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Delete non_preemptive_sjf_scheduling.cpp
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DoGoodCoder
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/**
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* @file
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* @brief Implementation of SJF CPU scheduling algorithm
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* @details
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* shortest job first (SJF), also known as shortest job next (SJN), is a scheduling policy
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* that selects for execution the waiting process with the smallest execution time.
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* SJN is a non-preemptive algorithm. Shortest remaining time is a preemptive variant of SJN.
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* @link https://www.guru99.com/shortest-job-first-sjf-scheduling.html
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* @author [Lakshmi Srikumar](https://github.com/LakshmiSrikumar)
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*/
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#include <algorithm> /// for sorting
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#include <cassert> /// for assert
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#include <random> /// random number generation
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#include <iomanip> /// for formatting the output
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#include <iostream> /// for IO operations
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#include <queue> /// for std::priority_queue
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#include <unordered_set> /// for std::unordered_set
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#include <vector> /// for std::vector
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using std::cin;
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using std::cout;
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using std::endl;
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using std::get;
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using std::left;
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using std::make_tuple;
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using std::priority_queue;
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using std::tuple;
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using std::unordered_set;
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using std::vector;
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/**
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* @brief Comparator function for sorting a vector
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* @tparam S Data type of Process ID
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* @tparam T Data type of Arrival time
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* @tparam E Data type of Burst time
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* @param t1 tuple containing process id, arrival time and burst time
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* @param t2 tuple containing process id, arrival time and burst time
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* @returns true if t1 and t2 are in the CORRECT order
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* @returns false if t1 and t2 are in the INCORRECT order
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*/
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template <typename S, typename T, typename E>
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bool sortcol(tuple<S, T, E>& t1, tuple<S, T, E>& t2) {
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if (get<1>(t1) < get<1>(t2)) {
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return true;
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} else if (get<1>(t1) == get<1>(t2) && get<0>(t1) < get<0>(t2)) {
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return true;
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}
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return false;
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}
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/**
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* @class Compare
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* @brief Comparator class for priority queue
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* @tparam S Data type of Process ID
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* @tparam T Data type of Arrival time
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* @tparam E Data type of Burst time
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*/
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template <typename S, typename T, typename E>
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class Compare {
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public:
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/**
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* @param t1 First tuple
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* @param t2 Second tuple
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* @brief A comparator function that checks whether to swap the two tuples
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* or not.
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* @link Refer to
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* https://www.geeksforgeeks.org/comparator-class-in-c-with-examples/ for
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* detailed description of comparator
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* @returns true if the tuples SHOULD be swapped
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* @returns false if the tuples SHOULDN'T be swapped
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*/
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bool operator()(tuple<S, T, E, double, double, double>& t1,
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tuple<S, T, E, double, double, double>& t2) {
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// Compare burst times for SJF
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if (get<2>(t2) < get<2>(t1)) {
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return true;
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}
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// If burst times are the same, compare arrival times
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else if (get<2>(t2) == get<2>(t1)) {
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return get<1>(t2) < get<1>(t1);
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}
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return false;
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}
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};
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/**
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* @class SJF
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* @brief Class which implements the SJF scheduling algorithm
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* @tparam S Data type of Process ID
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* @tparam T Data type of Arrival time
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* @tparam E Data type of Burst time
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*/
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template <typename S, typename T, typename E>
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class SJF {
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/**
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* Priority queue of schedules(stored as tuples) of processes.
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* In each tuple
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* 1st element: Process ID
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* 2nd element: Arrival Time
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* 3rd element: Burst time
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* 4th element: Completion time
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* 5th element: Turnaround time
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* 6th element: Waiting time
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*/
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priority_queue<tuple<S, T, E, double, double, double>,
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vector<tuple<S, T, E, double, double, double>>,
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Compare<S, T, E>> schedule;
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// Stores final status of all the processes after completing the execution.
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vector<tuple<S, T, E, double, double, double>> result;
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// Stores process IDs. Used for confirming absence of a process while it.
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unordered_set<S> idList;
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public:
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/**
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* @brief Adds the process to the ready queue if it isn't already there
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* @param id Process ID
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* @param arrival Arrival time of the process
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* @param burst Burst time of the process
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* @returns void
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*
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*/
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void addProcess(S id, T arrival, E burst) {
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// Add if a process with process ID as id is not found in idList.
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if (idList.find(id) == idList.end()) {
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tuple<S, T, E, double, double, double> t =
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make_tuple(id, arrival, burst, 0, 0, 0);
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schedule.push(t);
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idList.insert(id);
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}
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}
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/**
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* @brief Algorithm for scheduling CPU processes according to the Shortest Job
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First (SJF) scheduling algorithm.
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*
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* @details Non pre-emptive SJF is an algorithm that schedules processes based on the length
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* of their burst times. The process with the smallest burst time is executed first.
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* In a non-preemptive scheduling algorithm, once a process starts executing,
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* it runs to completion without being interrupted.
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*
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* I used a min priority queue because it allows you to efficiently pick the process
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* with the smallest burst time in constant time, by maintaining a priority order where
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* the shortest burst process is always at the front.
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*
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* @returns void
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*/
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vector<tuple<S, T, E, double, double, double>> scheduleForSJF() {
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// Variable to keep track of time elapsed so far
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double timeElapsed = 0;
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while (!schedule.empty()) {
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tuple<S, T, E, double, double, double> cur = schedule.top();
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// If the current process arrived at time t2, the last process
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// completed its execution at time t1, and t2 > t1.
