9.7 池

为什么要有池：

• 预先的开启固定个数的进程数，当任务来临的时候，直接提交给已经开好的进程

• 这些已经开好的进程直接去执行程序

• 节省了进程、线程开启、关闭、切换的时间

• 并且减轻了操作系统的调度负担

9.7.1 进程池

import os import timeimport randomfrom concurrent.futures import ProcessPoolExecutor​df func():    print('start',os.gitpid())    time.sleep(random.random())    print('edf',os.getpid())

if __name__ == '__main__':    p = ProcessPollExcutor(5)    for i in range(10):        p.submit()    p.shutdown() #关闭池之后就不能继续提交任务，并且会阻塞，直到已经提交的任务完成    print('main',os.getpid())

任务参数+返回值

from concurrent.futures import ProcessPoolExecutordef func(i,name):    print('start',os.getpid())    time.sleep(random.randint(1,3))    print('end', os.getpid())    return '%s * %s'%(i,os.getpid())​if __name__ =='__main__':    p = ProcessPoolExcutor(5)    ret_l = []    for i in range(10):        ret = p.submit(func,i,'liujia')        ret_l.append(ret)    for ret in ret_l:        print('ret---->',ret.result())#ret.result()同步阻塞    print('main',os.getpid())

9.7.2 线程池

from concurrent.futures import ThreadPoolExecutordef func(i):    print('start', os.getpid())    time.sleep(random.randint(1,3))    print('end', os.getpid())    return '%s * %s'%(i,os.getpid())tp = ThreadPoolExecutor(20)ret_l = []for i in range(10):    ret = tp.submit(func,i)    ret_l.append(ret)tp.shutdown()print('main')for ret in ret_l:    print('------>',ret.result())

利用map简化

from concurrent.futures import ThreadPoolExecutordef func(i):    print('start', os.getpid())    time.sleep(random.randint(1,3))    print('end', os.getpid())    return '%s * %s'%(i,os.getpid())tp = ThreadPoolExecutor(20)ret = tp.map(func,range(20))  #0-20都去执行func函数for i in ret:    #生成每一个任务的返回值    print(i)ret_l = []for i in range(10):    ret = tp.submit(func,i)    ret_l.append(ret)tp.shutdown()print('main')

回调函数

import requestsfrom concurrent.cutures import ThreadPoolExecutordef get_page(url):    res = requests.get(url)    return {'url':url,'content':res.txt}​def paeserpage(ret): #ret其实就是get_page函数的返回值    dic = ret.result()    print(dic['url'])

tp = ThreadPoolExecutor(5):url_list = ['http://www.baidu.com',   # 3    'http://www.cnblogs.com', # 1    'http://www.douban.com',  # 1    'http://www.tencent.com',    'http://www.cnblogs.com/Eva-J/articles/8306047.html',    'http://www.cnblogs.com/Eva-J/articles/7206498.html',]​ret = []  #中转站for url in url_list:    ret = tp.submit(get_page,url)    ret_l.append(ret)    ret.add_done_callback(parserpage) #哪一个线程先回来就先执行