SegmentReadTaskScheduler waste too many CPU

[JinheLin]

Bug Report

The reason is that:

• scheduleSegmentReadTaskPoolUnlock does not check the limit on the number of active segments. If the number of active segments has reached the limit, this causes scheduleSegmentUnlock to fail to schedule a segment.
• When scheduleSegmentUnlock scheduling fails, the scheduler will immediately execute the next scheduling because there may be other segmentReadTaskPools to schedule.
• If there are no tasks to schedule, this will cause the scheduling to keep executing between scheduleSegmentReadTaskPoolUnlock and scheduleSegmentUnlock.