I've an assignment to implementing a specific process-scheduling algorithm and simulating its behavior in a multiprogramming environment. It aims to demonstrate the performance of the scheduling algorithm in terms of CPU utilization, average turnaround time, and average waiting time.
import java.util.*;public class Scheduler { private List<Process> processes; private int currentTime = 0; private List<String> ganttChart = new ArrayList<>(); private int contextSwitches = 0; private int totalIdleTime = 0; public Scheduler(List<Process> processes) { this.processes = new ArrayList<>(processes); this.processes.sort((a, b) -> a.arrivalTime - b.arrivalTime); } public void run() { List<Process> readyQueue = new ArrayList<>(); int index = 0; Process currentProcess = null; while (index < processes.size() || !readyQueue.isEmpty() || currentProcess != null) { // Add arriving processes to the ready queue while (index < processes.size() && processes.get(index).arrivalTime <= currentTime) { readyQueue.add(processes.get(index)); index++; } // Find the process with the shortest remaining time Process nextProcess = getShortestRemainingTimeProcess(readyQueue); // If the next process is different from the currently running process, preempt if (currentProcess != null && nextProcess != null && nextProcess.id != currentProcess.id) { ganttChart.add("CS"); // Context switch contextSwitches++; currentTime++; // Context switch takes 1 ms } // If no process is running, pick the next one from the ready queue if (currentProcess == null || (nextProcess != null && nextProcess.id != currentProcess.id)) { currentProcess = nextProcess; if (currentProcess != null && currentProcess.responseTime == -1) { currentProcess.responseTime = currentTime - currentProcess.arrivalTime; } } // If a process is running, execute it if (currentProcess != null) { ganttChart.add("P" + currentProcess.id); currentProcess.remainingTime--; // If the process completes, mark its completion time if (currentProcess.remainingTime == 0) { currentProcess.completionTime = currentTime + 1; currentProcess = null; } } else { // If no process is running, the CPU is idle ganttChart.add("Idle"); totalIdleTime++; } currentTime++; } } // Helper method to find the process with the shortest remaining time private Process getShortestRemainingTimeProcess(List<Process> readyQueue) { if (readyQueue.isEmpty()) { return null; } Process shortestProcess = readyQueue.get(0); for (Process p : readyQueue) { if (p.remainingTime < shortestProcess.remainingTime || (p.remainingTime == shortestProcess.remainingTime && p.arrivalTime < shortestProcess.arrivalTime)) { shortestProcess = p; } } readyQueue.remove(shortestProcess); return shortestProcess; } public void printResults() { int totalTurnaround = 0, totalWaiting = 0; for (Process p : processes) { p.turnaroundTime = p.completionTime - p.arrivalTime; p.waitingTime = p.turnaroundTime - p.burstTime; totalTurnaround += p.turnaroundTime; totalWaiting += p.waitingTime; } double avgTurnaround = (double) totalTurnaround / processes.size(); double avgWaiting = (double) totalWaiting / processes.size(); double cpuUtil = ((currentTime - totalIdleTime) / (double) currentTime) * 100; System.out.println("Time Process"); int start = 0; for (int i = 0; i < ganttChart.size(); i++) { if (i > 0 && !ganttChart.get(i).equals(ganttChart.get(i - 1))) { System.out.printf("%d-%d %s\n", start, i, ganttChart.get(i - 1)); start = i; } } System.out.printf("%d-%d %s\n\n", start, ganttChart.size(), ganttChart.get(ganttChart.size() - 1)); System.out.printf("Average Turnaround Time: %.2f\n", avgTurnaround); System.out.printf("Average Waiting Time: %.2f\n", avgWaiting); System.out.printf("CPU Utilization: %.2f%%\n", cpuUtil); }}This is my Process class
import java.util.*;public class Process { int id; int arrivalTime; int burstTime; int remainingTime; int completionTime; int turnaroundTime; int waitingTime; int responseTime = -1; public Process(int id, int arrivalTime, int burstTime) { this.id = id; this.arrivalTime = arrivalTime; this.burstTime = burstTime; this.remainingTime = burstTime; }}And this is the main:
import java.util.*;public class Main { public static void main(String[] args) { Scanner scanner = new Scanner(System.in); System.out.print("Enter number of processes: "); int n = scanner.nextInt(); List<Process> processes = new ArrayList<>(); for (int i = 0; i < n; i++) { System.out.print("Enter arrival time and burst time for process P" + (i + 1) +": "); int arrival = scanner.nextInt(); int burst = scanner.nextInt(); processes.add(new Process(i + 1, arrival, burst)); } Scheduler scheduler = new Scheduler(processes); scheduler.run(); scheduler.printResults(); }}It should be using shortest remaining time first (Preemptive SJF), using first come first serve.
Expected output:
Number of processes= 4 (P1, P2, P3, P4)Arrival times and burst times as follows:P1: Arrival time = 0, Burst time = 8 msP2: Arrival time = 1, Burst time = 4 msP3: Arrival time = 2, Burst time = 5 msP4: Arrival time = 3, Burst time = 5 msScheduling Algorithm: Shortest remaining time firstContext Switch: 1 msTime Process/CS0-1 P11-2 CS2-6 P26-7 CS7-12 P312-13 CS13-18 P418-19 CS19-26 P1Performance MetricsAverage Turnaround Time: 14Average Waiting Time: 8.5CPU Utilization: 84.62Actual output:
Number of processes= 4 (P1, P2, P3, P4)Arrival times and burst times as follows:P1: Arrival time = 0, Burst time = 8 msP2: Arrival time = 1, Burst time = 4 msP3: Arrival time = 2, Burst time = 5 msP4: Arrival time = 3, Burst time = 5 msScheduling Algorithm: Shortest remaining time firstContext Switch: 1 msTime Process/CS0-8 P18-9 CS9-13 P213-14 CS14-19 P319-20 CS20-25 P425-26 idlePerformance MetricsAverage Turnaround Time: 14.75Average Waiting Time: 9.25CPU Utilization: 88.46%What is the problem?