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Cron scheduling

One-off delays (after, at) and retries are built into the core — see getting started. For recurring work there is mc-task-queue-schedule: cron-style TaskSchedule definitions in their own store, where every firing becomes an ordinary TaskSubmission.

<dependency>
  <groupId>ai.mindconnect</groupId>
  <artifactId>mc-task-queue-schedule</artifactId>
  <version>0.5.0</version>
</dependency>

Defining and running schedules​

var scheduler = new TaskScheduler(queue, new InMemoryScheduleStore());
scheduler.schedule(TaskSchedule.of("nightly-report", "report", "0 0 3 * * *", payload)
        .named("Nightly report")
        .in(ZoneId.of("Europe/Berlin"))
        .withMaxAttempts(3));
scheduler.start();

TaskSchedule parses its cron eagerly (a typo fails at definition time, not at 3 a.m.) and carries priority / maxAttempts forward into each submission. The scheduler sleeps until the next firing (withMaxSleep caps the nap); tick() and a steerable Clock make it testable without waiting.

Safe on every node​

There is no leader election: the scheduler can run on every node, because firing is a compare-and-set on the store — ScheduleStore.claimFiring(id, firedFor) lets exactly one node win each occurrence; the others simply move on. recordFired(id, taskId) links the schedule to the task it produced.

Store implementations

Only InMemoryScheduleStore ships today. The Postgres DDL for a schedule store exists in mc-task-queue-jdbc, but the JdbcScheduleStore itself is not implemented yet — durable schedules need your own ScheduleStore.

Cron syntax​

CronExpression is hand-written and dependency-free:

  • 5 fields (min hour dom mon dow) or 6 (seconds first);
  • names (MON, JAN), ranges, steps and lists (1-5, */15, 1,15), ?;
  • shortcuts @hourly, @daily / @midnight, @weekly, @monthly, @yearly;
  • day-of-month OR day-of-week semantics (like classic cron), DST handled by java.time.