dining-philosophers/DiningPhilosophers.c

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

// #define N           5           /*number of philosophers*/
// #define LEFT        (i+N-1)%N   /*number of i's left neighbor*/
// #define RIGHT       (i+1)%N     /*number of i's right neighbor*/
#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();
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();

/*
 *  Todo:
 *      Add prints to each state change
 *      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;
}

//
//  TODO:
//      Turn function into picking up forks (starting waits)
//      (Right fork is owned by selectedPhilosopher number for consistency)
//      Add sem_wait
void Down()
{
    printf("Down() was called...\n");
}

// 
//  TODO: 
//      Add changing state to function
//      Add increasing eating count functionality
//
void Eat(PhilosopherData* philosopherSelected)
{
    printf("Philosopher %d is eating...\n", philosopherSelected->position);
    philosopherSelected->state = EATING;
    ++philosopherSelected->eatingCount;
}

// Takes in char* and converts into a number
// Returns a number
int GetPhilosopherCount(char* argv)
{
    int philosopherTotal;
    sscanf(argv, "%d", &philosopherTotal);
    return philosopherTotal;
}

// Takes in the number of philosophers, from 0 to N-1
// Finishes when all philosophers have eaten twice
// TODO:
//      Add splitting function into multiple pthreads
void* Philosopher(void* philosopherPassed)
{
    PhilosopherData *philosopherSelected = (PhilosopherData*) philosopherPassed;
    // Below replaced by PhilosopherData
    // int philosopherEatingCount[numPhilosophers];
    // sem_t philosopherSemaphore[numPhilosophers];                 /*one semaphore per philospher*/
    // // array to keep track of everyone's state
    // int philosopherState[numPhilosophers];
    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;
    }
}

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))
            {
                Down(PhilosopherList[i-1].semaphore);
                Down(PhilosopherList[i].semaphore);
            }
        }
        break;
    }
}

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*/
}

// Takes in a number for a selected philosopher, from 0 to N-1
void TakeForks(PhilosopherData* philosopherSelected)
{
    printf("Philosopher %d is taking forks...\n", philosopherSelected->position);
    sem_wait(&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*/
}

// Takes in the number of philosophers, from 0 to N-1
// Checks if left and right philosopher is not eating,
//      and philosopher is hungry, then philosopher will eat
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()
{
    printf("Up() was called...\n");
}