Python标准模块--concurrent.futures(进程池,线程池)

时间：2022-01-01 21:50:55

python为我们提供的标准模块concurrent.futures里面有ThreadPoolExecutor(线程池)和ProcessPoolExecutor(进程池)两个模块. 在这个模块里他们俩在用法上是一样的.

concurrent.futures官方文档: https://docs.python.org/dev/library/concurrent.futures.html

#1 介绍

concurrent.futures模块提供了高度封装的异步调用接口

ThreadPoolExecutor：线程池，提供异步调用

ProcessPoolExecutor: 进程池，提供异步调用

Both implement the same interface, which is defined 
by the abstract Executor class.

#2 基本方法

#submit(fn, *args, **kwargs)

异步提交任务

#map(func, *iterables, timeout=None, chunksize=1)

取代for循环submit的操作

#shutdown(wait=True)

相当于进程池的pool.close()+pool.join()操作

wait=True，等待池内所有任务执行完毕回收完资源后才继续

wait=False，立即返回，并不会等待池内的任务执行完毕

但不管wait参数为何值，整个程序都会等到所有任务执行完毕

submit和map必须在shutdown之前

#result(timeout=None)

取得结果

#add_done_callback(fn)

回调函数
#介绍

The ProcessPoolExecutor class is an Executor subclass that uses a pool of processes to execute calls asynchronously. ProcessPoolExecutor uses the multiprocessing module, which allows it to side-step the Global Interpreter Lock but also means that only picklable objects can be executed and returned.

class concurrent.futures.ProcessPoolExecutor(max_workers=None, mp_context=None)

An Executor subclass that executes calls asynchronously using a pool of at most max_workers processes. If max_workers is None or not given, it will default to the number of processors on the machine. If max_workers is lower or equal to 0, then a ValueError will be raised.

# 用法示例

from concurrent.futures import ThreadPoolExecutor

import time

def func(n):

    time.sleep(1)

    print(">>>", n)

    return n*n

if __name__ == '__main__':

    t_pool = ThreadPoolExecutor(max_workers=5) # 线程池中最多不要超过cup个数*5

    t_list = []

    for i in range(20):

        res = t_pool.submit(func, i)

        t_list.append(res)

    t_pool.shutdown()   # 等待子线程结束, 再执行父进程 相当于相当于进程池的pool.close()+pool.join()操作

    for resl in t_list:

        print(resl.result()) # 结果是有序的, 这是因为t_list中的元素就是

                            # 有序的,所以循环迭代从结果对象中取出的值也是有序的

ThreadPoolExecutor

#介绍

ThreadPoolExecutor is an Executor subclass that uses a pool of threads to execute calls asynchronously.

class concurrent.futures.ThreadPoolExecutor(max_workers=None, thread_name_prefix='')

An Executor subclass that uses a pool of at most max_workers threads to execute calls asynchronously.

Changed in version 3.5: If max_workers is None or not given, it will default to the number of processors on the machine, multiplied by 5, assuming that ThreadPoolExecutor is often used to overlap I/O instead of CPU work and the number of workers should be higher than the number of workers for ProcessPoolExecutor.

New in version 3.6: The thread_name_prefix argument was added to allow users to control the threading.Thread names for worker threads created by the pool for easier debugging.

#用法

与ThreadPoolExecutor相同, 将ThreadPoolExecutor换成Process就可以了

ProcessPoolExecutor

from concurrent.futures import ThreadPoolExecutor

import time

def func(n):

    time.sleep(1)

    print(">>>", n)

    return n*n

if __name__ == '__main__':

    t_pool = ThreadPoolExecutor(max_workers=5)

    res_g = t_pool.map(func,range(20))# 取代了for + submit 得到的结果是一个生成器对象

    t_pool.shutdown()

    print("主线程")

    for ress in res_g:

        print(ress)

map用法示例

from concurrent.futures import ThreadPoolExecutor,ProcessPoolExecutor

from multiprocessing import Pool

import requests

import json

import os

def get_page(url):

    print('<进程%s> get %s' %(os.getpid(),url))

    respone=requests.get(url)

    if respone.status_code == 200:

        return {'url':url,'text':respone.text}

def parse_page(res):

    res=res.result()

    print('<进程%s> parse %s' %(os.getpid(),res['url']))

    parse_res='url:<%s> size:[%s]\n' %(res['url'],len(res['text']))

    with open('db.txt','a') as f:

        f.write(parse_res)

if __name__ == '__main__':

    urls=[

        'https://www.baidu.com',

        'https://www.python.org',

        'https://www.openstack.org',

        'https://help.github.com/',

        'http://www.sina.com.cn/'

    ]

    # p=Pool(3)

    # for url in urls:

    #     p.apply_async(get_page,args=(url,),callback=pasrse_page)

    # p.close()

    # p.join()

    p=ProcessPoolExecutor(3)

    for url in urls:

        p.submit(get_page,url).add_done_callback(parse_page) #parse_page拿到的是一个future对象obj，需要用obj.result()拿到结果

回调函数

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