식사하는 철학자

#include <stdio.h>       

#include <pthread.h>   

 

#define NUM_THREADS 5

 

pthread_mutex_t mutexes[NUM_THREADS];

pthread_cond_t conditionVars[NUM_THREADS];

 

int permits[NUM_THREADS];

pthread_t tids[NUM_THREADS];

 

void pickup_forks(int philosopher_number) {

    pthread_mutex_lock(&mutexes[philosopher_number%NUM_THREADS]);

    while (permits[philosopher_number%NUM_THREADS] == 0) {

        pthread_cond_wait(&conditionVars[philosopher_number%NUM_THREADS], &mutexes[philosopher_number%NUM_THREADS]);

    }

    permits[philosopher_number%NUM_THREADS] = 0;

    pthread_mutex_unlock(&mutexes[philosopher_number%NUM_THREADS]);

}

 

void return_forks(int philosopher_number) {

    pthread_mutex_lock(&mutexes[philosopher_number%NUM_THREADS]);

    permits[philosopher_number%NUM_THREADS] = 1;

    pthread_cond_signal(&conditionVars[philosopher_number%NUM_THREADS]);

    pthread_mutex_unlock(&mutexes[philosopher_number%NUM_THREADS]);

     

}

 

void* Philosopher(void * arg) {

    int philosopher_number;

    philosopher_number = (int)arg;

 

    // pickup left fork

    pickup_forks(philosopher_number);

    printf("philosopher(%d) picks up the fork(%d).\n", philosopher_number, philosopher_number);

     

    // pickup right fork

    pickup_forks(philosopher_number+1);

    printf("philosopher(%d) picks up the fork(%d).\n", philosopher_number, (philosopher_number + 1) % NUM_THREADS);

     

    printf("philosopher(%d) starts eating \n", philosopher_number);

    sleep(2);

    printf("philosopher(%d) finishes eating \n", philosopher_number);

 

    // putdown right fork

    return_forks(philosopher_number + 1);

    printf("philosopher(%d) put down the fork(%d).\n", philosopher_number, (philosopher_number + 1) % NUM_THREADS);

 

    // putdown left fork

    return_forks(philosopher_number);

    printf("philosopher(%d) put down the fork(%d).\n", philosopher_number, philosopher_number);

 

    return NULL;

}

 

void * OddPhilosopher(void * arg) {

    int philosopher_number;

    philosopher_number = (int)arg;

 

    // pickup right fork

    pickup_forks(philosopher_number + 1);

    printf("philosopher(%d) picks up the fork(%d).\n", philosopher_number, (philosopher_number + 1) % NUM_THREADS);

 

    // pickup left fork

    pickup_forks(philosopher_number);

    printf("philosopher(%d) picks up the fork(%d).\n", philosopher_number, philosopher_number);

 

    printf("philosopher(%d) starts eating \n", philosopher_number);

    sleep(2);

    printf("philosopher(%d) finishes eating \n", philosopher_number);

 

    // putdown left fork

    return_forks(philosopher_number);

    printf("philosopher(%d) puts down the fork(%d).\n", philosopher_number, philosopher_number);

 

    // putdown right fork

    return_forks(philosopher_number + 1);

    printf("philosopher(%d) puts down the fork(%d).\n", philosopher_number, (philosopher_number + 1) % NUM_THREADS);

 

    return NULL;

}

 

int main() {

    int i;

 

    for (i = 0; i < NUM_THREADS; i++) {

        pthread_mutex_init(&mutexes[i], NULL);

        pthread_cond_init(&conditionVars[i], NULL);

        permits[i] = 1;

    }

 

    for (i = 0; i < NUM_THREADS; i++) {

        if (i % 2) {

            pthread_create(&tids[i], NULL, OddPhilosopher, (void*)(i));

        }

        else{

            pthread_create(&tids[i], NULL, Philosopher, (void*)(i));

        }

    }

 

    for (i = 0; i < NUM_THREADS; i++) {

        pthread_join(tids[i], NULL);

    }

 

    for (i = 0; i < NUM_THREADS; i++) {

        pthread_mutex_destroy(&mutexes[i]);

        pthread_cond_destroy(&conditionVars[i]);

    }

 

    return 0;

}