Add SRTF Algorithm (#5011)

This commit is contained in:
mpousmali
2024-01-08 23:48:11 +02:00
committed by GitHub
parent 570f7e7ef6
commit fd84b0b10e
3 changed files with 131 additions and 0 deletions

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vscode: vscode:
extensions: extensions:
- xaver.clang-format - xaver.clang-format

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package com.thealgorithms.scheduling;
import com.thealgorithms.devutils.entities.ProcessDetails;
import java.util.ArrayList;
import java.util.List;
/**
* Implementation of Shortest Remaining Time First Scheduling Algorithm.
* In the SRTF scheduling algorithm, the process with the smallest amount of time remaining until completion is selected to execute.
* Example:
* Consider the processes p1, p2 and the following table with info about their arrival and burst time:
* Process | Burst Time | Arrival Time
* P1 | 6 ms | 0 ms
* P2 | 2 ms | 1 ms
* In this example, P1 will be executed at time = 0 until time = 1 when P2 arrives. At time = 2, P2 will be executed until time = 4. At time 4, P2 is done, and P1 is executed again to be done.
* That's a simple example of how the algorithm works.
* More information you can find here -> https://en.wikipedia.org/wiki/Shortest_remaining_time
*/
public class SRTFScheduling {
protected List<ProcessDetails> processes;
protected List<String> ready;
/**
* Constructor
* @param processes ArrayList of ProcessDetails given as input
*/
public SRTFScheduling(ArrayList<ProcessDetails> processes) {
this.processes = new ArrayList<>();
ready = new ArrayList<>();
this.processes = processes;
}
public void evaluateScheduling() {
int time = 0, cr = 0; // cr=current running process, time= units of time
int n = processes.size();
int[] remainingTime = new int[n];
/* calculating remaining time of every process and total units of time */
for (int i = 0; i < n; i++) {
remainingTime[i] = processes.get(i).getBurstTime();
time += processes.get(i).getBurstTime();
}
/* if the first process doesn't arrive at 0, we have more units of time */
if (processes.get(0).getArrivalTime() != 0) {
time += processes.get(0).getArrivalTime();
}
/* printing id of the process which is executed at every unit of time */
// if the first process doesn't arrive at 0, we print only \n until it arrives
if (processes.get(0).getArrivalTime() != 0) {
for (int i = 0; i < processes.get(0).getArrivalTime(); i++) {
ready.add(null);
}
}
for (int i = processes.get(0).getArrivalTime(); i < time; i++) {
/* checking if there's a process with remaining time less than current running process.
If we find it, then it executes. */
for (int j = 0; j < n; j++) {
if (processes.get(j).getArrivalTime() <= i && (remainingTime[j] < remainingTime[cr] && remainingTime[j] > 0 || remainingTime[cr] == 0)) {
cr = j;
}
}
ready.add(processes.get(cr).getProcessId());
remainingTime[cr]--;
}
}
}

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package com.thealgorithms.scheduling;
import static org.junit.jupiter.api.Assertions.assertEquals;
import com.thealgorithms.devutils.entities.ProcessDetails;
import java.util.ArrayList;
import org.junit.jupiter.api.Test;
class SRTFSchedulingTest {
ArrayList<ProcessDetails> processes;
public void initialization() {
processes = new ArrayList<>();
processes.add(new ProcessDetails("4", 0, 3));
processes.add(new ProcessDetails("3", 1, 8));
processes.add(new ProcessDetails("1", 2, 6));
processes.add(new ProcessDetails("5", 4, 4));
processes.add(new ProcessDetails("2", 5, 2));
}
@Test
public void Constructor() {
initialization();
SRTFScheduling s = new SRTFScheduling(processes);
assertEquals(3, s.processes.get(0).getBurstTime());
assertEquals(8, s.processes.get(1).getBurstTime());
assertEquals(6, s.processes.get(2).getBurstTime());
assertEquals(4, s.processes.get(3).getBurstTime());
assertEquals(2, s.processes.get(4).getBurstTime());
}
@Test
void evaluateScheduling() {
initialization();
SRTFScheduling s = new SRTFScheduling(processes);
s.evaluateScheduling();
assertEquals("4", s.ready.get(0));
assertEquals("4", s.ready.get(1));
assertEquals("4", s.ready.get(2));
assertEquals("1", s.ready.get(3));
assertEquals("5", s.ready.get(4));
assertEquals("2", s.ready.get(5));
assertEquals("2", s.ready.get(6));
assertEquals("5", s.ready.get(7));
assertEquals("5", s.ready.get(8));
assertEquals("5", s.ready.get(9));
assertEquals("1", s.ready.get(10));
assertEquals("1", s.ready.get(11));
assertEquals("1", s.ready.get(12));
assertEquals("1", s.ready.get(13));
assertEquals("1", s.ready.get(14));
assertEquals("3", s.ready.get(15));
assertEquals("3", s.ready.get(16));
assertEquals("3", s.ready.get(17));
assertEquals("3", s.ready.get(18));
assertEquals("3", s.ready.get(19));
assertEquals("3", s.ready.get(20));
assertEquals("3", s.ready.get(21));
assertEquals("3", s.ready.get(22));
}
}