@Override
    protected void destroyContext() {
        synchronized (lock) {
            canvas.destroy();
        }

        // request the cleanup
        signalTerminate.release();
        super.destroyContext();
    }
(non-Javadoc)
@see com.jme3.system.lwjgl.LwjglWindow#destroyContext()
jme3-lwjgl3/src/main/java/com/jme3/system/lwjgl/LwjglCanvas.java