哲学家就餐问题

# define N 5
# define LEFT (i + N - 1) % N
# define RIGHT (i + 1) % N
# define THINKING 0
# define HUNGRY 1
# define EATING 2
typedef int semaphore;
int state[N];
semaphore mutex = 1;
semaphore s[N];

void philosopher(int i){
    while(TRUE){
        think();
        take_two(i);
        eat();
        put_now(i);
    }
}

void take_two(int i){
    down(&mutex);
    state[i] = HUNGRY;
    test(i);
    up(&mutex);
    down(&s[i]);
}

void put_two(i){
    down(&mutex);
    state[i] = THINKING;
    test(LEFT);
    test(RIGHT);
    up(&mutex);
}

void test(i){               //尝试拿起两把筷子
    if(state[i] == HUNGRY && state[LEFT] != EATING && state[RIGHT] != EATING){
        state[i] = EATING;
        up(&s[i]);
    }
}