When restart()ing a ScheduledService while having assertions enabled, the assertions in [1] or [2] fail. Without assertions the code seems to run fine, though.
According to the inline comments, "resetting things should have cleared the delayTask". Therefore I wonder, if resetting the delayTask is missing in reset(). At the moment this field is only set to null during cancel() [3] as well as after exception-free execution of a previous TimerTask [4]. A workaround would be to call cancel() first, but one has to make sure to be in a valid state. I wonder if there is some documentation about the state transitions and how to start, stop and restart a service correctly. [1]: https://github.com/openjdk/jfx/blob/e98645932d0d7765988f21b09d6d121202281e02/modules/javafx.graphics/src/main/java/javafx/concurrent/ScheduledService.java#L357 <https://github.com/openjdk/jfx/blob/e98645932d0d7765988f21b09d6d121202281e02/modules/javafx.graphics/src/main/java/javafx/concurrent/ScheduledService.java#L357> [2]: https://github.com/openjdk/jfx/blob/e98645932d0d7765988f21b09d6d121202281e02/modules/javafx.graphics/src/main/java/javafx/concurrent/ScheduledService.java#L379 <https://github.com/openjdk/jfx/blob/e98645932d0d7765988f21b09d6d121202281e02/modules/javafx.graphics/src/main/java/javafx/concurrent/ScheduledService.java#L379> [3]: https://github.com/openjdk/jfx/blob/e98645932d0d7765988f21b09d6d121202281e02/modules/javafx.graphics/src/main/java/javafx/concurrent/ScheduledService.java#L469 <https://github.com/openjdk/jfx/blob/e98645932d0d7765988f21b09d6d121202281e02/modules/javafx.graphics/src/main/java/javafx/concurrent/ScheduledService.java#L469> [4]: https://github.com/openjdk/jfx/blob/e98645932d0d7765988f21b09d6d121202281e02/modules/javafx.graphics/src/main/java/javafx/concurrent/ScheduledService.java#L524 <https://github.com/openjdk/jfx/blob/e98645932d0d7765988f21b09d6d121202281e02/modules/javafx.graphics/src/main/java/javafx/concurrent/ScheduledService.java#L524>
