python并發(fā)和異步編程實例

更新時間：2018年11月15日 08:38:29 作者：風(fēng)起云永

這篇文章主要為大家詳細介紹了python并發(fā)和異步編程實例，具有一定的參考價值，感興趣的小伙伴們可以參考一下

關(guān)于并發(fā)、并行、同步阻塞、異步非阻塞、線程、進程、協(xié)程等這些概念，單純通過文字恐怕很難有比較深刻的理解，本文就通過代碼一步步實現(xiàn)這些并發(fā)和異步編程，并進行比較。解釋器方面本文選擇python3，畢竟python3才是python的未來，并且python3用原生的庫實現(xiàn)協(xié)程已經(jīng)非常方便了。

1、準備階段

下面為所有測試代碼所需要的包

#! python3
# coding:utf-8

import socket
from concurrent import futures
from selectors import DefaultSelector,EVENT_WRITE,EVENT_READ
import asyncio
import aiohttp
import time
from time import ctime

在進行不同實現(xiàn)方式的比較時，實現(xiàn)場景就是在進行爬蟲開發(fā)的時候通過向?qū)Ψ骄W(wǎng)站發(fā)起一系列的http請求訪問，統(tǒng)計耗時來判斷實現(xiàn)方式的優(yōu)劣，具體地，通過建立通信套接字，訪問新浪主頁，返回源碼，作為一次請求。先實現(xiàn)一個裝飾器用來統(tǒng)計函數(shù)的執(zhí)行時間：

def tsfunc(func):
  def wrappedFunc(*args,**kargs):
    start = time.clock()
    action = func(*args,**kargs)
    time_delta = time.clock() - start
    print ('[{0}] {1}() called, time delta: {2}'.format(ctime(),func.__name__,time_delta))
    return action
  return wrappedFunc

輸出的格式為：當(dāng)前時間，調(diào)用的函數(shù)，函數(shù)的執(zhí)行時間。

2、阻塞/非阻塞和同步/異步

這兩對概念不是很好區(qū)分，從定義上理解：

阻塞：在進行socket通信過程中，一個線程發(fā)起請求，如果當(dāng)前請求沒有返回結(jié)果，則進入sleep狀態(tài)，期間線程掛起不能做其他操作，直到有返回結(jié)果，或者超時(如果設(shè)置超時的話)。
非阻塞：與阻塞相似，只不過在等待請求結(jié)果時，線程并不掛起而是進行其他操作，即在不能立刻得到結(jié)果之前，該函數(shù)不會阻掛起當(dāng)前線程，而會立刻返回。
同步：同步和阻塞比較相似，但是二者并不是同一個概念，同步是指完成事件的邏輯，是指一件事完成之后，再完成第二件事，以此類推…
異步：異步和非阻塞比較類似，異步的概念和同步相對。當(dāng)一個異步過程調(diào)用發(fā)出后，調(diào)用者不能立刻得到結(jié)果。實際處理這個調(diào)用的部件在完成后，通過狀態(tài)、通知和回調(diào)來通知調(diào)用者，實現(xiàn)異步的方式通俗講就是“等會再告訴你”。

1）阻塞方式

回到代碼上，首先實現(xiàn)阻塞方式的請求函數(shù)：

def blocking_way():
  sock = socket.socket()
  sock.connect(('www.sina.com',80))
  request = 'GET / HTTP/1.0\r\nHOST:www.sina.com\r\n\r\n'
  sock.send(request.encode('ascii'))
  response = b''
  chunk = sock.recv(4096)
  while chunk:
    response += chunk
    chunk = sock.recv(4096)
  return response

測試線程、多進程和多線程

# 阻塞無并發(fā)
@tsfunc
def sync_way():
  res = []
  for i in range(10):
    res.append(blocking_way())
  return len(res)
@tsfunc
# 阻塞、多進程
def process_way():
  worker = 10
  with futures.ProcessPoolExecutor(worker) as executor:
    futs = {executor.submit(blocking_way) for i in range(10)}
  return len([fut.result() for fut in futs])
# 阻塞、多線程
@tsfunc
def thread_way():
  worker = 10
  with futures.ThreadPoolExecutor(worker) as executor:
    futs = {executor.submit(blocking_way) for i in range(10)}
  return len([fut.result() for fut in futs])

運行結(jié)果：

[Wed Dec 13 16:52:25 2017] sync_way() called, time delta: 0.06371647809425328
[Wed Dec 13 16:52:28 2017] process_way() called, time delta: 2.31437644946734
[Wed Dec 13 16:52:28 2017] thread_way() called, time delta: 0.010172946070299727