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if (get<1>(cur) > timeElapsed) {
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timeElapsed += get<1>(cur) - timeElapsed;
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}
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// Add Burst time to time elapsed
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timeElapsed += get<2>(cur);
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// Completion time of the current process will be same as time
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// elapsed so far
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get<3>(cur) = timeElapsed;
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// Turnaround time = Completion time - Arrival time
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get<4>(cur) = get<3>(cur) - get<1>(cur);
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// Waiting time = Turnaround time - Burst time
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get<5>(cur) = get<4>(cur) - get<2>(cur);
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result.push_back(cur);
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schedule.pop();
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}
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return result;
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}
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/**
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* @brief Utility function for printing the status of each process after
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* execution
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* @returns void
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*/
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void printResult() {
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cout << "Status of all processes post completion is as follows:" << endl;
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cout << std::setw(17) << left << "Process ID" << std::setw(17) << left
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<< "Arrival Time" << std::setw(17) << left << "Burst Time"
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<< std::setw(17) << left << "Completion Time" << std::setw(17)
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<< left << "Turnaround Time" << std::setw(17) << left
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<< "Waiting Time" << endl;
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for (size_t i{}; i < result.size(); i++) {
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cout << std::setprecision(2) << std::fixed << std::setw(17) << left
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<< get<0>(result[i]) << std::setw(17) << left
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<< get<1>(result[i]) << std::setw(17) << left
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<< get<2>(result[i]) << std::setw(17) << left
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<< get<3>(result[i]) << std::setw(17) << left
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<< get<4>(result[i]) << std::setw(17) << left
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<< get<5>(result[i]) << endl;
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}
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}
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};
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/**
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* @brief Computes the final status of processes after applying non-preemptive SJF scheduling
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* @tparam S Data type of Process ID
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* @tparam T Data type of Arrival time
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* @tparam E Data type of Burst time
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* @param input A vector of tuples containing Process ID, Arrival time, and Burst time
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* @returns A vector of tuples containing Process ID, Arrival time, Burst time,
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* Completion time, Turnaround time, and Waiting time
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*/
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template <typename S, typename T, typename E>
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vector<tuple<S, T, E, double, double, double>> get_final_status(
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vector<tuple<S, T, E>> input) {
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// Sort the processes based on Arrival time and then Burst time
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sort(input.begin(), input.end(), sortcol<S, T, E>);
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// Result vector to hold the final status of each process
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vector<tuple<S, T, E, double, double, double>> result(input.size());
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double timeElapsed = 0;
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for (size_t i = 0; i < input.size(); i++) {
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// Extract Arrival time and Burst time
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T arrival = get<1>(input[i]);
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E burst = get<2>(input[i]);
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// If the CPU is idle, move time to the arrival of the next process
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if (arrival > timeElapsed) {
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timeElapsed = arrival;
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}
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// Update timeElapsed by adding the burst time
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timeElapsed += burst;
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// Calculate Completion time, Turnaround time, and Waiting time
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double completion = timeElapsed;
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double turnaround = completion - arrival;
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double waiting = turnaround - burst;
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// Store the results in the result vector
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result[i] = make_tuple(get<0>(input[i]), arrival, burst, completion, turnaround, waiting);
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}
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return result;
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}
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/**
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* @brief Self-test implementations
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* @returns void
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*/
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static void test() {
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// A vector to store the results of all processes across all test cases.
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vector<tuple<uint32_t, uint32_t, uint32_t, double, double, double>> finalResult;
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for (int i{}; i < 100; i++) {
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std::random_device rd; // Seeding
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std::mt19937 eng(rd());
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std::uniform_int_distribution<> distr(1, 100);
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uint32_t n = distr(eng);
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SJF<uint32_t, uint32_t, uint32_t> readyQueue;
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vector<tuple<uint32_t, uint32_t, uint32_t>> input(n);
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// Generate random arrival and burst times
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for (uint32_t i{}; i < n; i++) {
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get<0>(input[i]) = i;
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get<1>(input[i]) = distr(eng); // Random arrival time
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get<2>(input[i]) = distr(eng); // Random burst time
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}
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// Add processes to the queue
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for (uint32_t i{}; i < n; i++) {
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readyQueue.addProcess(get<0>(input[i]), get<1>(input[i]), get<2>(input[i]));
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}
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// Schedule processes using SJF
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vector<tuple<uint32_t, uint32_t, uint32_t, double, double, double>> beforeResult = readyQueue.scheduleForSJF();
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// Append the results of this test case to the final result
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finalResult.insert(finalResult.end(), partialResult.begin(), partialResult.end());
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}
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// Now, print the results after all test cases
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cout << "Status of all processes post completion is as follows:" << endl;
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cout << std::setw(17) << left << "Process ID" << std::setw(17) << left
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<< "Arrival Time" << std::setw(17) << left << "Burst Time"
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<< std::setw(17) << left << "Completion Time" << std::setw(17)
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<< left << "Turnaround Time" << std::setw(17) << left << "Waiting Time" << endl;
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// Loop through the final result and print all process details
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for (size_t i{}; i < finalResult.size(); i++) {
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cout << std::setprecision(2) << std::fixed << std::setw(17) << left
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<< get<0>(finalResult[i]) << std::setw(17) << left
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<< get<1>(finalResult[i]) << std::setw(17) << left
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<< get<2>(finalResult[i]) << std::setw(17) << left
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<< get<3>(finalResult[i]) << std::setw(17) << left
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<< get<4>(finalResult[i]) << std::setw(17) << left
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<< get<5>(finalResult[i]) << endl;
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}
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cout << "All the tests have successfully passed!" << endl;
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}
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/**
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* @brief Entry point of the program
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*/
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int main() {
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test();
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return 0;
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}
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