ferry.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <pthread.h>
#include <semaphore.h>
#include <string.h>
#include <stdbool.h>
#include "ferry.h"

unsigned int numOfCars = 0;
unsigned int numOfCarsWaiting = 0;
unsigned int numOfCarsOnBoard = 0;
pthread_mutex_t mutex;
sem_t sem;
bool isFerryPresent = false;
bool isFerryTravelling = false;

void *embark(void *i)
{ // producer
    int id = *((int *)i);
    sleep(rand() % 5 + 1); // random arival time in range [1,5]
    pthread_mutex_lock(&mutex);
    numOfCarsWaiting++;
    pthread_mutex_unlock(&mutex);
    printf("Car #%d arrived at the port (cars waiting to board = %d)\n", id, numOfCarsWaiting);
    // wait for the ferry to arrive
    while (!isFerryPresent)
        sleep(1);

    //tofix while the ferry hasn't left and is full, some cars reach this point
    // we want them to wait until all cars have disembarked

    // start embarking if there is space on the ferry
    sem_wait(&sem);
    printf("Car #%d embarking on the ferry!\n", id);
    pthread_mutex_lock(&mutex); // enter critical region
    numOfCarsOnBoard++;
    numOfCarsWaiting--;
    pthread_mutex_unlock(&mutex); // leave critical region

    sleep(1); // embarking time
    printf("Car #%d embarked on the ferry!\n", id);

    // while ferry is waiting or travelling sleep/stay embarked
    while (isFerryPresent || isFerryTravelling)
        sleep(1);

    // disembark from the ferry
    pthread_mutex_lock(&mutex);
    numOfCarsOnBoard--;
    pthread_mutex_unlock(&mutex);
    printf("Car #%d disemabarked from the ferry!\n", id);
    sem_post(&sem);
    free(i);
    pthread_exit(NULL);
}

void *initFerrySchedule()
{ // consumer
    while (numOfCars > 0)
    {
        while (numOfCarsWaiting == 0 || numOfCarsOnBoard != 0)
            sleep(1);
        printf("Someone woke up the ferry!\nFerry is waiting for cars to board...\n");
        // signal that boarding is allowed
        pthread_mutex_lock(&mutex);
        isFerryPresent = true;
        isFerryTravelling = false;
        pthread_mutex_unlock(&mutex);
        sleep(7); // wait for cars to board
        printf("Ferry is leaving with %d cars on board\n", numOfCarsOnBoard);
        // signal that boarding is not allowed and cars
        // should wait for the next ferry
        pthread_mutex_lock(&mutex);
        isFerryPresent = false;
        isFerryTravelling = true;
        numOfCars -= numOfCarsOnBoard;
        pthread_mutex_unlock(&mutex);
        // go to antirio
        sleep(2); // travel time
        printf("Ferry has reached Antirio!\n");
        pthread_mutex_lock(&mutex);
        isFerryTravelling = false;
        pthread_mutex_unlock(&mutex);
    }
    pthread_exit(NULL);
}

void parseCarArg(int argc, char *argv[])
{
    int i;
    for (i = 0; i < argc; i++)
    {
        if (strcmp(argv[i], "-c") == 0)
        {
            if (++i < argc && strlen(argv[i]) > 0)
                numOfCars = strtol(argv[i], NULL, 10); // convert to long
            if (numOfCars == 0)
            {
                perror("You must enter a number of cars > 0!\n");
                exit(EXIT_FAILURE);
            }
            break;
        }
    }
}

int main(int argc, char *argv[])
{
    if (argc == 0)
        exit(EXIT_FAILURE);
    parseCarArg(argc, argv);
    srand(time(NULL)); // seed the generator using epoch time in millis

    if (sem_init(&sem, 0, MAX_FERRY_CAP) == -1) // up to 20 cars can board at a time
    {
        perror("Failed to initialize semaphore!\n");
        exit(EXIT_FAILURE);
    }

    if (pthread_mutex_init(&mutex, NULL) != 0)
    {
        perror("Failed to initialize mutex!\n");
        exit(EXIT_FAILURE);
    }

    pthread_t cars[numOfCars];
    int i;
    for (i = 0; i < numOfCars; i++)
    {
        int *id = malloc(sizeof(int));
        *id = i;
        if (pthread_create(&cars[i], NULL, embark, id) != 0)
        {
            perror("Failed to create threads for the cars!\n");
            exit(EXIT_FAILURE);
        }
    }

    // ferry setup
    pthread_t ferry;
    pthread_create(&ferry, NULL, initFerrySchedule, NULL);
    pthread_join(ferry, NULL);

    // wait for all threads to finish
    for (i = 0; i < numOfCars; i++)
        pthread_join(cars[i], NULL);
    sem_destroy(&sem);
    pthread_mutex_destroy(&mutex);
    return 0;
}