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;
} PhilosopherData;

bool AllPhilosophersFull(PhilosopherData PhilosopherList[], int numPhilosophers);
void Down(pthread_mutex_t selectedSemaphore);
void Eat(int selectedPhilosopher);
int GetNumberPhilosophers(char* argv);
void Philosopher(int selectedPhilosopher);
void PutForks(PhilosopherData PhilosopherList);
void TakeForks(PhilosopherData PhilosopherList);
void Test(PhilosopherData PhilosopherList[], int positionSelected, int numPhilosophers);
void Think(int selectedPhilosopher);
void Up(pthread_mutex_t selectedSemaphore);

/*
 *  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)
    {
        int philosopherCount;
        philosopherCount = GetNumberPhilosophers(argv[1]);
        Philosopher(philosopherCount);
    }
    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(pthread_mutex_t selectedSemaphore)
{
    printf("Function Down() was called.\n");
}

// 
//  TODO: 
//      Add changing state to function
//      Add increasing eating count functionality
//
void Eat(int selectedPhilosopher)
{
    printf("Function Eat() was called.\n");
}

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

// 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(int numPhilosophers)
{
    // 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];
    PhilosopherData PhilosopherList[numPhilosophers];
    int forkCount = numPhilosophers / 2;
    while (true)
    {
        Think(0);                /*philosopher is thinking*/
        // TakeForks(0, numPhilosophers);          /*acquire two forks or block*/
        // Eat(0);                  /*yum-yum, spaghetti*/
        // PutForks(0, numPhilosophers);           /*put both forks back on table*/
        break;
    }
}

void PutForks(PhilosopherData PhilosopherList)
{
    // Down(&mutex);               /*enter critical region*/
    printf("%d is now thinking.\n", PhilosopherList.position);
    PhilosopherList.state = THINKING;          /*philosopher has finished eating*/
    // 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 PhilosopherList)
{
    // 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
void Test(PhilosopherData PhilosopherList[], int positionSelected, int numPhilosophers)
{
    if (PhilosopherList[positionSelected].state != HUNGRY)
        return;
    int leftPhilosopher = (positionSelected + (numPhilosophers-1)) % numPhilosophers;
    int rightPhilosopher = (positionSelected + 1) % numPhilosophers;
    if (PhilosopherList[leftPhilosopher].state == EATING)
        return;
    if (PhilosopherList[rightPhilosopher].state == EATING)
        return;
    PhilosopherList[positionSelected].state = EATING;
    // Up(&philosopherSemaphore[selectedPhilosopher]);
}

void Think(int selectedPhilosopher)
{
    printf("Function Think() was called.\n");
}

// Todo:
//      Make function release hold on semaphore
//      Use 'sem_post'
void Up(pthread_mutex_t selectedSemaphore)
{
    printf("Function Up() was called.\n");
}