dining-philosophers/DiningPhilosophers.c

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

#define THINKING    0           /*philosopher is thinking*/
#define HUNGRY      1           /*philosopher is trying to get forks*/
#define EATING      2           /*philosopher is eating*/
// pthread_mutex_t mutex;            /*mutual exclusion for critical region*/


typedef struct PhilosopherData {
    int eatingCount;
    int position;
    sem_t semaphore;
    int state;
    pthread_t thread;
} PhilosopherData;

bool AllPhilosophersFull(PhilosopherData PhilosopherList[], int numPhilosophers);
void Down(sem_t* semaphore);
void Eat(PhilosopherData* philosopherSelected);
int GetPhilosopherCount(char* argv);
void* Philosopher(void* philosopherPassed);
void PhilosopherInit(int philosopherTotal);
void PhilosopherListInit(PhilosopherData PhilosopherList[], int philosopherTotal);
void PutForks(PhilosopherData* philosopherSelected);
void TakeForks(PhilosopherData* philosopherSelected);
bool PhilosopherCanEat(PhilosopherData PhilosopherList[], int selectedPosition, int philosopherTotal);
void Think(PhilosopherData* philosopherSelected);
void Up(sem_t* semaphore);

/*
 *  Todo:
 *      Fix each function's requirements
 *  Theories:
 *      Threads should be put to sleep if can't eat
 *      Sleep has to be awoken by something else, process can't wake own thread
 *      Place semaphores so states can be checked by all
 *      Total fork count = N / 2
 */

int main(int argc, char* argv[]) 
{
    if (argc < 2)
        printf("Too few arguments, exiting...\n");
    if (argc > 2)
        printf("Too many arguments, exiting...\n");
    if (argc == 2)
    {
        int philosopherTotal;
        philosopherTotal = GetPhilosopherCount(argv[1]);
        PhilosopherInit(philosopherTotal);    
    }
    return 0;
}

// Takes in array of times each philosopher has eaten
// If all philosophers have ate twice, then returns true
// Otherwise, if a philosopher has not eaten twice, returns false
bool AllPhilosophersFull(PhilosopherData PhilosopherList[], int numPhilosophers)
{
    for (int i = 0; i < numPhilosophers; i++)
        if (PhilosopherList[i].eatingCount < 2)
            return false;
    return true;
}

//  Takes a pointer to a philosopher and puts semaphore into waiting state.
//  TODO:
//      Turn function into picking up forks (starting waits)
//      (Right fork is owned by selectedPhilosopher number for consistency)
//      Add sem_wait
void Down(sem_t* semaphore)
{
    sem_wait(semaphore);
    printf("A semaphore was put into waiting...\n");
}

// Sets philosopher to eating state and increments eating count.
void Eat(PhilosopherData* philosopherSelected)
{
    printf("Philosopher %d is eating...\n", philosopherSelected->position);
    philosopherSelected->state = EATING;
    ++philosopherSelected->eatingCount;
}

// Converts char* to number.
int GetPhilosopherCount(char* argv)
{
    int philosopherTotal;
    sscanf(argv, "%d", &philosopherTotal);
    return philosopherTotal;
}

//  Main function that each thread runs.
void* Philosopher(void* philosopherPassed)
{
    PhilosopherData *philosopherSelected = (PhilosopherData*) philosopherPassed;
    while (true)
    {
        Think(philosopherSelected);                /*philosopher is thinking*/
        TakeForks(philosopherSelected);          /*acquire two forks or block*/
        Eat(philosopherSelected);                  /*yum-yum, spaghetti*/
        PutForks(philosopherSelected);           /*put both forks back on table*/
        break;
    }
}

//  Handles all philosopher threads, finishes when all philosophers are full.
void PhilosopherInit(int philosopherTotal)
{
    PhilosopherData PhilosopherList[philosopherTotal];
    PhilosopherListInit(PhilosopherList, philosopherTotal);
    while (!AllPhilosophersFull(PhilosopherList, philosopherTotal))
    {
        for (int i = 0; i < philosopherTotal; i++)
        {
            if (PhilosopherCanEat(PhilosopherList, i, philosopherTotal))
            {
                Up(&(PhilosopherList[i-1].semaphore));
                Up(&(PhilosopherList[i].semaphore));
            }
        }
    }
}

void PhilosopherListInit(PhilosopherData PhilosopherList[], int philosopherTotal)
{
    for (int i = 0; i < philosopherTotal; i++)
    {
        PhilosopherList[i].position = i;
        PhilosopherList[i].eatingCount = 0;
        sem_init(&PhilosopherList[i].semaphore, 0, 1);
        pthread_create(&PhilosopherList[i].thread, NULL, &Philosopher, &PhilosopherList[i]);
        pthread_join(PhilosopherList[i].thread, NULL);
    }
}

void PutForks(PhilosopherData* philosopherSelected)
{
    printf("Philosopher %d is putting forks down...\n", philosopherSelected->position);
    // Down(&mutex);               /*enter critical region*/
    // philosopherState[selectedPhilosopher] = THINKING;        /*record fact that philosopher i is hungry*/
    // Test(selectedPhilosopher, numPhilosophers);
    // Test(LEFT);                 /*try to acquire 2 forks*/
    // Test(RIGHT);                /*exit critical region*/
    // Up(&mutex);                 /*block if forks were not acquired*/
}

//  Philosopher takes the forks on the left and right.
void TakeForks(PhilosopherData* philosopherSelected)
{
    printf("Philosopher %d is taking forks...\n", philosopherSelected->position);
    Down(&philosopherSelected->semaphore);
    // Down(&mutex);               /*enter critical region*/
    // PhilosopherList.state = HUNGRY;          /*philosopher has finished eating*/
    // Test(selectedPhilosopher, );                    /*see if left neighbor can now eat*/
    // Up(&mutex);                 /*see if right neighbor can now eat*/
    // Down(&philosopherSemaphore[selectedPhilosopher]);                /*exit critical region*/
}

//  If philosopher is hungry and forks are free, then returns true.
//  Else, philosopher returns false.
//  Left philosopher math: (i+N-1)%N    Right philosopher math: (i+1)%N
bool PhilosopherCanEat(PhilosopherData PhilosopherList[], int selectedPosition, int philosopherTotal)
{
    if (PhilosopherList[selectedPosition].state != HUNGRY)
        return false;
    int leftPhilosopher = (selectedPosition + (philosopherTotal-1)) % philosopherTotal;
    int rightPhilosopher = (selectedPosition + 1) % philosopherTotal;
    if (PhilosopherList[leftPhilosopher].state == EATING)
        return false;
    if (PhilosopherList[rightPhilosopher].state == EATING)
        return false;
    return true;
}

void Think(PhilosopherData* philosopherSelected)
{
    // printf("%d is now thinking.\n", PhilosopherList.position);
    // PhilosopherList.state = THINKING;          /*philosopher has finished eating*/
    philosopherSelected->state = THINKING;
    printf("Philosopher %d is thinking...\n", philosopherSelected->position);
}

// Todo:
//      Make function release hold on semaphore
//      Use 'sem_post'
void Up(sem_t* semaphore)
{
    sem_post(semaphore);
    printf("A semaphore was released...\n");
}