python 多进程、多线程与协程初探

近来接手一个项目，里面大量用到多线程、协程，因此顺便重新学习了。本文中大多代码是直接引用廖雪峰博客上的，为的只是以后方便找出模块的用法样例，特此声明。

名词解释

进程 process
线程 thread
协程 coroutine

关系与背景知识

一个进程里至少有一个线程，即一个进程里可以有多个线程，由于python中的线程有GIL(global interpreter lock)锁，因此python中一个进程里的多线程不是并发执行的。

但是可以用多进程的方法进行分布式编程，也可以用协程（异步IO）提高CPU利用率，最好的搭配是多进程+多协程的方法。

当然，CPython牛逼的，可以改写GIL锁，使得python的多线程做到可以并发。

多进程的模块及其使用

os.fork()与os.getpid(),os.getppid()


# Only works on Unix/Linux/Mac:
pid = os.fork() # create process

if pid == 0:
    # when pid == 0, it's parent pid
    print(os.getpid(), os.getppid())

else:
    # when pid != 0, it's child pid
    print(os.getpid(), pid)

multiprocessing.Process()

from multiprocessing import Process
import os

# 子进程要执行的代码
def run_proc(name):
    print('Run child process %s (%s)...' % (name, os.getpid()))

if __name__=='__main__':
    print('Parent process %s.' % os.getpid())
    p = Process(target=run_proc, args=('test',))
    print('Child process will start.')
    p.start()
    p.join()
    print('Child process end.')

pool

from multiprocessing import Pool
import os, time, random

def long_time_task(name):
    print('Run task %s (%s)...' % (name, os.getpid()))
    start = time.time()
    time.sleep(random.random() * 3)
    end = time.time()
    print('Task %s runs %0.2f seconds.' % (name, (end - start)))

if __name__=='__main__':
    print('Parent process %s.' % os.getpid())
    p = Pool(4)
    for i in range(5):
        p.apply_async(long_time_task, args=(i,))
    print('Waiting for all subprocesses done...')
    p.close()
    p.join()
    print('All subprocesses done.')

subprocess: call() and communicate() and Popen()

import subprocess

print('$ nslookup www.python.org')
r = subprocess.call(['nslookup', 'www.python.org'])
print('Exit code:', r)

print('$ nslookup')
p = subprocess.Popen(['nslookup'], stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
output, err = p.communicate(b'set q=mx\npython.org\nexit\n')
print(output.decode('utf-8'))
print('Exit code:', p.returncode)

进程间通信: queue.Queue

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

# 写数据进程执行的代码:
def write(q):
    print('Process to write: %s' % os.getpid())
    for value in ['A', 'B', 'C']:
        print('Put %s to queue...' % value)
        q.put(value)
        time.sleep(random.random())

# 读数据进程执行的代码:
def read(q):
    print('Process to read: %s' % os.getpid())
    while True:
        value = q.get(True)
        print('Get %s from queue.' % value)

if __name__=='__main__':
    # 父进程创建Queue，并传给各个子进程：
    q = Queue()
    pw = Process(target=write, args=(q,))
    pr = Process(target=read, args=(q,))
    # 启动子进程pw，写入:
    pw.start()
    # 启动子进程pr，读取:
    pr.start()
    # 等待pw结束:
    pw.join()
    # pr进程里是死循环，无法等待其结束，只能强行终止:
    pr.terminate()

多线程的模块及其使用

threading, notice the join()

import time, threading

# 新线程执行的代码:
def loop():
    print('thread %s is running...' % threading.current_thread().name)
    n = 0
    while n < 5:
        n = n + 1
        print('thread %s >>> %s' % (threading.current_thread().name, n))
        time.sleep(1)
    print('thread %s ended.' % threading.current_thread().name)

print('thread %s is running...' % threading.current_thread().name)
t = threading.Thread(target=loop, name='LoopThread')
t.start()
t.join()
print('thread %s ended.' % threading.current_thread().name)

whitout lock

import time, threading

# 假定这是你的银行存款:
balance = 0

def change_it(n):
    # 先存后取，结果应该为0:
    global balance
    balance = balance + n
    balance = balance - n

def run_thread(n):
    for i in range(100000):
        change_it(n)

t1 = threading.Thread(target=run_thread, args=(5,))
t2 = threading.Thread(target=run_thread, args=(8,))
t1.start()
t2.start()
t1.join()
t2.join()
print(balance)

with lock

balance = 0
lock = threading.Lock()

def run_thread(n):
    for i in range(100000):
        # 先要获取锁:
        lock.acquire()
        try:
            # 放心地改吧:
            change_it(n)
        finally:
            # 改完了一定要释放锁:
            lock.release()

multiprocessing.cpu_count()

import threading, multiprocessing

def loop():
    x = 0
    while True:
        x = x ^ 1

for i in range(multiprocessing.cpu_count()):
    t = threading.Thread(target=loop)
    t.start()

ThreadLocal

import threading

# 创建全局ThreadLocal对象:
local_school = threading.local()

def process_student():
    # 获取当前线程关联的student:
    std = local_school.student
    print('Hello, %s (in %s)' % (std, threading.current_thread().name))

def process_thread(name):
    # 绑定ThreadLocal的student:
    local_school.student = name
    process_student()

t1 = threading.Thread(target= process_thread, args=('Alice',), name='Thread-A')
t2 = threading.Thread(target= process_thread, args=('Bob',), name='Thread-B')
t1.start()
t2.start()
t1.join()
t2.join()

