Better api for recurring tasks with persistent schedule (having multiple instances)

[kagkarlsson]

Adding a bit better support for recurring tasks that can have many instances with variable schedule. Feedback is appreciated.

After requests/discussions in among others

• Is there a way to schedule a recurring task on the fly? #246
• ..?

Current example:

    @Override
    public void run(DataSource dataSource) {

        final RecurringTaskWithPersistentSchedule<SerializableCronSchedule> task =
            Tasks.recurringWithPersistentSchedule("dynamic-recurring-task", SerializableCronSchedule.class)
                .execute((taskInstance, executionContext) -> {
                    System.out.println("Instance: '" + taskInstance.getId() + "' ran using persistent schedule: " + taskInstance.getData().getSchedule());
                });

        final Scheduler scheduler = Scheduler
            .create(dataSource, task)
            .pollingInterval(Duration.ofSeconds(1))
            .registerShutdownHook()
            .build();

        scheduler.start();
        sleep(2_000);

        scheduler.schedule(task.schedulableInstance("id1", new SerializableCronSchedule("0/6 * * * * ?")));
        scheduler.schedule(task.schedulableInstance("id2", new SerializableCronSchedule("3/6 * * * * ?")));
    }

Resulting in

17:45:22.258 INFO  com.github.kagkarlsson.scheduler.Scheduler - Starting scheduler.
Instance: 'id2' ran using persistent schedule: CronSchedule pattern=3/6 * * * * ?, zone=Europe/Oslo
Instance: 'id1' ran using persistent schedule: CronSchedule pattern=0/6 * * * * ?, zone=Europe/Oslo
Instance: 'id2' ran using persistent schedule: CronSchedule pattern=3/6 * * * * ?, zone=Europe/Oslo
Instance: 'id1' ran using persistent schedule: CronSchedule pattern=0/6 * * * * ?, zone=Europe/Oslo
Instance: 'id2' ran using persistent schedule: CronSchedule pattern=3/6 * * * * ?, zone=Europe/Oslo