可見與非并發(fā)的方式相比，啟動10個進程完成10次請求訪問耗費的時間最長，進程確實需要很大的系統(tǒng)開銷，相比多線程則效果好得多，啟動10個線程并發(fā)請求，比順序請求速度快了6倍左右。

2）非阻塞方式

實現(xiàn)非阻塞的請求代碼，與阻塞方式的區(qū)別在于等待請求時并不掛起而是直接返回，為了確保能正確讀取消息，最原始的方式就是循環(huán)讀取，知道讀取完成為跳出循環(huán)，代碼如下：

def nonblocking_way():
  sock = socket.socket(socket.AF_INET,socket.SOCK_STREAM)
  sock.setblocking(False)
  try:
    sock.connect(('www.sina.com', 80))
  except BlockingIOError:
    pass
  request = 'GET / HTTP/1.0\r\nHost: www.sina.com\r\n\r\n'
  data = request.encode('ascii')
  while True:
    try:
      sock.send(data)
      break
    except OSError:
      pass

  response = b''
  while True:
    try:
      chunk = sock.recv(4096)
      while chunk:
        response += chunk
        chunk = sock.recv(4096)
      break
    except OSError:
      pass

  return response

測試單線程異步非阻塞方式：

@tsfunc
def async_way():
  res = []
  for i in range(10):
    res.append(nonblocking_way())
  return len(res)

測試結(jié)果與單線程同步阻塞方式相比：

[Wed Dec 13 17:18:30 2017] sync_way() called, time delta: 0.07342884475822574
[Wed Dec 13 17:18:30 2017] async_way() called, time delta: 0.06509009095694886

非阻塞方式起到了一定的效果，但是并不明顯，原因肯定是讀取消息的時候雖然不是在線程掛起的時候而是在循環(huán)讀取消息的時候浪費了時間，如果大部分時間讀浪費了并沒有發(fā)揮異步編程的威力，解決的辦法就是后面要說的【事件驅(qū)動】

3、回調(diào)、生成器和協(xié)程

a、回調(diào)

class Crawler():
  def __init__(self,url):
    self.url = url
    self.sock = None
    self.response = b''

  def fetch(self):
    self.sock = socket.socket()
    self.sock.setblocking(False)
    try:
      self.sock.connect(('www.sina.com',80))
    except BlockingIOError:
      pass
    selector.register(self.sock.fileno(),EVENT_WRITE,self.connected)

  def connected(self,key,mask):
    selector.unregister(key.fd)
    get = 'GET {0} HTTP/1.0\r\nHost:www.sina.com\r\n\r\n'.format(self.url)
    self.sock.send(get.encode('ascii'))
    selector.register(key.fd,EVENT_READ,self.read_response)

  def read_response(self,key,mask):
    global stopped
    while True:
      try:
        chunk = self.sock.recv(4096)
        if chunk:
          self.response += chunk
          chunk = self.sock.recv(4096)
        else:
          selector.unregister(key.fd)
          urls_todo.remove(self.url)
          if not urls_todo:
            stopped = True
        break
      except:
        pass

def loop():
  while not stopped:
    events = selector.select()
    for event_key,event_mask in events:
      callback = event_key.data
      callback(event_key,event_mask)
 @tsfunc
def callback_way():
  for url in urls_todo:
    crawler = Crawler(url)
    crawler.fetch()
  loop1()

這是通過傳統(tǒng)回調(diào)方式實現(xiàn)的異步編程，結(jié)果如下：

[Tue Mar 27 17:52:49 2018] callback_way() called, time delta: 0.054735804048789374

b、生成器

class Crawler2:
  def __init__(self, url):
    self.url = url
    self.response = b''

  def fetch(self):
    global stopped
    sock = socket.socket()
    yield from connect(sock, ('www.sina.com', 80))
    get = 'GET {0} HTTP/1.0\r\nHost: www.sina.com\r\n\r\n'.format(self.url)
    sock.send(get.encode('ascii'))
    self.response = yield from read_all(sock)
    urls_todo.remove(self.url)
    if not urls_todo:
      stopped = True

class Task:
  def __init__(self, coro):
    self.coro = coro
    f = Future1()
    f.set_result(None)
    self.step(f)

  def step(self, future):
    try:
      # send會進入到coro執(zhí)行, 即fetch, 直到下次yield
      # next_future 為yield返回的對象
      next_future = self.coro.send(future.result)
    except StopIteration:
      return
    next_future.add_done_callback(self.step)

def loop1():
  while not stopped:
    events = selector.select()
    for event_key,event_mask in events:
      callback = event_key.data
      callback()

