Operating System

Explain about shortest-job-first (SJF) CPU scheduling .

Shortest Job First (SJF) CPU scheduling is a policy that prioritizes processes with the shortest execution time to execute next. It’s also known as Shortest Job Next (SJN). SJF can be preemptive or non-preemptive. 

SJF has the following advantages:

  • Minimizes waiting times
  • Ensures short tasks are executed quickly:
  • Optimal average turnaround time
  • Optimal for batch processes where burst time is known beforehand 

However, SJF can cause starvation if shorter processes keep coming. This is called starvation, where a shorter process has to wait for a long time until the current longer process gets executed. This problem can be solved using the concept of aging. 

SJF is a greedy algorithm that has the advantage of having a minimum average waiting time among all scheduling algorithms. 

SJF is used in many real-life scenarios, such as online delivery apps, which always choose to deliver the nearest order first, then after delivering the first order, it searches for the next nearest delivery location.

Shortest Job First (SJF) is a non-preemptive CPU scheduling algorithm that prioritizes processes with the shortest execution times. Here’s an example of how SJF works:

  • Sort all processes by arrival time
  • Choose the process with the shortest arrival and burst time
  • Execute the current process
  • Push all waiting processes into a queue
  • When the current process ends, choose the process with the shortest burst time from the waiting processes 

SJF has the following advantages: Maximum throughput and Minimum average waiting and turnaround time. 

However, SJF may cause starvation if shorter processes keep coming. This problem can be solved using the concept of aging. 

Here’s an example of SJF in action:

  • Process P3 arrives
  • However, P4 still needs 2 execution units to complete
  • Thus, P3 will wait till P4 gets executed 

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