OS-Labs/lab3/scheduler.cpp

#include <iostream>
#include <fstream>
#include <cstring>
#include <unistd.h>
#include <chrono>
#include <sstream>
#include <string>
#include <bits/stdc++.h>

using namespace std;

struct process_detail {
	//cpu_burst_times[0] is arrival time
	int pid;
	vector<int> burst_times;
	int in_cpu;
	int current_burst_index;
};

struct clock{
	int push_signal; //boolean
	int timer;

};

vector<process_detail> processes;
queue<process_detail*> ready_queue_fifo;
struct process_detail* CPU = NULL;
vector<process_detail*> waiting;

ofstream output_file("cpu_times.txt");

//  -------------------------------------- THE FIFO --------------------------------------------------

void fifo() {

	//clock initialized to 0
	struct clock time;
	memset(&time, 0, sizeof(struct clock));
	time.timer = 0;
	time.push_signal = 0;
	int process_count = processes.size();
	int completed_processes = 0;

	while(completed_processes < process_count){

		// ready queue, waiting queue, cpu in check, ready queue subtraction, waiting queue subtraction

		// breaking from the infinite loop
		for(int i = 0; i < process_count; ++i) {
			if(processes[i].burst_times[processes[i].current_burst_index] == -2) {
				completed_processes++;
			}
		}

		//managing arrival times
		for(int i = 0; i < process_count; ++i) {
			//if process not in cpu
			if(processes[i].in_cpu != 1) {
				if(time.timer == processes[i].burst_times[0]) {
					ready_queue_fifo.push(&processes[i]);
					processes[i].current_burst_index++;
				}
			}
		}
		
		// managing waiting queue
		for(int j = 0; j < waiting.size(); ++j) {
			if(waiting[j] != NULL) {
				if(waiting[j]->burst_times[waiting[j]->current_burst_index] == 0) {
					ready_queue_fifo.push(waiting[j]);
					waiting[j]->current_burst_index++;
					waiting[j] = NULL;
				}
			}
		}

		if(CPU == NULL && !ready_queue_fifo.empty()) {
			CPU = ready_queue_fifo.front();
			CPU->in_cpu = 1;
			// Record in_time when the process enters the CPU
			output_file << "P" << CPU->pid+1 << ",1" << " " << time.timer;
			ready_queue_fifo.pop();

		}

		else if(CPU != NULL){
			//check cpu_burst complete
			for(int i = 0; i < process_count; ++i) {
				if(processes[i].in_cpu == 1) {
					if(CPU->burst_times[processes[i].current_burst_index] == 0){
						// Record out_time when the process exits the CPU
                        output_file << " " << time.timer << endl;
						CPU->in_cpu = 0;
						CPU->current_burst_index++;
						waiting.push_back(CPU); // process added to waiting queue
						if(!ready_queue_fifo.empty()) {
							CPU = ready_queue_fifo.front(); // process added to CPU
							CPU->in_cpu = 1;
							output_file << "P" << CPU->pid+1 << ",1" << " " << time.timer; // New entry time
							ready_queue_fifo.pop();
						}
						else {
							CPU = NULL;
						}
					}
				}
			}
		}


		if(CPU != NULL) {
			CPU->burst_times[CPU->current_burst_index]--;
		}

		for(int j = 0; j < waiting.size(); ++j) {
			if(waiting[j] != NULL) {
				if(waiting[j]->burst_times[waiting[j]->current_burst_index] != 0) {
					waiting[j]->burst_times[waiting[j]->current_burst_index]--; // reducing the io burst till it reaches 0
				}
			}
		}

		time.timer++;
	}
	output_file.close();
	return;
}



// ----------------------------------------- The Shortest Job Fist -------------------------------------------
// Custom comparator for the priority queue
struct Compare {
    bool operator()(process_detail* a, process_detail* b) {
        // Compare the elements in the vector at the given indices
        return a->burst_times[a->current_burst_index] > b->burst_times[b->current_burst_index];
    }
};

priority_queue<process_detail*, vector<process_detail*>, Compare> ready_queue;

void sjf() {

	//clock initialized to 0
	struct clock time;
	memset(&time, 0, sizeof(struct clock));
	time.timer = 0;
	time.push_signal = 0;
	int process_count = processes.size();
	int completed_processes = 0;

	while(completed_processes < process_count){

		// ready queue, waiting queue, cpu in check, ready queue subtraction, waiting queue subtraction

