宁波哪里做网站的,网站系统功能描述,做网站走啥科目,惠州网站建设方案外包哲学家就餐问题 问题信号量实现发生死锁版限制人数版规定取筷顺序 条件变量实现 问题 在一个圆桌上坐着五位哲学家#xff0c;每个哲学家面前有一个碗装有米饭的碗和一个筷子。哲学家的生活包括思考和进餐两个活动。当一个哲学家思考时#xff0c;他不需要任何资源。当他饿了… 哲学家就餐问题 问题信号量实现发生死锁版限制人数版规定取筷顺序 条件变量实现 问题 在一个圆桌上坐着五位哲学家每个哲学家面前有一个碗装有米饭的碗和一个筷子。哲学家的生活包括思考和进餐两个活动。当一个哲学家思考时他不需要任何资源。当他饿了时他试图拿起两只相邻的筷子来吃饭。由于碗和筷子不能被共享因此必须找到一种方法来确保哲学家能够安全地进餐即不会发生死锁所有哲学家都在等待筷子也不会发生饥饿某些哲学家永远无法拿起筷子 信号量实现
发生死锁版
#include pthread.h
#include semaphore.h
#include vector
#include unistd.h
#include iostream#define N 5
#define P(x) sem_wait(x)
#define V(x) sem_post(x)sem_t mutex_table;
std::vectorsem_t mutex_chopsticks(N);void* T_philosopher(void* arg) {int id *((int*)arg);// id哲学家吃饭需要的2根筷子int lhs (id N - 1) % N;int rhs id % N;while (true) {P(mutex_chopsticks[lhs]);printf( %d by T%d\n, lhs, id);P(mutex_chopsticks[rhs]);printf( %d by T%d\n, rhs, id);// Eat.// Philosophers are allowed to eat in parallel.printf(- %d by T%d\n, lhs, id);printf(- %d by T%d\n, rhs, id);V(mutex_chopsticks[lhs]);V(mutex_chopsticks[rhs]);sleep(0.5);}
}int main() {for (int i 0; i N; i) {sem_init(mutex_chopsticks[i], 0, 1);}std::vectorpthread_t threads(N);std::vectorint ids(N);for (int i 0; i N; i) {ids[i] i 1;pthread_create(threads[i], nullptr, T_philosopher, ids[i]);}for (int i 0; i N; i) {pthread_join(threads[i], nullptr);}
}限制人数版
限制最多只能4人同时上桌, 则可以保证至少有一个人可以同时拿起两根筷子
#include pthread.h
#include semaphore.h
#include vector
#include unistd.h
#include iostream#define P(x) sem_wait(x)
#define V(x) sem_post(x)const int N 5;sem_t mutex_table;
std::vectorsem_t mutex_chopsticks(N);void* T_philosopher(void* arg) {int id *((int*)arg);// id哲学家吃饭需要的2根筷子int lhs (id N - 1) % N;int rhs id % N;while (true) {// Come to mutex_tableP(mutex_table);P(mutex_chopsticks[lhs]);printf( %d by T%d\n, lhs, id);P(mutex_chopsticks[rhs]);printf( %d by T%d\n, rhs, id);// Eating// Philosophers are allowed to eat in parallel.printf(- %d by T%d\n, lhs, id);printf(- %d by T%d\n, rhs, id);V(mutex_chopsticks[lhs]);V(mutex_chopsticks[rhs]);// Leave mutex_tableV(mutex_table);// Thinkingsleep(0.5);}
}int main() {// 保证任何实际最多只有4个人在桌子上// 这样至少有1个人可以拿到2根筷子sem_init(mutex_table, 0, N - 1);for (int i 0; i N; i) {sem_init(mutex_chopsticks[i], 0, 1);}std::vectorpthread_t threads(N);std::vectorint ids(N);for (int i 0; i N; i) {ids[i] i 1;pthread_create(threads[i], nullptr, T_philosopher, ids[i]);}for (int i 0; i N; i) {pthread_join(threads[i], nullptr);}
}规定取筷顺序
规定每个人, 先拿编号小的筷子, 再拿编号大的筷子
#include pthread.h
#include semaphore.h
#include vector
#include unistd.h
#include iostream#define P(x) sem_wait(x)
#define V(x) sem_post(x)const int N 5;sem_t mutex_table;
std::vectorsem_t mutex_chopsticks(N);void* T_philosopher(void* arg) {int id *((int*)arg);// id哲学家吃饭需要的2根筷子int lhs (id N - 1) % N;int rhs id % N;while (true) {// 规定每个人, 先拿编号小的筷子, 再拿编号大的筷子if (lhs rhs) {P(mutex_chopsticks[lhs]);P(mutex_chopsticks[rhs]);} else {P(mutex_chopsticks[rhs]);P(mutex_chopsticks[lhs]);}printf( %d by T%d\n, lhs, id);printf( %d by T%d\n, rhs, id);// Eatingprintf(- %d by T%d\n, lhs, id);printf(- %d by T%d\n, rhs, id);V(mutex_chopsticks[lhs]);V(mutex_chopsticks[rhs]);// Thinkingsleep(0.5);}
}int main() {for (int i 0; i N; i) {sem_init(mutex_chopsticks[i], 0, 1);}std::vectorpthread_t threads(N);std::vectorint ids(N);for (int i 0; i N; i) {ids[i] i 1;pthread_create(threads[i], nullptr, T_philosopher, ids[i]);}for (int i 0; i N; i) {pthread_join(threads[i], nullptr);}
}
条件变量实现
#include pthread.h
#include vector
#include unistd.h
#include iostream#define Lock(x) pthread_mutex_lock(x)
#define UnLock(x) pthread_mutex_unlock(x)const int N 5;pthread_mutex_t mutex PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t cond PTHREAD_COND_INITIALIZER;
std::vectorint available(N, true);void* T_philosopher(void* arg) {int id *((int*)arg);// id哲学家吃饭需要的2根筷子int lhs (id N - 1) % N;int rhs id % N;while (true) {// Come to mutex_tableLock(mutex);while (!(available[lhs] available[rhs])) {pthread_cond_wait(cond, mutex);}printf( %d by T%d\n, lhs, id);printf( %d by T%d\n, rhs, id);available[lhs] available[rhs] false;UnLock(mutex);// Eatingsleep(0.5);printf(- %d by T%d\n, lhs, id);printf(- %d by T%d\n, rhs, id);available[lhs] available[rhs] true;pthread_cond_broadcast(cond);// Thinkingsleep(0.5);}
}int main() {std::vectorpthread_t threads(N);std::vectorint ids(N);for (int i 0; i N; i) {ids[i] i 1;pthread_create(threads[i], nullptr, T_philosopher, ids[i]);}for (int i 0; i N; i) {pthread_join(threads[i], nullptr);}
}
