Skip dispatching extend_acquired_job_leases with no jobs (#1031)

Author: JacobHayes

docs/versionhistory.rst

@@ -64,6 +64,7 @@ APScheduler, see the :doc:`migration section <migration>`.
   schema if it's missing (PR by @zhu0629)
 - Fixed an issue with ``CronTrigger`` infinitely looping to get next date when DST ends
   (`#980 <https://github.com/agronholm/apscheduler/issues/980>`_; PR by @hlobit)
+- Skip dispatching extend_acquired_job_leases with no jobs (PR by @JacobHayes)
 
 **4.0.0a5**
 

src/apscheduler/_schedulers/async_.py

@@ -1108,10 +1108,10 @@ async def check_queue_capacity(event: Event) -> None:
         async def extend_job_leases() -> None:
             while self._state is RunState.started:
                 await sleep(self.lease_duration.total_seconds() / 2)
-                job_ids = {job.id for job in self._running_jobs}
-                await self.data_store.extend_acquired_job_leases(
-                    self.identity, job_ids, self.lease_duration
-                )
+                if job_ids := {job.id for job in self._running_jobs}:
+                    await self.data_store.extend_acquired_job_leases(
+                        self.identity, job_ids, self.lease_duration
+                    )
 
         async with AsyncExitStack() as exit_stack:
             # Start the job executors