哲学家就餐问题

kedobi

引入服务生解法之后只有偶数项的进程能够拿到两个叉子

有办法能让奇数进程也能拿到叉子吗

# -*- coding:utf-8 -*-
import threading
from time import sleep


numPhilosophers = numForks = 10

class Philosopher(threading.Thread):
    def __init__(self, index):
        threading.Thread.__init__(self)
        self.index = index
        self.leftFork = forks[self.index]
        self.rightFork = forks[(self.index + 1) % numForks]

    def run(self):
        while True:
           if waiter.serve(self):
               self.dining()
               waiter.clean(self)
        self.thinking()

    def dining(self):
        print ("Philosopher", self.index, " starts to eat.") 
        sleep(1/1000)
        print ("Philosopher", self.index, " finishes eating and leaves to think.")
    def thinking(self):
        sleep(1/100)

class Fork():
    def __init__(self, index):
        self.index = index
        self._lock = threading.Lock()

    def pickup(self):
        self._lock.acquire() #申请锁定进程

    def putdown(self):
        self._lock.release() #释放进程

class Waiter:
    def __init__(self):
        self.forks = [Fork(idx) for idx in range(numForks)]
            #最开始餐叉还没有被分配给任何人，所以全部 False
        self.forks_using = [False] * numForks

        #如果哲学家的左右餐叉都是空闲状态，就为这位哲学家服务提供餐叉
    def serve(self, philor):
        if not self.forks_using[philor.leftFork.index] and not self.forks_using[philor.rightFork.index]:
            self.forks_using[philor.leftFork.index] = True
            self.forks_using[philor.rightFork.index] = True
            self.forks[philor.leftFork.index].pickup()
            self.forks[philor.rightFork.index].pickup()
            return True
        else:
            return False        

        #哲学家用餐完毕后，清理并回收餐叉
    def clean(self, philor):
        self.forks[philor.leftFork.index].putdown()
        self.forks[philor.rightFork.index].putdown()
        self.forks_using[philor.leftFork.index] = False
        self.forks_using[philor.rightFork.index] = False


if __name__ == '__main__':
        #创建服务生与哲学家实例
    waiter = Waiter()
    forks = [Fork(idx) for idx in range(numForks)]
    philosophers = [Philosopher(idx) for idx in range(numPhilosophers)]

        #开启所有的哲学家线程
    for philosopher in philosophers:
        philosopher.start()

        # 方便 CTRL + C 退出程序
    try:
        while True: sleep(0.1)
    except Exception:
        raise e

kedobi

运行环境py3.5