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Add Round Robin scheduling (#4184)
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99
src/main/java/com/thealgorithms/scheduling/RRScheduling.java
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99
src/main/java/com/thealgorithms/scheduling/RRScheduling.java
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/**
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* @author Md Asif Joardar
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*/
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package com.thealgorithms.scheduling;
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import com.thealgorithms.devutils.entities.ProcessDetails;
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import java.util.Arrays;
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import java.util.LinkedList;
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import java.util.List;
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import java.util.Queue;
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/**
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* The Round-robin scheduling algorithm is a kind of preemptive First come, First Serve CPU Scheduling algorithm.
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* This can be understood here - https://www.scaler.com/topics/round-robin-scheduling-in-os/
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*/
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public class RRScheduling {
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private List<ProcessDetails> processes;
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private int quantumTime;
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RRScheduling(final List<ProcessDetails> processes, int quantumTime) {
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this.processes = processes;
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this.quantumTime = quantumTime;
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}
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public void scheduleProcesses() {
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evaluateTurnAroundTime();
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evaluateWaitingTime();
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}
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private void evaluateTurnAroundTime() {
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int processesNumber = processes.size();
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if(processesNumber == 0) {
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return;
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}
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Queue<Integer> queue = new LinkedList<>();
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queue.add(0);
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int currentTime = 0; // keep track of the time
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int completed = 0;
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int[] mark = new int[processesNumber];
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Arrays.fill(mark, 0);
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mark[0] = 1;
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// a copy of burst time to store the remaining burst time
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int[] remainingBurstTime = new int[processesNumber];
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for (int i = 0; i < processesNumber; i++) {
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remainingBurstTime[i] = processes.get(i).getBurstTime();
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}
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while (completed != processesNumber){
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int index = queue.poll();
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if(remainingBurstTime[index] == processes.get(index).getBurstTime()){
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currentTime = Math.max(currentTime, processes.get(index).getArrivalTime());
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}
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if(remainingBurstTime[index] - quantumTime > 0){
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remainingBurstTime[index] -= quantumTime;
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currentTime += quantumTime;
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} else {
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currentTime += remainingBurstTime[index];
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processes.get(index).setTurnAroundTimeTime(currentTime - processes.get(index).getArrivalTime());
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completed++;
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remainingBurstTime[index]=0;
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}
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// If some process has arrived when this process was executing, insert them into the queue.
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for (int i=1; i < processesNumber; i++){
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if(remainingBurstTime[i] > 0 && processes.get(i).getArrivalTime() <= currentTime && mark[i] == 0){
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mark[i]=1;
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queue.add(i);
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}
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}
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// If the current process has burst time remaining, push the process into the queue again.
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if(remainingBurstTime[index] > 0) queue.add(index);
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// If the queue is empty, pick the first process from the list that is not completed.
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if(queue.isEmpty()){
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for (int i=1; i<processesNumber; i++){
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if (remainingBurstTime[i] > 0){
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mark[i] = 1;
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queue.add(i);
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break;
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}
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}
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}
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}
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}
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private void evaluateWaitingTime() {
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for (int i = 0; i < processes.size(); i++)
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processes.get(i).setWaitingTime(processes.get(i).getTurnAroundTimeTime() - processes.get(i).getBurstTime());
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}
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}
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