CPU Scheduler Simulation

This project implements a multithreaded CPU scheduling simulator in C. It demonstrates how different scheduling policies affect turnaround time, waiting time, and execution order of processes.

Features

• Multithreaded simulation single core

  • Arrival Thread – simulates process arrivals.
  • Scheduler Thread – selects processes for CPU execution.
  • Wakeup Thread – handles I/O-completed processes returning to the ready queue.

• Supported Scheduling Algorithms

  • First Come First Serve (FCFS) – Non-preemptive, processes run in arrival order.
  • Shortest Job First (SJF) – Non-preemptive, picks process with shortest burst time.
  • Shortest Remaining Time First (SRTF) – Preemptive, dynamically selects process with least remaining burst.
  • Round Robin (RR) – Preemptive, each process runs for a fixed time quantum before requeue.

• Metrics Collected

  • Average turnaround time
  • Maximum completion time
  • Simulator run time

Requirements

• GCC / Clang
• GNU Make
• pthread library (POSIX threads)

Tested on

• gcc version 15.2.1 (GCC)
• GNU Make 4.4.1
• Fedora 42

Build & Run

git clone <repo_url>
cd cpu_scheduler
make
./main <input_file> <algorithm>

Example:

./main test_cases/process1.dat rr 

Output

The simulator prints:

• Console Output

  • Turnaround time for each process
  • Waiting time for each process
  • Average turnaround and waiting times per scheduling policy

• Log File

  • Timeline of CPU execution
  • Which process ran, at what time, and for how long
  • Context switch points (when preemption or quantum expiry occurs)

CPU0
<process_name>,<cpu_id>    <start_time>    <end_time>
p0,1    40    55
p1,1    55    105
p2,1    105    120
p3,1    120    172

Limitations

• Currently supports only a single CPU core.
• I/O support is limited.
• Memory management is minimal (possible leaks).
• Code can be refactored for cleaner design and extensibility.

License

MIT License – feel free to modify and use.