Python多线程（转载）

• Bilibili 蚂蚁学Python UP主说得很好
• 工作中看视频不方便，截取重点部分改为文字版，方便抄作业
• 原地址：https://www.bilibili.com/video/BV1bK411A7tV

多线程

1. 定义一个函数

def my_func(a,b):
    do_something(a,b)

2. 创建线程

import threading

t = threading.Thread(target=my_func, args=(a, b))

3. 启动线程

t.start()

4. 等待结束

t.join()

队列

• queue.Queue是线程安全的

import queue

q = queue.Queue()

# 添加与获取
q.put(time)
item = q.get()

# 查看状态
q.qsize()
q.empty()
q.full()

线程安全（锁）

1. try-finally

import threading

lock = threading.Lock()
lock.acquire()
try:
    # do something
finally:
    lock.release()

2. with

import threading

lock = threading.Lock()
with lock:
    # do something

线程池

1. map函数，结果预入参顺序对应

from concurrent.futures import ThreadPoolExecutor

arg_list = []

with ThreadPoolExecutor() as pool:
    results = pool.map(my_func, arg_list)

    for result in results:
        print(results)

2. submit函数，as_completed顺序可按完成顺序

from concurrent.futures import ThreadPoolExecutor, as_completed

arg_list = []

with ThreadPoolExecutor() as pool:
    futures = [pool.submit(my_func, arg) for arg in arg_list]

    # 按输入顺序
    for future in futures:
        print(future.result())

    # 按完成顺序
    for future in as_completed(futures):
        print(future.result())

Flask中使用线程池

import time
from concurrent.futures import ThreadPoolExecutor
from flask import Flask

app = Flask(__name__)
pool = ThreadPoolExecutor()


def do_1():
    time.sleep(1)
    return 'do_1'


def do_2():
    time.sleep(1)
    return 'do_2'


def do_3():
    time.sleep(1)
    return 'do_3'


@app.route("/")
def index():
    result_1 = pool.submit(do_1)
    result_2 = pool.submit(do_2)
    result_3 = pool.submit(do_3)
    return {
        '1': result_1.result(),
        '2': result_2.result(),
        '3': result_3.result(),
    }


if __name__ == "__main__":
    app.run()

多进程

图片截图自 蚂蚁学Python Bilibili 03:00

Flask使用多进程

import time
from concurrent.futures import ProcessPoolExecutor
from flask import Flask

app = Flask(__name__)


def do_1():
    time.sleep(1)
    return 'do_1'


def do_2():
    time.sleep(1)
    return 'do_2'


def do_3():
    time.sleep(1)
    return 'do_3'


@app.route("/")
def index():
    result_1 = pool.submit(do_1)
    result_2 = pool.submit(do_2)
    result_3 = pool.submit(do_3)
    return {
        '1': result_1.result(),
        '2': result_2.result(),
        '3': result_3.result(),
    }


if __name__ == "__main__":
    pool = ProcessPoolExecutor()
    app.run()

协程：asyncio、await

import asyncio
import aiohttp

loop = asyncio.get_event_loop()


async def get_url(url):
    async with aiohttp.ClientSession() as session:
        async with session.get(url) as resp:
            result = await resp.text()
            print(f"url:{url},{len(result)}")


urls = [f"https://www.cnblogs.com/#p{page}" for page in range(1, 50 + 1)]

tasks = [loop.create_task(get_url(url)) for url in urls]

loop.run_until_complete(asyncio.wait(tasks))

控制asyncio并发数

1. try-finally

import asyncio
sem = asyncio.Semaphore(10)

await sem.acquire()
try:
    # do something
finally:
    sem.release()

2. with

import asyncio
sem = asyncio.Semaphore(10)

async with sem:
    # do something

• 举例

import asyncio
import aiohttp

loop = asyncio.get_event_loop()

# 限制10个并发
semaphore = asyncio.Semaphore(10)


async def get_url(url):
    async with semaphore:
        async with aiohttp.ClientSession() as session:
            async with session.get(url) as resp:
                result = await resp.text()
                print(f"url:{url},{len(result)}")


urls = [f"https://www.cnblogs.com/#p{page}" for page in range(1, 50 + 1)]

tasks = [loop.create_task(get_url(url)) for url in urls]

loop.run_until_complete(asyncio.wait(tasks))