哲学家进餐问题

philosopher.c

// gcc -std=c99 -g philosopher.c -o philosopher
#include <pthread.h>
#include <unistd.h>
#include <stdio.h>
#include <stdbool.h>

struct philosopher {
    int id;
    int think_count;
    bool eating;
    struct philosopher *left;
    struct philosopher *right;
    pthread_mutex_t *pmutex;
    pthread_cond_t cond;
    pthread_t tid;
};

void *think(void *arg)
{
    struct philosopher *pher = (struct philosopher *)arg;
    pthread_mutex_t *pmutex = pher->pmutex;
    pthread_mutex_lock(pmutex);

    pher->eating = false;
    pthread_cond_signal(&pher->left->cond);
    pthread_cond_signal(&pher->right->cond);

    pthread_mutex_unlock(pmutex);

    (pher->think_count)++;
    if (pher->think_count % 10 == 0) {
        printf("philosopher %d has thought %d times.\n", pher->id, pher->think_count);
    }

    sleep(1);
}

void *eat(void *arg)
{
    struct philosopher *pher = (struct philosopher *)arg;
    pthread_mutex_t *pmutex = pher->pmutex;
    pthread_mutex_lock(pmutex);

    while (pher->left->eating || pher->right->eating) {
        pthread_cond_wait(&pher->cond, pmutex);
    }

    pher->eating = true;

    pthread_mutex_unlock(pmutex);

    sleep(1);
}

void *run(void *arg)
{
    struct philosopher *pher = (struct philosopher *)arg;
    while (true) {
        printf("run. id:%d\n", pher->id);
        think(arg);
        eat(arg);
    }
    return NULL;
}

int main()
{
    pthread_mutex_t mutex;
    pthread_mutex_init(&mutex, NULL);

    pthread_attr_t attr;
    pthread_attr_init(&attr);
    pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);

    struct philosopher phers[5];
    for (int i=0; i<5; i++) {
        phers[i].id = i;
        phers[i].think_count = 0;
        phers[i].eating = false;
        phers[i].left = &phers[(i+4)%5];
        phers[i].right = &phers[(i+1)%5];
        phers[i].pmutex = &mutex;
        pthread_cond_init(&phers[i].cond, NULL);
        pthread_create(&phers[i].tid, &attr, run, &phers[i]);
        pthread_join(phers[i].tid, NULL);
    }

    while (true) {
        sleep(1);
    }

    pthread_mutex_destroy(&mutex);
    pthread_attr_destroy(&attr);
    return 0;
}