		// breaking from the infinite loop
		for(int i = 0; i < process_count; ++i) {
			if(processes[i].burst_times[processes[i].current_burst_index] == -2) {
				completed_processes++;
			}
		}

		//managing arrival times
		for(int i = 0; i < process_count; ++i) {
			//if process not in cpu
			if(processes[i].in_cpu != 1) {
				if(time.timer == processes[i].burst_times[0]) {
					ready_queue.push(&processes[i]);
					processes[i].current_burst_index++;
				}
			}
		}
		
		// managing waiting queue
		for(int j = 0; j < waiting.size(); ++j) {
			if(waiting[j] != NULL) {
				if(waiting[j]->burst_times[waiting[j]->current_burst_index] == 0) {
					ready_queue.push(waiting[j]);
					waiting[j]->current_burst_index++;
					waiting[j] = NULL;
				}
			}
		}

		if(CPU == NULL && !ready_queue.empty()) {
			CPU = ready_queue.top();
			CPU->in_cpu = 1;
			// Record in_time when the process enters the CPU
			output_file << "P" << CPU->pid+1 << ",1" << " " << time.timer;
			ready_queue.pop();
		}

		else if(CPU != NULL){
			//check cpu_burst complete
			for(int i = 0; i < process_count; ++i) {
				if(processes[i].in_cpu == 1) {
					if(CPU->burst_times[processes[i].current_burst_index] == 0){
						// Record out_time when the process exits the CPU
                        output_file << " " << time.timer << endl;
						CPU->in_cpu = 0;
						CPU->current_burst_index++;
						waiting.push_back(CPU); // process added to waiting queue
						if(!ready_queue.empty()) {
							CPU = ready_queue.top(); // process added to CPU
							CPU->in_cpu = 1;
							output_file << "P" << CPU->pid+1 << ",1" << " " << time.timer; // New entry time
							ready_queue.pop();
						}
						else {
							CPU = NULL;
						}
					}
				}
			}
		}


		if(CPU != NULL) {
			// reducing the cpu burst till it reaches 0
			CPU->burst_times[CPU->current_burst_index]--;
		}

		for(int j = 0; j < waiting.size(); ++j) {
			if(waiting[j] != NULL) {
				if(waiting[j]->burst_times[waiting[j]->current_burst_index] != 0) {
					// reducing the io burst till it reaches 0
					waiting[j]->burst_times[waiting[j]->current_burst_index]--; 
				}
			}
		}

		time.timer++;
	}
	output_file.close();
	return;
}

// ------------------------------------Pre-emptive shortest job --------------------------------------------

void pre_sjf() {

	//clock initialized to 0
	struct clock time;
	memset(&time, 0, sizeof(struct clock));
	time.timer = 0;
	time.push_signal = 0;
	int process_count = processes.size();
	int completed_processes = 0;

	while(completed_processes < process_count){

		// ready queue, waiting queue, cpu in check, ready queue subtraction, waiting queue subtraction

		// breaking from the infinite loop
		for(int i = 0; i < process_count; ++i) {
			if(processes[i].burst_times[processes[i].current_burst_index] == -2) {
				completed_processes++;
			}
		}

		//managing arrival times
		for(int i = 0; i < process_count; ++i) {
			//if process not in cpu
			if(processes[i].in_cpu != 1) {
				if(time.timer == processes[i].burst_times[0]) {
					ready_queue.push(&processes[i]);
					if(CPU != NULL) {
						ready_queue.push(CPU);
						CPU->in_cpu = 0;
						output_file << " " << time.timer << endl;
						CPU = ready_queue.top();
						CPU->in_cpu = 1;
						output_file << "P" << CPU->pid+1 << ",1" << " " << time.timer; // New entry time
						ready_queue.pop();

