进程相关问题学习

写在前面，进程同步控制有锁，信号量，事件
进程间通信有 队列和管道

• 信号量
  相当于多个锁

import os
import time
import random
from multiprocessing import Process, Semaphore

def ro(i, sem):
    sem.acquire()
    print('%s in room'.format(i))
    time.sleep(random.randint(5,6))
    print('%s out room'.format(i))
    sem.release()

if __name__ == "__main__":
    sem = Semaphore(4)
    for i in range(20):
        p = Process(target=ro, args=(i, sem))
        p.start()

• 事件
  控制进程的动作

from threading import  Event
e = Event()  # 创建了一个事件
print(e.is_set())    # 查看一个事件的状态
e.set()    # 将事件的状态设置为 True
print(e.is_set())
e.wait()    # 根据 e.is_set() 值决定是否阻塞
e.clear()  # 将事件状态设置为 False
print(e.is_set())

红绿灯问题

import time
import random
from multiprocessing import Process, Event
def cars(e, i):
    if not e.is_set():
        print('car%s在等待'%i)
        e.wait()
    print('%s car通过'%i)

def light(e):
    while True:
        if e.is_set():
            e.clear()
            print('红灯亮了')
        else:
            e.set()
            print('绿灯亮了')
        time.sleep(2)

if __name__ == '__main__':
    e = Event()
    traffic = Process(target=light, args=(e,))
    traffic.start()
    for i in range(20):
        car = Process(target=cars, args=(e, i))
        car.start()
        time.sleep(random.random())

生产者与消费者问题

import time
import random
from multiprocessing import Process, Queue

def consumer(q, name):
     while True:
        food = q.get()
        if food is None:
            print('获取到了一个空')
            break
        print('%s 消费了 %s'%(name, food))
        time.sleep(random.randint(1,3))

def producer(name, food, q):
    for i in range(4):
        time.sleep(random.randint(1,3))
        f = "%s 生产了 %s%s" % (name, food, i)
        print(f)
        q.put(f)
if __name__ == '__main__':
    q = Queue(20) 
    p1 = Process(target=producer, args=('a', 'w', q))
    p2 = Process(target=producer, args=('b', 'w', q))
    c1 = Process(target=consumer, args=(q, 'c1'))
    c2 = Process(target=consumer, args=(q, 'c2'))
    p1.start()
    p2.start()
    c1.start()
    c2.start()
    p1.join()
    p2.join()
    q.put(None)
    q.put(None)

这样太麻烦了，因为有几个生产这就需要放置几个 None。可以使用 JoinableQueue

import time
import random
from multiprocessing import Process
from multiprocessing import JoinableQueue

def consumer(q, name):
    while True:
        food = q.get()
        print('%s 消费了 %s'%(name, food))
        time.sleep(random.randint(1,3))
        q.task_done()

def producer(name, food, q):
    for i in range(4):
        time.sleep(random.randint(1,3))
        f = "%s 生产了 %s%s" % (name, food, i)
        print(f)
        q.put(f)
    q.join()    # 阻塞 直到一个队列中的数据全部被处理完毕

if __name__ == '__main__':
    q = JoinableQueue(20)
    p1 = Process(target=producer, args=('a', 'w', q))
    p2 = Process(target=producer, args=('b', 'w', q))
    c1 = Process(target=consumer, args=(q, 'c1'))
    c2 = Process(target=consumer, args=(q, 'c2'))
    p1.start()
    p2.start()
    c1.daemon = True
    c2.daemon = True
    c1.start()
    c2.start()
    p1.join()
    p2.join()