkApplication.lambda$new$6(GtkApplication.java:173)
2021-06-24T22:09:53,777 ERROR [Thread-2] j.l.Throwable at java.base/java.security.AccessController.doPrivileged(AccessController.java:312)
2021-06-24T22:09:53,778 ERROR [Thread-2] j.l.Throwable at javafx.graphics/com.sun.glass.ui.gtk.GtkApplication.<init>(GtkApplication.java:171)
2021-06-24T22:09:53,779 ERROR [Thread-2] j.l.Throwable at javafx.graphics/com.sun.glass.ui.gtk.GtkPlatformFactory.createApplication(GtkPlatformFactory.java:41)
2021-06-24T22:09:53,779 ERROR [Thread-2] j.l.Throwable at javafx.graphics/com.sun.glass.ui.Application.run(Application.java:145)
2021-06-24T22:09:53,780 ERROR [Thread-2] j.l.Throwable at javafx.graphics/com.sun.javafx.tk.quantum.QuantumToolkit.startup(QuantumToolkit.java:281)
2021-06-24T22:09:53,781 ERROR [Thread-2] j.l.Throwable at javafx.graphics/com.sun.javafx.application.PlatformImpl.startup(PlatformImpl.java:288)
2021-06-24T22:09:53,782 ERROR [Thread-2] j.l.Throwable at javafx.graphics/com.sun.javafx.application.PlatformImpl.startup(PlatformImpl.java:160)
2021-06-24T22:09:53,783 ERROR [Thread-2] j.l.Throwable at javafx.graphics/com.sun.javafx.application.LauncherImpl.startToolkit(LauncherImpl.java:658)
2021-06-24T22:09:53,784 ERROR [Thread-2] j.l.Throwable at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplication1(LauncherImpl.java:678)
2021-06-24T22:09:53,785 ERROR [Thread-2] j.l.Throwable at javafx.graphics/com.sun.javafx.application.LauncherImpl.lambda$launchApplication$2(LauncherImpl.java:195)
2021-06-24T22:09:53,785 ERROR [Thread-2] j.l.Throwable at java.base/java.lang.Thread.run(Thread.java:831)

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Platform.runLater() returns
ACTUAL -
Result: the thread that called Platform.runLater() is blocked forever.

---------- BEGIN SOURCE ----------
On a headless Linux box, follow instructions on https://github.com/ylexus/jiotty-photos-uploader to run the GUI.
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Be careful not to invoke Platform.runLater() before the platform is fully initialised.

FREQUENCY : always