Python实现哲学家就餐问题

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哲学家就餐问题：

哲学家就餐问题是典型的同步问题，该问题描述的是五个哲学家共用一张圆桌，分别坐在五张椅子上，在圆桌上有五个盘子和五个叉子（如下图），他们的生活方式是交替的进行思考和进餐，思考时不能用餐，用餐时不能思考。平时，一个哲学家进行思考，饥饿时便试图用餐，只有在他同时拿到他的盘子左右两边的两个叉子时才能进餐。进餐完毕后，他会放下叉子继续思考。请写出代码来解决如上的哲学家就餐问题，要求代码返回“当每个哲学家分别需要进食 n 次”时这五位哲学家具体的行为记录。

测试用例：

输入：n = 1 （1<=n<=60，n 表示每个哲学家需要进餐的次数。）

预期输出：

[[4,2,1],[4,1,1],[0,1,1],[2,2,1],[2,1,1],[2,0,3],[2,1,2],[2,2,2],[4,0,3],[4,1,2],[0,2,1],[4,2,2],[3,2,1],[3,1,1],[0,0,3],[0,1,2],[0,2,2],[1,2,1],[1,1,1],[3,0,3],[3,1,2],[3,2,2],[1,0,3],[1,1,2],[1,2,2]]

思路:

输出列表中的每一个子列表描述了某个哲学家的具体行为，它的格式如下：
output[i] = [a, b, c] (3 个整数)

• a 哲学家编号。
• b 指定叉子：{1 : 左边, 2 : 右边}.
• c 指定行为：{1 : 拿起, 2 : 放下, 3 : 吃面}。
  如 [4,2,1] 表示 4 号哲学家拿起了右边的叉子。所有自列表组合起来，就完整描述了“当每个哲学家分别需要进食 n 次”时这五位哲学家具体的行为记录。

代码实现

import queue
import threading
import time
import randomclass CountDownLatch:def __init__(self, count):self.count = countself.condition = threading.Condition()def wait(self):try:self.condition.acquire()while self.count > 0:self.condition.wait()finally:self.condition.release()def count_down(self):try:self.condition.acquire()self.count -= 1self.condition.notifyAll()finally:self.condition.release()class DiningPhilosophers(threading.Thread):def __init__(self, philosopher_number, left_fork, right_fork, operate_queue, count_latch):super().__init__()self.philosopher_number = philosopher_numberself.left_fork = left_forkself.right_fork = right_forkself.operate_queue = operate_queueself.count_latch = count_latchdef eat(self):time.sleep(0.01)self.operate_queue.put([self.philosopher_number, 0, 3])def think(self):time.sleep(random.random())def pick_left_fork(self):self.operate_queue.put([self.philosopher_number, 1, 1])def pick_right_fork(self):self.operate_queue.put([self.philosopher_number, 2, 1])def put_left_fork(self):self.left_fork.release()self.operate_queue.put([self.philosopher_number, 1, 2])def put_right_fork(self):self.right_fork.release()self.operate_queue.put([self.philosopher_number, 2, 2])def run(self):while True:left = self.left_fork.acquire(blocking=False)right = self.right_fork.acquire(blocking=False)if left and right:self.pick_left_fork()self.pick_right_fork()self.eat()self.put_left_fork()self.put_right_fork()breakelif left and not right:self.left_fork.release()elif right and not left:self.right_fork.release()else:time.sleep(0.01)print(str(self.philosopher_number) + ' count_down')self.count_latch.count_down()if __name__ == '__main__':operate_queue = queue.Queue()fork1 = threading.Lock()fork2 = threading.Lock()fork3 = threading.Lock()fork4 = threading.Lock()fork5 = threading.Lock()n = 1latch = CountDownLatch(5 * n)for _ in range(n):philosopher0 = DiningPhilosophers(0, fork5, fork1, operate_queue, latch)philosopher0.start()philosopher1 = DiningPhilosophers(1, fork1, fork2, operate_queue, latch)philosopher1.start()philosopher2 = DiningPhilosophers(2, fork2, fork3, operate_queue, latch)philosopher2.start()philosopher3 = DiningPhilosophers(3, fork3, fork4, operate_queue, latch)philosopher3.start()philosopher4 = DiningPhilosophers(4, fork4, fork5, operate_queue, latch)philosopher4.start()latch.wait()queue_list = []for i in range(5 * 5 * n):queue_list.append(operate_queue.get())print(queue_list)

 

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