Socrates and Plato sit down for dinner

philosophers.c

/* Compile as gcc philosophers.c -pthread */

#include <stdio.h>
#include <pthread.h>
#include <unistd.h>

pthread_mutex_t fork_ = PTHREAD_MUTEX_INITIALIZER;
pthread_mutex_t knife = PTHREAD_MUTEX_INITIALIZER;

void *socrates(void *nothing) {
    (void) nothing;

    /* Comment out the next two lines... */
    pthread_mutex_lock(&fork_);
    printf("Socrates has picked up his fork.\n");
    pthread_mutex_lock(&knife);
    printf("Socrates has picked up his knife.\n");
    /* and uncomment these two lines
    pthread_mutex_lock(&fork_);
    printf("Socrates has picked up his fork.\n");
    */
    printf("Socrates dines.\n");
    pthread_mutex_unlock(&fork_);
    printf("Socrates has set down his fork.\n");
    pthread_mutex_unlock(&knife);
    printf("Socrates has set down his fork.\n");

    return NULL;
}

void *plato(void *nothing) {
    (void) nothing;

    pthread_mutex_lock(&fork_);
    printf("Plato has picked up his fork.\n");
    pthread_mutex_lock(&knife);
    printf("Plato has picked up his knife.\n");
    printf("Plato dines.\n");
    pthread_mutex_unlock(&fork_);
    printf("Plato has set down his fork.\n");
    pthread_mutex_unlock(&knife);
    printf("Plato has set down his knife.\n");

    return NULL;
}

int main() {
    pthread_t a;
    pthread_t b;

    pthread_create(&a, NULL, socrates, NULL);
    pthread_create(&b, NULL, plato, NULL);

    pthread_join(a, NULL);
    pthread_join(b, NULL);

    return 0;
}