分布式进程: master

# task_master.py must be light.

import random, time, queue
from multiprocessing.managers import BaseManager

# 发送任务的队列:
task_queue = queue.Queue()
# 接收结果的队列:
result_queue = queue.Queue()

# 从BaseManager继承的QueueManager:
class QueueManager(BaseManager):
    pass

# 把两个Queue都注册到网络上, callable参数关联了Queue对象:
QueueManager.register('get_task_queue', callable=lambda: task_queue)
QueueManager.register('get_result_queue', callable=lambda: result_queue)
# 绑定端口5000, 设置验证码'abc':
manager = QueueManager(address=('', 5000), authkey=b'abc')
# 启动Queue:
manager.start()
# 获得通过网络访问的Queue对象:
task = manager.get_task_queue()
result = manager.get_result_queue()
# 放几个任务进去:
for i in range(10):
    n = random.randint(0, 10000)
    print('Put task %d...' % n)
    task.put(n)
# 从result队列读取结果:
print('Try get results...')
for i in range(10):
    r = result.get(timeout=10)
    print('Result: %s' % r)
# 关闭:
manager.shutdown()
print('master exit.')

分布式进程: worker

# task_worker.py do the heavy thing

import time, sys, queue
from multiprocessing.managers import BaseManager

# 创建类似的QueueManager:
class QueueManager(BaseManager):
    pass

# 由于这个QueueManager只从网络上获取Queue，所以注册时只提供名字:
QueueManager.register('get_task_queue')
QueueManager.register('get_result_queue')

# 连接到服务器，也就是运行task_master.py的机器:
server_addr = '127.0.0.1'
print('Connect to server %s...' % server_addr)
# 端口和验证码注意保持与task_master.py设置的完全一致:
m = QueueManager(address=(server_addr, 5000), authkey=b'abc')
# 从网络连接:
m.connect()
# 获取Queue的对象:
task = m.get_task_queue()
result = m.get_result_queue()
# 从task队列取任务,并把结果写入result队列:
for i in range(10):
    try:
        n = task.get(timeout=1)
        print('run task %d * %d...' % (n, n))
        r = '%d * %d = %d' % (n, n, n*n)
        time.sleep(1)
        result.put(r)
    except Queue.Empty:
        print('task queue is empty.')
# 处理结束:
print('worker exit.')

协程的模块及其使用

yield: can receive data(when generator.send()) and return data.

def consumer():
    r = ''
    while True:
        n = yield r
        if not n:
            return
        print('[CONSUMER] Consuming %s...' % n)
        r = '200 OK'

def produce(c):
    c.send(None)
    n = 0
    while n < 5:
        n = n + 1
        print('[PRODUCER] Producing %s...' % n)
        r = c.send(n)
        print('[PRODUCER] Consumer return: %s' % r)
    c.close()

c = consumer()
produce(c)

asyncio: sleep(), get_event_loop() [which is the funcs be decorate by coroutine]

import asyncio

@asyncio.coroutine
def hello():
    print("Hello world!")
    # 异步调用asyncio.sleep(1):
    r = yield from asyncio.sleep(1)
    print("Hello again!")

# 获取EventLoop:
loop = asyncio.get_event_loop()
# 执行coroutine
loop.run_until_complete(hello())
loop.close()

asyncio: yield from [which means await this step and to do other thing]

import threading
import asyncio

@asyncio.coroutine
def hello():
    print('Hello world! (%s)' % threading.currentThread())
    yield from asyncio.sleep(1)
    print('Hello again! (%s)' % threading.currentThread())

loop = asyncio.get_event_loop()
tasks = [hello(), hello()]
loop.run_until_complete(asyncio.wait(tasks))
loop.close() # remember to close.

asyncio.wait([%this is a list%]), run_until_complete()

import asyncio

@asyncio.coroutine
def wget(host):
    print('wget %s...' % host)
    connect = asyncio.open_connection(host, 80)
    reader, writer = yield from connect
    header = 'GET / HTTP/1.0\r\nHost: %s\r\n\r\n' % host
    writer.write(header.encode('utf-8'))
    yield from writer.drain()
    while True:
        line = yield from reader.readline()
        if line == b'\r\n':
            break
        print('%s header > %s' % (host, line.decode('utf-8').rstrip()))
    # Ignore the body, close the socket
    writer.close()

loop = asyncio.get_event_loop()
tasks = [wget(host) for host in ['www.sina.com.cn', 'www.sohu.com', 'www.163.com']]
loop.run_until_complete(asyncio.wait(tasks))
loop.close()

async, await

@asyncio.coroutine
def hello():
    print("Hello world!")
    r = yield from asyncio.sleep(1)
    print("Hello again!")

# asyncio.coroutine -> async def 
# yield from -> await

async def hello():
    print("Hello world!")
    r = await asyncio.sleep(1)
    print("Hello again!")

# this grammer start from python 3.5

aiohttp? why not use flask?

import asyncio

from aiohttp import web

async def index(request):
    await asyncio.sleep(0.5)
    return web.Response(body=b'<h1>Index</h1>')

async def hello(request):
    await asyncio.sleep(0.5)
    text = '<h1>hello, %s!</h1>' % request.match_info['name']
    return web.Response(body=text.encode('utf-8'))

async def init(loop):
    app = web.Application(loop=loop)
    app.router.add_route('GET', '/', index)
    app.router.add_route('GET', '/hello/{name}', hello)
    srv = await loop.create_server(app.make_handler(), '127.0.0.1', 8000)
    print('Server started at http://127.0.0.1:8000...')
    return srv

loop = asyncio.get_event_loop()
loop.run_until_complete(init(loop))
loop.run_forever()

参考链接

廖雪峰-多进程

廖雪峰-异步IO