Add MLFQScheduler.java new algorithm

Author: Hardvan

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

@@ -0,0 +1,146 @@
+package com.thealgorithms.scheduling;
+
+import java.util.LinkedList;
+import java.util.Queue;
+
+/**
+ * The Multi-Level Feedback Queue (MLFQ) Scheduler class.
+ * This class simulates scheduling using multiple queues, where processes move
+ * between queues depending on their CPU burst behavior.
+ */
+public class MLFQScheduler {
+    private Queue<Process>[] queues; // Multi-level feedback queues
+    private int timeQuantum[]; // Time quantum for each queue level
+    private int currentTime; // Current time in the system
+
+    /**
+     * Constructor to initialize the MLFQ scheduler with the specified number of
+     * levels
+     * and their corresponding time quantums.
+     *
+     * @param levels       Number of queues (priority levels)
+     * @param timeQuantums Time quantum for each queue level
+     */
+    public MLFQScheduler(int levels, int[] timeQuantums) {
+        queues = new LinkedList[levels];
+        for (int i = 0; i < levels; i++) {
+            queues[i] = new LinkedList<>();
+        }
+        timeQuantum = timeQuantums;
+        currentTime = 0;
+    }
+
+    /**
+     * Adds a new process to the highest priority queue (queue 0).
+     *
+     * @param p The process to be added to the scheduler
+     */
+    public void addProcess(Process p) {
+        queues[0].add(p);
+    }
+
+    /**
+     * Executes the scheduling process by running the processes in all queues,
+     * promoting or demoting them based on their completion status and behavior.
+     * The process continues until all queues are empty.
+     */
+    public void run() {
+        while (!allQueuesEmpty()) {
+            for (int i = 0; i < queues.length; i++) {
+                Queue<Process> queue = queues[i];
+                if (!queue.isEmpty()) {
+                    Process p = queue.poll();
+                    int quantum = timeQuantum[i];
+
+                    // Execute the process for the minimum of the time quantum or the remaining time
+                    int timeSlice = Math.min(quantum, p.remainingTime);
+                    p.execute(timeSlice);
+                    currentTime += timeSlice; // Update the system's current time
+
+                    if (p.isFinished()) {
+                        System.out.println("Process " + p.pid + " finished at time " + currentTime);
+                    } else {
+                        if (i < queues.length - 1) {
+                            p.priority++; // Demote the process to the next lower priority queue
+                            queues[i + 1].add(p); // Add to the next queue level
+                        } else {
+                            queues[i].add(p); // Stay in the same queue if it's the last level
+                        }
+                    }
+                }
+            }
+        }
+    }
+
+    /**
+     * Helper function to check if all the queues are empty (i.e., no process is
+     * left to execute).
+     *
+     * @return true if all queues are empty, otherwise false
+     */
+    private boolean allQueuesEmpty() {
+        for (Queue<Process> queue : queues) {
+            if (!queue.isEmpty()) {
+                return false;
+            }
+        }
+        return true;
+    }
+
+    /**
+     * Retrieves the current time of the scheduler, which reflects the total time
+     * elapsed during the execution of all processes.
+     *
+     * @return The current time in the system
+     */
+    public int getCurrentTime() {
+        return currentTime;
+    }
+}
+
+/**
+ * Represents a process in the Multi-Level Feedback Queue (MLFQ) scheduling
+ * algorithm.
+ */
+class Process {
+    int pid;
+    int burstTime;
+    int remainingTime;
+    int arrivalTime;
+    int priority;
+
+    /**
+     * Constructor to initialize a new process.
+     *
+     * @param pid         Process ID
+     * @param burstTime   CPU Burst Time (time required for the process)
+     * @param arrivalTime Arrival time of the process
+     */
+    public Process(int pid, int burstTime, int arrivalTime) {
+        this.pid = pid;
+        this.burstTime = burstTime;
+        this.remainingTime = burstTime;
+        this.arrivalTime = arrivalTime;
+        this.priority = 0;
+    }
+
+    /**
+     * Executes the process for a given time slice.
+     *
+     * @param timeSlice The amount of time the process is executed
+     */
+    public void execute(int timeSlice) {
+        remainingTime -= timeSlice;
+        if (remainingTime < 0)
+            remainingTime = 0;
+    }
+
+    /**
+     * Checks if the process has finished execution.
+     *
+     * @return true if the process is finished, otherwise false
+     */
+    public boolean isFinished() {
+        return remainingTime == 0;
+    }
+}

src/test/java/com/thealgorithms/scheduling/MLFQSchedulerTest.java

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+package com.thealgorithms.scheduling;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.Test;
+
+public class MLFQSchedulerTest {
+
+    @Test
+    void testMLFQScheduling() {
+        // Create MLFQ Scheduler with 3 levels and time quantum for each level
+        int[] timeQuantums = {4, 8, 12}; // Example of different quantum for each queue
+        MLFQScheduler scheduler = new MLFQScheduler(3, timeQuantums);
+
+        // Add processes to the scheduler
+        scheduler.addProcess(new Process(1, 10, 0)); // pid=1, burstTime=10, arrivalTime=0
+        scheduler.addProcess(new Process(2, 15, 0)); // pid=2, burstTime=15, arrivalTime=0
+        scheduler.addProcess(new Process(3, 25, 0)); // pid=3, burstTime=25, arrivalTime=0
+
+        // Run the scheduler
+        scheduler.run();
+
+        // Check current time after all processes are finished
+        assertEquals(50, scheduler.getCurrentTime());
+    }
+
+    @Test
+    void testProcessCompletionOrder() {
+        int[] timeQuantums = { 3, 6, 9 };
+        MLFQScheduler scheduler = new MLFQScheduler(3, timeQuantums);
+
+        Process p1 = new Process(1, 10, 0);
+        Process p2 = new Process(2, 5, 0);
+        Process p3 = new Process(3, 20, 0);
+
+        scheduler.addProcess(p1);
+        scheduler.addProcess(p2);
+        scheduler.addProcess(p3);
+
+        scheduler.run();
+
+        // After running, current time should match the total burst time for all
+        // processes
+        assertEquals(35, scheduler.getCurrentTime());
+    }
+}