					}
					processes[i].current_burst_index++;
				}
			}
		}
		
		// managing waiting queue
		for(int j = 0; j < waiting.size(); ++j) {
			if(waiting[j] != NULL) {
				if(waiting[j]->burst_times[waiting[j]->current_burst_index] == 0) {
					ready_queue.push(waiting[j]);
					if(CPU != NULL) {
						ready_queue.push(CPU);
						CPU->in_cpu = 0;
						output_file << " " << time.timer << endl;
						CPU = ready_queue.top();
						CPU->in_cpu = 1;
						output_file << "P" << CPU->pid+1 << ",1" << " " << time.timer; // New entry time
						ready_queue.pop();

					}
					waiting[j]->current_burst_index++;
					waiting[j] = NULL;
				}
			}
		}

		if(CPU == NULL && !ready_queue.empty()) {
			CPU = ready_queue.top();
			CPU->in_cpu = 1;
			// Record in_time when the process enters the CPU
			output_file << "P" << CPU->pid+1 << ",1" << " " << time.timer;
			ready_queue.pop();
		}

		else if(CPU != NULL){
			//check cpu_burst complete
			for(int i = 0; i < process_count; ++i) {
				if(processes[i].in_cpu == 1) {
					if(CPU->burst_times[processes[i].current_burst_index] == 0){
						// Record out_time when the process exits the CPU
                        output_file << " " << time.timer << endl;
						CPU->in_cpu = 0;
						CPU->current_burst_index++;
						waiting.push_back(CPU); // process added to waiting queue
						if(!ready_queue.empty()) {
							CPU = ready_queue.top(); // process added to CPU
							CPU->in_cpu = 1;
							output_file << "P" << CPU->pid+1 << ",1" << " " << time.timer; // New entry time
							ready_queue.pop();
						}
						else {
							CPU = NULL;
						}
					}
				}
			}
		}


		if(CPU != NULL) {
			// reducing the cpu burst till it reaches 0
			CPU->burst_times[CPU->current_burst_index]--;
		}

		for(int j = 0; j < waiting.size(); ++j) {
			if(waiting[j] != NULL) {
				if(waiting[j]->burst_times[waiting[j]->current_burst_index] != 0) {
					// reducing the io burst till it reaches 0
					waiting[j]->burst_times[waiting[j]->current_burst_index]--; 
				}
			}
		}

		time.timer++;
	}
	output_file.close();
	return;
}


// ------------------------------------------- Round Robin --------------------------------------------------

void round_robin() {

	// Clock initialized to 0
	struct clock time;
	memset(&time, 0, sizeof(struct clock));
	time.timer = 0;
	time.push_signal = 5;
	int process_count = processes.size();
	int completed_processes = 0;
	int time_quantum = 2; // Define a time quantum for Round Robin

	// To keep track of the remaining quantum for the current process
	int current_quantum = 0;

	while (completed_processes < process_count) {
		// Ready queue, waiting queue, CPU in check, ready queue subtraction, waiting queue subtraction

		// Breaking from the loop
		for (int i = 0; i < process_count; ++i) {
			if (processes[i].burst_times[processes[i].current_burst_index] == -2) {
				completed_processes++;
			}
		}

		// Managing arrival times
		for (int i = 0; i < process_count; ++i) {
			// If process not in CPU
			if (processes[i].in_cpu != 1) {
				if (time.timer == processes[i].burst_times[0]) {
					ready_queue_fifo.push(&processes[i]);
					processes[i].current_burst_index++;
				}
			}
		}

