day49-2

IPC

(Inter-Process Communication)

Spatial multiplexing memory is isolated from multiple processes can not interact directly

IPC refers to the inter-process communication

Method to realize :

1. Create a shared file

缺点: 效率较低

优点: 理论上交换的数据量可以非常大  

适用于: 交互不频繁  且数据量较大的情况

2. Shared Memory (main mode)

缺点: 数据量不能太大  

优点: 效率高 

适用于: 交互频繁,但是数据量小 

3. Pipeline

管道也是基于文件的    它是单向的   编程比较复杂  

4.socket

编程复杂,更适用于基于网络来交换数据  

The first way of shared memory

• Manger does not write files to achieve grab votes

We can create a container for inter-process synchronization, but does not address security issues, it is not commonly used

from multiprocessing import Process, Lock, Manager


def show(ticket):
    '''查票'''
    print(ticket)
    print('当前剩余票数', ticket['count'])


def buy(ticket):
    '''买票'''
    print(ticket)
    count = ticket['count']

    if count > 0:
        count -= 1
        ticket['count'] = count
        print('抢票成功')
    else:
        print('没有票')


def task(lock, ticket):
    # print(ticket)
    show(ticket)

    lock.acquire()  # 安全问题需要自己另外加锁
    buy(ticket)
    lock.release()




if __name__ == '__main__':
    ticket = {'count': 1}
    m = Manager()
    sync_ticket = m.dict(ticket)
    lock = Lock()

    ps = []
    for i in range(5):
        p = Process(target=task, args=(lock, sync_ticket))
        p.start()
        ps.append(p)
    for p in ps:    # 必须要用join()，否则传入子进程的不是字典，不知道为什么
        p.join()

Note: You must use the join (), otherwise passed in the child process is not a dictionary, and the reason is not clear

Queue

Queue Queue is translated into a special container so special is that the access order of FIFO

It can help us to complete inter-process communication

from multiprocessing import Queue

q = Queue(2) # 创建队列 并且同时只能存储2个元素
q.put(1)
q.put(2)

# q.put(3,block=True,timeout=3) # 默认是阻塞的 当容器中没有位置了就阻塞 直到有人从里面取走元素为止
# block：是否阻塞，默认是True，如果为False就不会阻塞，但是满了会报错
# timeout：阻塞等待的时间，超出就不阻塞
print(q.get())
print(q.get())
print(q.get(block=True,timeout=3))

Extended: Stack

Is a special container that particular access order is last out

Function call stack

Function call stack when calling function

Function call function execution end pop