FCFS.c

#include "FCFS.h"

void FCFS(Process *processes[], const unsigned int p_len,
		  unsigned int *finishedTime, unsigned int *responseTime, int *ganttChart)
{
	bool status_period_0[p_len];
	bool status_period_1[p_len];
	bool allFinished = false;
	for (int i = 0; i < p_len; i++) {
		status_period_0[i] = false;
		status_period_1[i] = false;
	}

	unsigned int timeElapsed = minArrivalTime(processes, p_len);

	while (!allFinished) {

		// Retain the earliest process in the ready queue.
		unsigned int currentProcess = findFirstProcessInQueue(processes, p_len, status_period_0, status_period_1);

		// Checking if we have some idle CPU time by comparing the time in which the last process gave up the CPU,
		// And the new process has arrived.
		if (getArrivalTime(processes[currentProcess]) > timeElapsed) {
			for (unsigned int t = timeElapsed; t < getArrivalTime(processes[currentProcess]); t++) {
				// '-1' identifies idle state.
				ganttChart[t] = -1;
			}
			timeElapsed = getArrivalTime(processes[currentProcess]);
		}

		// The variable "period" identifies which burst time must happen.
		bool period;
		if (!status_period_0[currentProcess]) {
			period = 0;
			responseTime[currentProcess] = timeElapsed - getArrivalTime(processes[currentProcess]);
		}
		else if (status_period_0[currentProcess] && !status_period_1[currentProcess]) {
			period = 1;
		}

		// It does NOT happen, but if we have unexpected values, it will exit.
		else { exit(1); }

		for (unsigned int t = timeElapsed; t < timeElapsed + getBurstTime(processes[currentProcess], period); t++) {
			ganttChart[t] = (int) currentProcess;
		}

		timeElapsed += getBurstTime(processes[currentProcess], period);

		// After the first period is done, we update the arrival time of the process with the time the process would
		// come back from the IO.
		if (period == 0) {
			status_period_0[currentProcess] = true;
			setArrivalTime(processes[currentProcess], timeElapsed + getIOTime(processes[currentProcess]));
		}

		// After the second period is done, the process is finished, and we can store the time
		// in which the process ended.
		else {
			status_period_1[currentProcess] = true;
			finishedTime[currentProcess] = timeElapsed;
		}

		// Checking if all processes have been completed.
		bool flag = false;
		for (int i = 0; i < p_len; i++) {
			if (!status_period_0[i] || !status_period_1[i]) {
				flag = true;
				break;
			};
		}
		allFinished = !flag;
	}
}