		// Managing waiting queue
		for (int j = 0; j < waiting.size(); ++j) {
			if (waiting[j] != NULL) {
				if (waiting[j]->burst_times[waiting[j]->current_burst_index] == 0) {
					ready_queue_fifo.push(waiting[j]);
					waiting[j]->current_burst_index++;
					waiting[j] = NULL;
				}
			}
		}

		if (CPU == NULL && !ready_queue_fifo.empty()) {
			// Assign the first process from the ready queue to the CPU
			CPU = ready_queue_fifo.front();
			CPU->in_cpu = 1;
			// Record in_time when the process enters the CPU
			output_file << "P" << CPU->pid + 1 << ",1 " << time.timer;
			ready_queue_fifo.pop();
			current_quantum = time_quantum; // Reset the time quantum for the new process
		} 
		else if (CPU != NULL) {
			// Check if CPU burst is complete or quantum expired
			if (CPU->burst_times[CPU->current_burst_index] == 0 || current_quantum == 0) {
				// Record out_time when the process exits the CPU
				output_file << " " << time.timer << endl;
				CPU->in_cpu = 0;
				CPU->current_burst_index++;

				// If the process still has bursts left, move it to the waiting queue
				if (CPU->burst_times[CPU->current_burst_index] > 0) {
					waiting.push_back(CPU);
				}

				// Assign the next process from the ready queue to the CPU
				if (!ready_queue_fifo.empty()) {
					CPU = ready_queue_fifo.front();
					CPU->in_cpu = 1;
					output_file << "P" << CPU->pid + 1 << ",1 " << time.timer; // New entry time
					ready_queue_fifo.pop();
					current_quantum = time_quantum; // Reset the time quantum for the new process
				} 
				else {
					CPU = NULL;
				}
			}
		}

		if (CPU != NULL) {
			// Decrement the burst time of the process currently in the CPU
			CPU->burst_times[CPU->current_burst_index]--;
			current_quantum--; // Decrement the quantum counter
			// If quantum is exhausted but burst isn't finished, preempt the process
			if (current_quantum == 0 && CPU->burst_times[CPU->current_burst_index] > 0) {
				ready_queue_fifo.push(CPU); // Re-add the process to the ready queue
				CPU->in_cpu = 0;
				CPU = NULL; // Preempt the process from the CPU
			}
		}

		// Reduce the IO burst times of the processes in the waiting queue
		for (int j = 0; j < waiting.size(); ++j) {
			if (waiting[j] != NULL) {
				if (waiting[j]->burst_times[waiting[j]->current_burst_index] != 0) {
					waiting[j]->burst_times[waiting[j]->current_burst_index]--; // Reducing the IO burst until it reaches 0
				}
			}
		}

		time.timer++;
	}

	output_file.close();
	return;

}

int main(int argc, char **argv) {

    if(argc != 3)
	{
		cout <<"usage: ./scheduler.out <path-to-workload-file> <scheduler_algorithm>\nprovided arguments:\n";
		for(int i = 0; i < argc; i++)
			cout << argv[i] << "\n";
		return -1;
	}

    char *file_to_search_in = argv[1];
	char *scheduler_algorithm = argv[2];

    ifstream file(file_to_search_in, ios::binary);
    string buffer;
    int pid = 0;

    while(getline(file, buffer)) {
		if(buffer[0] == '<'){
			continue;
		}
		istringstream iss(buffer);
		string word;
		struct process_detail pd;
		memset(&pd,0,sizeof(struct process_detail));
		pd.pid = pid++;
		pd.current_burst_index = 0;

		while(iss>>word){
			pd.burst_times.push_back(stoi(word));
		}
		processes.push_back(pd);
    }

	map<string, int> temp;
	temp["fifo"] = 1;
	temp["sjf"] = 2;
	temp["pre_sjf"] = 3;
	temp["rr"] = 4;

	string temp1 = scheduler_algorithm;

	switch(temp[temp1]){
		case 1:
			fifo();
			break;
		case 2:
			sjf();
			break;
		case 3:
			pre_sjf();
			break;
		case 4:
			round_robin();
			break;
		default:
			cout << "enter fifo or sjf or pre_sjf or rr" << endl;
	}

    return 0;
}