EDF Scheduler

Introduction

The EDF scheduler is the initial scheduler provided by Folia, and the default. This scheduler is part of the ConcurrentUtil library by SpottedLeaf.

This scheduler has been in Folia the longest, and was the first scheduler used in Folia. This is also the stablest option of all the schedulers provided in this documentation, given its long run of testing proving it to be reliable.

To set your scheduler to EDF, change the threaded-regions.scheduler option in paper-global.yml to EDF

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What is “EDF”?

EDF stands for Earliest-Deadline-First, which is a CPU scheduling algorithm that assigns priorities to tasks according to the absolute deadline(in this case, nanoseconds). The task whose deadline is first gets the highest priority. This is pretty consistent throughout all the schedulers though. This scheduler attempts to ensure all task deadlines are met by making it so that each time a tick runner finishes a task, it will request a new one under the scheduling lock.

This scheduler, by nature, does not guarantee any task will remain on the same thread for more than 1 tick. By design, the soonest task will be picked up by the tick runner that is next available, to ensure the deadline is met. Tasks can be picked up at the end of the tick of another task, or if a new task is inserted, and there are idle runners. If there is an idle runner during task insertion, the task gets accepted by the first idle runner immediately.

It’s the least performant of all the options listed, however it is the most stable and reliable.

Technical details

All operations involving the queue of the scheduler, like insertion, polling, etc, run through a lock called the scheduleLock. This lock ensures all operations are atomic and safe, and avoids race conditions and such.

The tasks are compared via a comparator of their tick times, always choosing the task with the sooner deadline. The tie breaker is defined by Long.signum(task1.id - task2.id). The ids are unique per task