public Disposable observeForever(final Consumer<WorkerTaskEvent<I, P, R>> observer) {
        return taskEventData.subscribe(event -> {
            synchronized (taskMutex) {
                postToListener(event, observer);
            }
        });
    }
registers an observer not bound to a lifecycle. This method is used for Unit-Tests
main/src/main/java/cgeo/geocaching/utils/workertask/WorkerTask.java