#include <iostream>#include <thread>#include <mutex>#include <chrono>#include <semaphore>std::array<std::mutex, 5> forks;std::counting_semaphore<4> room(4);void think(int philosopherIndex) { // Simulate thinking std::cout << "Philosopher " << philosopherIndex << " is thinking." << std::endl; std::this_thread::sleep_for(std::chrono::milliseconds(100));}void eat(int philosopherIndex) { // Simulate eating std::cout << "Philosopher " << philosopherIndex << " is eating." << std::endl; std::this_thread::sleep_for(std::chrono::milliseconds(100));}void philosopher(int i) { while (true) { think(i); room.acquire(); // Wait for available seat in the room forks[i].lock(); // Wait for left fork forks[(i + 1) % 5].lock(); // Wait for right fork eat(i); forks[(i + 1) % 5].unlock(); // Release right fork forks[i].unlock(); // Release left fork room.release(); // Leave the room }}int main() { std::array<std::thread, 5> philosopherThreads; for (int i = 0; i < 5; ++i) { philosopherThreads[i] = std::thread(philosopher, i); } for (int i = 0; i < 5; ++i) { philosopherThreads[i].join(); } return 0;}
管程方案
#include <iostream>#include <thread>#include <mutex>#include <condition_variable>#include <chrono>class DiningController {public: void getForks(int pid) { int left = pid; int right = (pid + 1) % 5; std::unique_lock<std::mutex> lock(mutex); if (!fork[left]) forkReady[left].wait(lock); // Queue on condition variable fork[left] = false; if (!fork[right]) forkReady[right].wait(lock); // Queue on condition variable fork[right] = false; } void releaseForks(int pid) { int left = pid; int right = (pid + 1) % 5; std::unique_lock<std::mutex> lock(mutex); if (forkReady[left].empty()) // No one is waiting for this fork fork[left] = true; else forkReady[left].notify_one(); // Awaken a process waiting on this fork if (forkReady[right].empty()) // No one is waiting for this fork fork[right] = true; else forkReady[right].notify_one(); // Awaken a process waiting on this fork }private: std::mutex mutex; std::array<std::condition_variable, 5> forkReady; std::array<bool, 5> fork = {true, true, true, true, true};};DiningController controller;void philosopher(int pid) { while (true) { std::cout << "Philosopher " << pid << " is thinking." << std::endl; std::this_thread::sleep_for(std::chrono::milliseconds(100)); controller.getForks(pid); std::cout << "Philosopher " << pid << " is eating." << std::endl; std::this_thread::sleep_for(std::chrono::milliseconds(100)); controller.releaseForks(pid); }}int main() { std::array<std::thread, 5> philosopherThreads; for (int i = 0; i < 5; ++i) { philosopherThreads[i] = std::thread(philosopher, i); } for (int i = 0; i < 5; ++i) { philosopherThreads[i].join(); } return 0;}
impl in C
#include <pthread.h>#include <semaphore.h>#include <stdio.h>#define N 5#define THINKING 2#define HUNGRY 1#define EATING 0#define LEFT (phnum + 4) % N #define RIGHT (phnum + 1) % N int state[N]; int phil[N] = { 0, 1, 2, 3, 4 }; sem_t mutex; sem_t S[N]; void test(int phnum) { if (state[phnum] == HUNGRY && state[LEFT] != EATING && state[RIGHT] != EATING) { // state that eating state[phnum] = EATING; sleep(2); printf("Philosopher %d takes fork %d and %d\n", phnum + 1, LEFT + 1, phnum + 1); printf("Philosopher %d is Eating\n", phnum + 1); // sem_post(&S[phnum]) has no effect // during takefork // used to wake up hungry philosophers // during putfork sem_post(&S[phnum]); } } // take up chopsticks void take_fork(int phnum) { sem_wait(&mutex); // state that hungry state[phnum] = HUNGRY; printf("Philosopher %d is Hungry\n", phnum + 1); // eat if neighbours are not eating test(phnum); sem_post(&mutex); // if unable to eat wait to be signalled sem_wait(&S[phnum]); sleep(1); } // put down chopsticks void put_fork(int phnum) { sem_wait(&mutex); // state that thinking state[phnum] = THINKING; printf("Philosopher %d putting fork %d and %d down\n", phnum + 1, LEFT + 1, phnum + 1); printf("Philosopher %d is thinking\n", phnum + 1); test(LEFT); test(RIGHT); sem_post(&mutex); } void* philospher(void* num) { while (1) { int* i = num; sleep(1); take_fork(*i); sleep(0); put_fork(*i); } } int main() { int i; pthread_t thread_id[N]; // initialize the semaphores sem_init(&mutex, 0, 1); for (i = 0; i < N; i++) sem_init(&S[i], 0, 0); for (i = 0; i < N; i++) { // create philosopher processes pthread_create(&thread_id[i], NULL, philospher, &phil[i]); printf("Philosopher %d is thinking\n", i + 1); } for (i = 0; i < N; i++) pthread_join(thread_id[i], NULL); }