Shortest Remaining Time First (SRTF) Scheduling Algorithm: Minimizing Average Waiting Time Through Preemptive Scheduling

Understand the Shortest Remaining Time First (SRTF) scheduling algorithm and its effectiveness in minimizing average process waiting times. This tutorial provides a detailed explanation of SRTF's operation, a step-by-step example with calculations, and a visual Gantt chart for improved comprehension.

Shortest Remaining Time First (SRTF) Scheduling Algorithm

Understanding SRTF Scheduling

The Shortest Remaining Time First (SRTF) algorithm is a preemptive scheduling algorithm that aims to minimize the average waiting time for processes. It's a variation of the Shortest Job First (SJF) algorithm, but unlike SJF (which is non-preemptive), SRTF can interrupt (preempt) a currently running process if a new process with a shorter remaining burst time arrives. This makes it more responsive than SJF but adds scheduling overhead.

How SRTF Works

SRTF works by selecting the process with the shortest remaining burst time (the time needed to complete execution) from the ready queue. When a new process arrives, the scheduler compares its burst time to the remaining burst time of the currently running process. If the new process has a shorter remaining burst time, the current process is preempted, and the new process is scheduled. The preempted process is placed back into the ready queue and will be scheduled again later. Once all processes have arrived, SRTF behaves like SJF (Shortest Job First), scheduling the shortest remaining job until all jobs are complete.

Example: SRTF Scheduling

Let's consider six processes (P1-P6) with the following arrival and burst times:

Average Waiting Time = 24/6 = 4ms