TheAlgorithms-C-Plus-Plus/cpu_scheduling_algorithms/fcfs_scheduling.cpp

/**
 * @file fcfs_scheduling.cpp
 * @brief Implementation of FCFS CPU scheduling algorithm
 * @details
 * FCFS is a non-preemptive CPU scheduling algorithm in which whichever process
 * arrives first, gets executed first. If two or more processes arrive
 * simultaneously, the process with smaller process ID gets executed first.
 * @link https://bit.ly/3ABNXOC
 * @author Pratyush Vatsa(https://github.com/Pratyush219)
 */

#include <iomanip>        // for formatting the output
#include <iostream>       // for IO operations
#include <queue>          // for priority_queue
#include <unordered_set>  // for using unordered_set
#include <vector>         // for using vector

using std::cin;
using std::cout;
using std::endl;
using std::get;
using std::left;
using std::make_tuple;
using std::priority_queue;
using std::tuple;
using std::unordered_set;
using std::vector;

/**
 * @class Compare
 * @brief Comparator class for priority queue
 * @tparam S: Data type of Process ID
 * @tparam T: Data type of Arrival time
 * @tparam E: Data type of Burst time
 */
template <typename S, typename T, typename E>
class Compare {
 public:
    /**
     * @param t1: first tuple
     * @param t2: second tuple
     * @brief A comparator function that checks whether to swap the two tuples
     * or not.
     * @link Refer
     * https://www.geeksforgeeks.org/comparator-class-in-c-with-examples/ for
     * detailed description of comparator
     * @returns true if the tuples should be swapped, false othewise
     */
    bool operator()(tuple<S, T, E, double, double, double>& t1,
                    tuple<S, T, E, double, double, double>& t2) {
        // Compare arrival times
        if (get<1>(t2) < get<1>(t1)) {
            return true;
        }
        // If arrival times are same, then compare Process IDs
        else if (get<1>(t2) == get<1>(t1)) {
            return get<0>(t2) < get<0>(t1);
        }
        return false;
    }
};

/**
 * @class FCFS
 * @brief Class which implements the FCFS scheduling algorithm
 * @tparam S: Data type of Process ID
 * @tparam T: Data type of Arrival time
 * @tparam E: Data type of Burst time
 */
template <typename S, typename T, typename E>
class FCFS {
    /**
     * Priority queue of schedules(stored as tuples) of processes.
     * In each tuple
     * 1st element: Process ID
     * 2nd element: Arrival Time
     * 3rd element: Burst time
     * 4th element: Completion time
     * 5th element: Turnaround time
     * 6th element: Waiting time
     */
    priority_queue<tuple<S, T, E, double, double, double>,
                   vector<tuple<S, T, E, double, double, double>>,
                   Compare<S, T, E>>
        schedule;

    // Stores final status of all the processes after completing the execution.
    vector<tuple<S, T, E, double, double, double>> result;

    // Stores process IDs. Used for confirming absence of a process while adding
    // it.
    unordered_set<S> idList;

 public:
    /**
     * @brief adds the process to the ready queue if it isn't already there
     * @param ID: Process ID
     * @param arrival: Arrival time of the process
     * @param burst: Burst time of the process
     * @returns void
     *
     */
    void addProcess(S id, T arrival, E burst) {
        // Add if a process with process ID as id is not found in idList.
        if (idList.find(id) == idList.end()) {
            tuple<S, T, E, double, double, double> t =
                make_tuple(id, arrival, burst, 0, 0, 0);
            schedule.push(t);
            idList.insert(id);
        }
    }

    /**
     * @brief Algorithm for scheduling CPU processes according to the First Come
     * First Serve(FCFS) scheduling algorithm.
     *
     * @description FCFS is a non-preemptive algorithm in which the process
     * which arrives first gets executed first. If two or more processes arrive
     * together then the process with smaller process ID runs first (each
     * process has a unique proces ID).
     *
     * I used a min priority queue of tuples to accomplish this task. The
     * processes are ordered by their arrival times. If arrival times of some
     * processes are equal, then they are ordered by their process ID.
     *
     * @returns void
     */
    void scheduleForFcfs() {
        // Variable to keep track of time elapsed so far
        double timeElapsed = 0;

        while (!schedule.empty()) {
            tuple<S, T, E, double, double, double> cur = schedule.top();

            // If the next process arrived at time t2, the last process
            // completed its execution at time t1, and t2 > t1.
            if (get<1>(cur) > timeElapsed) {
                timeElapsed += get<1>(cur) - timeElapsed;
            }

            // Add Burst time to time elapsed
            timeElapsed += get<2>(cur);

            // Completion time of the current process will be same as time
            // elapsed so far
            get<3>(cur) = timeElapsed;

            // Turnaround time = Completion time - Arrival time
            get<4>(cur) = get<3>(cur) - get<1>(cur);

            // Waiting time = Turnaround time - Burst time
            get<5>(cur) = get<4>(cur) - get<2>(cur);

            result.push_back(cur);
            schedule.pop();
        }
        printResult();
    }

    /**
     * @brief Utility function for printing the status of each process after
     * execution
     * @returns void
     */
    void printResult() {
        cout << "Status of all the proceses post completion is as follows:"
             << endl;

        cout << std::setw(17) << left << "Process ID" << std::setw(17) << left
             << "Arrival Time" << std::setw(17) << left << "Burst Time"
             << std::setw(17) << left << "Completion Time" << std::setw(17)
             << left << "Turnaround Time" << std::setw(17) << left
             << "Waiting Time" << endl;

        for (size_t i{}; i < result.size(); i++) {
            cout << std::setprecision(2) << std::fixed << std::setw(17) << left
                 << get<0>(result[i]) << std::setw(17) << left
                 << get<1>(result[i]) << std::setw(17) << left
                 << get<2>(result[i]) << std::setw(17) << left
                 << get<3>(result[i]) << std::setw(17) << left
                 << get<4>(result[i]) << std::setw(17) << left
                 << get<5>(result[i]) << endl;
        }
    }
};

/**
 * @brief Entry point of the program
 * @returns 0 on exit
 */
int main() {
    FCFS<uint32_t, uint32_t, uint32_t> readyQueue;

    // Sample test case
    int n = 3;
    vector<tuple<uint32_t, uint32_t, uint32_t>> input = {
        make_tuple(1, 0, 30), make_tuple(2, 0, 5), make_tuple(3, 0, 5)};

    for (uint32_t i{}; i < n; i++) {
        readyQueue.addProcess(get<0>(input[i]), get<1>(input[i]),
                              get<2>(input[i]));
    }

    readyQueue.scheduleForFcfs();
    return 0;
}