SRTF

SRTF, or Shortest Remaining Time First, is a preemptive CPU scheduling algorithm used in operating systems. It is the preemptive variant of the Shortest Job First strategy. The scheduler always runs the ready process with the smallest remaining CPU burst time. If a new process arrives whose total burst time is shorter than the remaining time of the currently running process, the current process is preempted and the new process begins execution.

Implementation typically uses a priority queue or min-heap keyed by remaining burst time. Each arrival or completion can trigger a preemption decision. Because the algorithm relies on knowledge of remaining times, it assumes either exact burst lengths or estimates. In practice, remaining times are often updated using historical data or exponential averaging to provide forecasts.

Advantages of SRTF include reduced average waiting time (and often reduced turnaround time) for workloads with a mix of short and long processes, and improved responsiveness for short tasks in interactive systems. It is particularly effective when short jobs arrive frequently.

Disadvantages include potential starvation of long processes if many short jobs keep arriving, as well as the overhead from frequent preemptions and context switches. The algorithm also depends on accurate or reliable burst-time estimates, which may not always be available.

Relation to other schedulers: SRTF is the preemptive counterpart to SJF. Unlike non-preemptive SJF, SRTF can interrupt a running process to start a shorter one, which can improve short-job performance but increase scheduling complexity and overhead.

Notes: SRTF is commonly discussed in scheduling theory and education. In practical systems, exact burst times are rarely known, so variants use estimates, making the behavior approximate rather than exact.