運行結(jié)果如下：

[Tue Mar 27 17:54:27 2018] generate_way() called, time delta: 0.2914336347673473

c、協(xié)程

def nonblocking_way():
  sock = socket.socket(socket.AF_INET,socket.SOCK_STREAM)
  sock.setblocking(False)
  try:
    sock.connect(('www.sina.com', 80))
  except BlockingIOError:
    pass
  request = 'GET / HTTP/1.0\r\nHost: www.sina.com\r\n\r\n'
  data = request.encode('ascii')
  while True:
    try:
      sock.send(data)
      break
    except OSError:
      pass

  response = b''
  while True:
    try:
      chunk = sock.recv(4096)
      while chunk:
        response += chunk
        chunk = sock.recv(4096)
      break
    except OSError:
      pass

  return response
@tsfunc
def asyncio_way():
    tasks = [fetch(host+url) for url in urls_todo]
    loop.run_until_complete(asyncio.gather(*tasks))
    return (len(tasks))

運行結(jié)果：

[Tue Mar 27 17:56:17 2018] asyncio_way() called, time delta: 0.43688060698484166

到此終于把并發(fā)和異步編程實例代碼測試完，下邊貼出全部代碼，共讀者自行測試，在任務(wù)量加大時，相信結(jié)果會大不一樣。

#! python3
# coding:utf-8

import socket
from concurrent import futures
from selectors import DefaultSelector,EVENT_WRITE,EVENT_READ
import asyncio
import aiohttp
import time
from time import ctime

def tsfunc(func):
  def wrappedFunc(*args,**kargs):
    start = time.clock()
    action = func(*args,**kargs)
    time_delta = time.clock() - start
    print ('[{0}] {1}() called, time delta: {2}'.format(ctime(),func.__name__,time_delta))
    return action
  return wrappedFunc

def blocking_way():
  sock = socket.socket()
  sock.connect(('www.sina.com',80))
  request = 'GET / HTTP/1.0\r\nHOST:www.sina.com\r\n\r\n'
  sock.send(request.encode('ascii'))
  response = b''
  chunk = sock.recv(4096)
  while chunk:
    response += chunk
    chunk = sock.recv(4096)
  return response

def nonblocking_way():
  sock = socket.socket(socket.AF_INET,socket.SOCK_STREAM)
  sock.setblocking(False)
  try:
    sock.connect(('www.sina.com', 80))
  except BlockingIOError:
    pass
  request = 'GET / HTTP/1.0\r\nHost: www.sina.com\r\n\r\n'
  data = request.encode('ascii')
  while True:
    try:
      sock.send(data)
      break
    except OSError:
      pass

  response = b''
  while True:
    try:
      chunk = sock.recv(4096)
      while chunk:
        response += chunk
        chunk = sock.recv(4096)
      break
    except OSError:
      pass

  return response


selector = DefaultSelector()
stopped = False
urls_todo = ['/','/1','/2','/3','/4','/5','/6','/7','/8','/9']


class Crawler():
  def __init__(self,url):
    self.url = url
    self.sock = None
    self.response = b''

  def fetch(self):
    self.sock = socket.socket()
    self.sock.setblocking(False)
    try:
      self.sock.connect(('www.sina.com',80))
    except BlockingIOError:
      pass
    selector.register(self.sock.fileno(),EVENT_WRITE,self.connected)

  def connected(self,key,mask):
    selector.unregister(key.fd)
    get = 'GET {0} HTTP/1.0\r\nHost:www.sina.com\r\n\r\n'.format(self.url)
    self.sock.send(get.encode('ascii'))
    selector.register(key.fd,EVENT_READ,self.read_response)

  def read_response(self,key,mask):
    global stopped
    while True:
      try:
        chunk = self.sock.recv(4096)
        if chunk:
          self.response += chunk
          chunk = self.sock.recv(4096)
        else:
          selector.unregister(key.fd)
          urls_todo.remove(self.url)
          if not urls_todo:
            stopped = True
        break
      except:
        pass

def loop():
  while not stopped:
    events = selector.select()
    for event_key,event_mask in events:
      callback = event_key.data
      callback(event_key,event_mask)


