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Add MLFQ Scheduler (#5575)

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This commit is contained in:
Hardik Pawar
2024-10-06 12:42:11 +05:30
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parent 4008e4967c
commit 1feceb7d11
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6
DIRECTORY.md
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@ -42,6 +42,7 @@
* [AES](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/AES.java)
* [AESEncryption](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/AESEncryption.java)
* [AffineCipher](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/AffineCipher.java)
* [Autokey](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/Autokey.java)
* [Blowfish](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/Blowfish.java)
* [Caesar](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/Caesar.java)
* [ColumnarTranspositionCipher](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/ColumnarTranspositionCipher.java)
@ -203,6 +204,7 @@
* [SameTreesCheck](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/trees/SameTreesCheck.java)
* [SegmentTree](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/trees/SegmentTree.java)
* [SplayTree](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/trees/SplayTree.java)
* [Treap](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/trees/Treap.java)
* [TreeRandomNode](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/trees/TreeRandomNode.java)
* [TrieImp](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/trees/TrieImp.java)
* [VerticalOrderTraversal](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/trees/VerticalOrderTraversal.java)
@ -457,6 +459,7 @@
* [GenerateSubsets](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/Recursion/GenerateSubsets.java)
* scheduling
* [FCFSScheduling](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/scheduling/FCFSScheduling.java)
* [MLFQScheduler](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/scheduling/MLFQScheduler.java)
* [PreemptivePriorityScheduling](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/scheduling/PreemptivePriorityScheduling.java)
* [RRScheduling](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/scheduling/RRScheduling.java)
* [SJFScheduling](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/scheduling/SJFScheduling.java)
@ -618,6 +621,7 @@
* ciphers
* a5
* [LFSRTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/a5/LFSRTest.java)
* [AutokeyTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/AutokeyTest.java)
* [BlowfishTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/BlowfishTest.java)
* [CaesarTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/CaesarTest.java)
* [DESTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/DESTest.java)
@ -728,6 +732,7 @@
* [PreOrderTraversalTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/trees/PreOrderTraversalTest.java)
* [SameTreesCheckTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/trees/SameTreesCheckTest.java)
* [SplayTreeTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/trees/SplayTreeTest.java)
* [TreapTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/trees/TreapTest.java)
* [TreeTestUtils](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/trees/TreeTestUtils.java)
* [TrieImpTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/trees/TrieImpTest.java)
* [VerticalOrderTraversalTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/trees/VerticalOrderTraversalTest.java)
@ -911,6 +916,7 @@
* [GenerateSubsetsTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/Recursion/GenerateSubsetsTest.java)
* scheduling
* [FCFSSchedulingTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/scheduling/FCFSSchedulingTest.java)
* [MLFQSchedulerTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/scheduling/MLFQSchedulerTest.java)
* [PreemptivePrioritySchedulingTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/scheduling/PreemptivePrioritySchedulingTest.java)
* [RRSchedulingTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/scheduling/RRSchedulingTest.java)
* [SJFSchedulingTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/scheduling/SJFSchedulingTest.java)

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src/main/java/com/thealgorithms/scheduling/MLFQScheduler.java Normal file
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package com.thealgorithms.scheduling;
import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;
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 List<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 ArrayList<>(levels);
for (int i = 0; i < levels; i++) {
queues.add(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.get(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.size(); i++) {
Queue<Process> queue = queues.get(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.size() - 1) {
p.priority++; // Demote the process to the next lower priority queue
queues.get(i + 1).add(p); // Add to the next queue level
} else {
queue.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
*/
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;
}
}

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src/test/java/com/thealgorithms/scheduling/MLFQSchedulerTest.java Normal file
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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());
}
}