Shortest Remaining Time First scheduling algorithm

Shortest Remaining Time First scheduling algorithm is Really Versatile Solution?

The shortest remaining time first is a scheduling algorithm of an operating system Shortest Remaining Time First (SRTF).

Shortest Remaining Time The First scheduling algorithm is mostly preemptive of SJF scheduling. In shortest time remaining time first scheduling algorithm the execution process stopped after some certain time immediately.

When all the process is done or in ready to queue to work, then It will not run like a preemptive, It is work as SJF scheduling algorithm. In the shortest remaining time, the first scheduling algorithm the process control block system feature is awesome and useful. because it is accessible to the next execution of the process.

Shortest Remaining Time First Scheduling Criteria

  • The process that requires the shortest time to complete execution, is served first. 

Shortest Remaining Time First Scheduling Decision Mode

  • preemptive: When a new process arrives, its total time is compared to the current process remaining time.
  • If the new job needs less time to finish than the current process, the current process is suspended and the new job started.

Shortest Remaining Time First Scheduling Implementation

  • This strategy can be easily implemented by using FIFO. FIFO means First In First Out.
  • Firstly select that process which arrives and then completes it to the 1 unit of time after that
  • Check for the shortest remaining time from the arrival process only.
  • Similarly, All the processes get the execution.
  • Firstly for Finding Completion time, looking in the Gantt chart from the back and complete of each process is completion time.
  • Secondly, Turn Around Time = Completion Time – Arrival Time.
  • Thirdly, Waiting Time = Turn Around Time – Burst Time.

Also Read –> Priority-Based Scheduling Algorithm

For Example

Process Arrival Time (A.T.) Burst Time (B.T.)
P0 0 10
P1 1 6
P2 3 2
P3 5 4

That is to say, 

  • Only one process is arriving at 0 time P0. so, we have to do the execution of process P0 for 1 unit time.
  • After that First process is getting the executes the first-time check for the shortest remaining time of arrived processes.
  • Similarly, All the processes execute likewise.

As a result, we get

Gantt Chart

shortest remaining time first

Table

Process Arrival Time Burst Time Completion Time Turnaround Time Waiting Time
P0 0 10 22 22 12
P1 1 6 9 8 2
P2 3 2 5 2 0
P3 5 4 13 8 4

Average Turnaround Time:(22+8+2+8)/4 = 10.0

Average Waiting Time: (12+2+0+4)/4 = 4.5

Throughput: 0.181818

Advantages

  • It is optimal and guarantees Less waiting time during programming.
  • In the shortest remaining time first scheduling algorithm the Response time is less.
  • It provides standard and It is better than other all algorithm and that’s why It called the versatile scheduling algorithm.

Disadvantages

  • We can’t predict the completion time of the process.
  • Starvation is possible for a long process.
  • Priority can’t be set for the processes.
  • If processes have large burst time then It performs poor response time.
  • It leads to starvation when It comes to the large burst time.

Comment for any query.
To learn more concept about SRTF go to 
https://www.geeksforgeeks.org/program-shortest-job-first-scheduling-set-2srtf-make-changesdoneplease-review/

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