# 基于生成器的協(xié)程
class Future:
  def __init__(self):
    self.result = None
    self._callbacks = []

  def add_done_callback(self,fn):
    self._callbacks.append(fn)

  def set_result(self,result):
    self.result = result
    for fn in self._callbacks:
      fn(self)

class Crawler1():
  def __init__(self,url):
    self.url = url
    self.response = b''

  def fetch(self):
    sock = socket.socket()
    sock.setblocking(False)
    try:
      sock.connect(('www.sina.com',80))
    except BlockingIOError:
      pass

    f = Future()
    def on_connected():
      f.set_result(None)

    selector.register(sock.fileno(),EVENT_WRITE,on_connected)
    yield f
    selector.unregister(sock.fileno())
    get = 'GET {0} HTTP/1.0\r\nHost: www.sina.com\r\n\r\n'.format(self.url)
    sock.send(get.encode('ascii'))

    global stopped
    while True:
      f = Future()
      def on_readable():
        f.set_result(sock.recv(4096))
      selector.register(sock.fileno(),EVENT_READ,on_readable)
      chunk = yield f
      selector.unregister(sock.fileno())
      if chunk:
        self.response += chunk
      else:
        urls_todo.remove(self.url)
        if not urls_todo:
          stopped = True
        break


# yield from 改進的生成器協(xié)程
class Future1:
  def __init__(self):
    self.result = None
    self._callbacks = []

  def add_done_callback(self,fn):
    self._callbacks.append(fn)

  def set_result(self,result):
    self.result = result
    for fn in self._callbacks:
      fn(self)

  def __iter__(self):
    yield self
    return self.result

def connect(sock, address):
  f = Future1()
  sock.setblocking(False)
  try:
    sock.connect(address)
  except BlockingIOError:
    pass

  def on_connected():
    f.set_result(None)

  selector.register(sock.fileno(), EVENT_WRITE, on_connected)
  yield from f
  selector.unregister(sock.fileno())

def read(sock):
  f = Future1()

  def on_readable():
    f.set_result(sock.recv(4096))

  selector.register(sock.fileno(), EVENT_READ, on_readable)
  chunk = yield from f
  selector.unregister(sock.fileno())
  return chunk

def read_all(sock):
  response = []
  chunk = yield from read(sock)
  while chunk:
    response.append(chunk)
    chunk = yield from read(sock)
  return b''.join(response)

class Crawler2:
  def __init__(self, url):
    self.url = url
    self.response = b''

  def fetch(self):
    global stopped
    sock = socket.socket()
    yield from connect(sock, ('www.sina.com', 80))
    get = 'GET {0} HTTP/1.0\r\nHost: www.sina.com\r\n\r\n'.format(self.url)
    sock.send(get.encode('ascii'))
    self.response = yield from read_all(sock)
    urls_todo.remove(self.url)
    if not urls_todo:
      stopped = True


class Task:
  def __init__(self, coro):
    self.coro = coro
    f = Future1()
    f.set_result(None)
    self.step(f)

  def step(self, future):
    try:
      # send會進入到coro執(zhí)行, 即fetch, 直到下次yield
      # next_future 為yield返回的對象
      next_future = self.coro.send(future.result)
    except StopIteration:
      return
    next_future.add_done_callback(self.step)

def loop1():
  while not stopped:
    events = selector.select()
    for event_key,event_mask in events:
      callback = event_key.data
      callback()


# asyncio 協(xié)程
host = 'http://www.sina.com'
loop = asyncio.get_event_loop()

async def fetch(url):
  async with aiohttp.ClientSession(loop=loop) as session:
    async with session.get(url) as response:
      response = await response.read()
      return response

@tsfunc
def asyncio_way():
    tasks = [fetch(host+url) for url in urls_todo]
    loop.run_until_complete(asyncio.gather(*tasks))
    return (len(tasks))

@tsfunc
def sync_way():
  res = []
  for i in range(10):
    res.append(blocking_way())
  return len(res)

@tsfunc
def process_way():
  worker = 10
  with futures.ProcessPoolExecutor(worker) as executor:
    futs = {executor.submit(blocking_way) for i in range(10)}
  return len([fut.result() for fut in futs])

@tsfunc
def thread_way():
  worker = 10
  with futures.ThreadPoolExecutor(worker) as executor:
    futs = {executor.submit(blocking_way) for i in range(10)}
  return len([fut.result() for fut in futs])

@tsfunc
def async_way():
  res = []
  for i in range(10):
    res.append(nonblocking_way())
  return len(res)

@tsfunc
def callback_way():
  for url in urls_todo:
    crawler = Crawler(url)
    crawler.fetch()
  loop1()

@tsfunc
def generate_way():
  for url in urls_todo:
    crawler = Crawler2(url)
    Task(crawler.fetch())
  loop1()

if __name__ == '__main__':

  #sync_way()
  #process_way()
  #thread_way()
  #async_way()
  #callback_way()
  #generate_way()
  asyncio_way()

以上就是本文的全部內(nèi)容，希望對大家的學(xué)習(xí)有所幫助，也希望大家多多支持腳本之家。

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