问题描述

C++ 关于哲学家进餐问题求教？？

#include<Windows.h>
#include<iostream>
#include<string>
#include<thread>
#include<mutex>
using namespace std;

std::mutex  mu;
std::mutex chopsticks[5];

const char THINKING = 0;
const char WAITING = 1;
const char EATING = 2;

class philosopher {
public:
    philosopher(int n) { status = THINKING; number = n; }
    ~philosopher() { };

    int can_eat() {
        philosopher left = philosopher((number + 1) % 5);
        philosopher right = philosopher((number + 4) % 5);
        if (left.get_status() != EATING   &&  right.get_status() != EATING   &&   status==WAITING)
            return 1;
        return 0;
    }

    void eat() {
        chopsticks[number % 5].lock();
        chopsticks[(number + 1) % 5].lock();
        status = EATING;
        Sleep(1000);
    }

    void put_down_chopsticks() {
        status = THINKING;
        chopsticks[number % 5].unlock();
        chopsticks[(number + 1) % 5].unlock();
    }

    int get_status() { return status; }
    int get_number() { return number; }
    void set_status(int s) { status = s; }

private:
    int status;
    int  number;
};

philosopher* ph_1 = new philosopher(0);
philosopher* ph_2 = new philosopher(1);
philosopher* ph_3 = new philosopher(2);
philosopher* ph_4 = new philosopher(3);
philosopher* ph_5 = new philosopher(4);

void show() {
    mu.lock();
    cout << "===============" << endl;
    cout << ph_1->get_number() << ":" << ph_1->get_status() << endl;
    cout << ph_2->get_number() << ":" << ph_2->get_status() << endl;
    cout << ph_3->get_number() << ":" << ph_3->get_status() << endl;
    cout << ph_4->get_number() << ":" << ph_4->get_status() << endl;
    cout << ph_5->get_number() << ":" << ph_5->get_status() << endl;
    mu.unlock();
}

void try_to_eat(philosopher *p) {
    while (1) {
        switch (p->get_status()) {
        case   THINKING:
            Sleep(2000);
            p->set_status(WAITING);
            break;
        case WAITING:
            if (p->can_eat())
            {
                p->eat();
            }
            else{
                p->set_status(WAITING);
            }
            break;
        case EATING:
            p->put_down_chopsticks();
            break;
        default:
            break;
        }
        show();
    }
}

int main() {
    std::thread t1(try_to_eat, ph_1);
    std::thread t2(try_to_eat, ph_2);
    std::thread t3(try_to_eat, ph_3);
    std::thread t4(try_to_eat, ph_4);
    std::thread t5(try_to_eat, ph_5);
    show();
    t1.join();
    t2.join();
    t3.join();
    t4.join();
    t5.join();
    return 0;
}

解决方案

操作系统并发和互斥：哲学家进餐问题和理发师问题?

1． 哲学家进餐问题：?
(1) 在什么情况下5 个哲学家全部吃不上饭？?
考虑两种实现的方式，如下：?
A.?
算法描述：?
void philosopher(int i) /*i：哲学家编号，从0 到4*/?
{?
while (TRUE) {?
think( ); /*哲学家正在思考*/?
take_fork(i)......
答案就在这里：关于哲学家进餐问题

解决方案二：

你想问的问题呢？这段程序有什么不对吗？