update pss.java

src/main/java/com/thealgorithms/scheduling/pss.java

@@ -0,0 +1,136 @@
+package com.thealgorithms.scheduling;
+
+import java.util.ArrayList;
+import java.util.Comparator;
+import java.util.List;
+import java.util.PriorityQueue;
+
+/**
+ * The Proportional Share Scheduling (PSS) class implements a dynamic scheduling algorithm.
+ * It assigns the CPU to processes based on their weight, ensuring that each process gets CPU time proportional to its weight.
+ * The priority boost prevents starvation, ensuring that lower-weight processes still receive CPU time.
+ */
+public final class ProportionalShareScheduling {
+
+    private ProportionalShareScheduling() {
+    }
+
+    private List<Process> processes;
+
+    /**
+     * Constructs a ProportionalShareScheduling object with a list of processes.
+     *
+     * @param processes List of processes to be scheduled.
+     */
+    public ProportionalShareScheduling(final List<Process> processes) {
+        this.processes = processes;
+    }
+
+    /**
+     * Schedules the processes using Proportional Share Scheduling (PSS).
+     * Processes are scheduled based on their weight and priority boost.
+     * It simulates their execution, calculates the waiting time, and ensures no starvation.
+     *
+     * @return List of processes after they have been executed in proportion to their weight.
+     */
+    public List<Process> scheduleProcesses(int totalTimeQuantum) {
+        PriorityQueue<Process> readyQueue = new PriorityQueue<>(new ProcessComparator());
+        readyQueue.addAll(processes);
+        int currentTime = 0;
+        List<Process> executedProcesses = new ArrayList<>();
+
+        while (!readyQueue.isEmpty()) {
+            Process current = readyQueue.poll();
+
+            // Determine time quantum to allocate to the current process
+            int timeGiven = Math.min(current.getWeight(), current.getBurstTime() - current.getTimeReceived());
+            currentTime += timeGiven;
+            current.setTimeReceived(current.getTimeReceived() + timeGiven);
+
+            System.out.println("Process " + current.getProcessId() + " received " + timeGiven + " units at time " + currentTime);
+
+            // If the process has finished execution
+            if (current.getTimeReceived() >= current.getBurstTime()) {
+                System.out.println("Process " + current.getProcessId() + " completed at time " + currentTime);
+            } else {
+                // Starvation prevention: increase priority boost for unfinished processes
+                current.setPriorityBoost(current.getPriorityBoost() + 1);
+                readyQueue.add(current); // Reinsert into the queue for future execution
+            }
+
+            // Starvation prevention logic for all other processes in the queue
+            for (Process p : readyQueue) {
+                p.setPriorityBoost(p.getPriorityBoost() + 1); // Increase the boost to prevent starvation
+            }
+
+            executedProcesses.add(current);
+        }
+
+        return executedProcesses;
+    }
+
+    /**
+     * The Process class represents a process with an ID, weight, burst time, arrival time, time received, and priority boost.
+     */
+    public static class Process {
+        private String processId;
+        private int weight;
+        private int burstTime;
+        private int arrivalTime;
+        private int timeReceived;
+        private int priorityBoost;
+
+        public Process(String processId, int weight, int burstTime, int arrivalTime) {
+            this.processId = processId;
+            this.weight = weight;
+            this.burstTime = burstTime;
+            this.arrivalTime = arrivalTime;
+            this.timeReceived = 0;
+            this.priorityBoost = 0;
+        }
+
+        public String getProcessId() {
+            return processId;
+        }
+
+        public int getWeight() {
+            return weight;
+        }
+
+        public int getBurstTime() {
+            return burstTime;
+        }
+
+        public int getArrivalTime() {
+            return arrivalTime;
+        }
+
+        public int getTimeReceived() {
+            return timeReceived;
+        }
+
+        public void setTimeReceived(int timeReceived) {
+            this.timeReceived = timeReceived;
+        }
+
+        public int getPriorityBoost() {
+            return priorityBoost;
+        }
+
+        public void setPriorityBoost(int priorityBoost) {
+            this.priorityBoost = priorityBoost;
+        }
+    }
+
+    /**
+     * The ProcessComparator class compares processes based on their effective weight (weight + priority boost).
+     */
+    public static class ProcessComparator implements Comparator<Process> {
+        @Override
+        public int compare(Process p1, Process p2) {
+            int effectiveWeight1 = p1.getWeight() + p1.getPriorityBoost();
+            int effectiveWeight2 = p2.getWeight() + p2.getPriorityBoost();
+            return Integer.compare(effectiveWeight2, effectiveWeight1); // Higher weight gets higher priority
+        }
+    }
+}