协程和进程-CFANZ编程社区

多进程

fork()

案例

# -*- coding: utf-8 -*-,
# @File : test0.py,
# @Author : lidong,
# @IDEA: PyCharm
# @Time :  2022/4/26 09:52

import os

print('Process (%s) start...' % os.getpid())
# Only works on Unix/Linux/Mac:
pid = os.fork()
print(pid)
if pid == 0:
    print('I am child process (%s) and my parent is %s.' % (os.getpid(), os.getppid()))
else:
    print('I (%s) just created a child process (%s).' % (os.getpid(), pid))

运行结果

Process (48602) start...
48603
I (48602) just created a child process (48603).
0
I am child process (48603) and my parent is 48602.

Process finished with exit code 0

multiprocessing

案例

# -*- coding: utf-8 -*-,
# @File : test0.py,
# @Author : lidong,
# @IDEA: PyCharm
# @Time :  2022/4/26 09:52

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',)) # 创建子进程时，只需要传入一个执行函数和函数的参数，创建一个Process实例
    print('Child process will start.')
    p.start() # 用start()方法启动
    p.join()
    print('Child process end.') # join()方法可以等待子进程结束后再继续往下运行，通常用于进程间的同步。

运行结果

Parent process 48737.
Child process will start.
Run child process test (48739)...
Child process end.

Process finished with exit code 0

Pool

案例


# -*- coding: utf-8 -*-,
# @File : test0.py,
# @Author : lidong,
# @IDEA: PyCharm
# @Time :  2022/4/26 09:52

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()#对Pool对象调用join()方法会等待所有子进程执行完毕，调用join()之前必须先调用close()，调用close()之后就不能继续添加新的Process了。
    print('All subprocesses done.')

运行结果 (每次运行结果不一致)

Parent process 48788.
Waiting for all subprocesses done...
Run task 0 (48791)...
Run task 1 (48790)...
Run task 2 (48793)...
Run task 3 (48792)...
Task 3 runs 0.20 seconds.
Run task 4 (48792)...
Task 4 runs 0.14 seconds.
Task 2 runs 0.56 seconds.
Task 0 runs 1.12 seconds.
Task 1 runs 1.15 seconds.
All subprocesses done.

Process finished with exit code 0

进程间通信

案例

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()

运行结果

Process to write: 49151
Put A to queue...
Process to read: 49152
Get A from queue.
Put B to queue...
Get B from queue.
Put C to queue...
Get C from queue.

多线程

_thread和threading

案例

# -*- coding: utf-8 -*-,
# @File : test0.py,
# @Author : lidong,
# @IDEA: PyCharm
# @Time :  2022/4/26 09:52

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) # current_thread()函数，它永远返回当前线程的实例
t = threading.Thread(target=loop, name='LoopThread') # 启动一个线程就是把一个函数传入并创建Thread实例
t.start() # 调用start()开始执行
t.join() 
print('thread %s ended.' % threading.current_thread().name)

运行结果

thread MainThread is running...
thread LoopThread is running...
thread LoopThread >>> 1
thread LoopThread >>> 2
thread LoopThread >>> 3
thread LoopThread >>> 4
thread LoopThread >>> 5
thread LoopThread ended.
thread MainThread ended.

Process finished with exit code 0

Lock

案例

# -*- coding: utf-8 -*-,
# @File : test0.py,
# @Author : lidong,
# @IDEA: PyCharm
# @Time :  2022/4/26 09:52

import  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(2000000):
        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)

运行结果

-8（不唯一）

Process finished with exit code 0

我们定义了一个共享变量balance，初始值为0，
并且启动两个线程，先存后取，理论上结果应该为0，
但是，由于线程的调度是由操作系统决定的，当t1、
t2交替执行时，只要循环次数足够多，balance的
结果就不一定是0了。
初始值 balance = 0

t1: x1 = balance + 5  # x1 = 0 + 5 = 5

t2: x2 = balance + 8  # x2 = 0 + 8 = 8
t2: balance = x2      # balance = 8

t1: balance = x1      # balance = 5
t1: x1 = balance - 5  # x1 = 5 - 5 = 0
t1: balance = x1      # balance = 0

t2: x2 = balance - 8  # x2 = 0 - 8 = -8
t2: balance = x2      # balance = -8

结果 balance = -8

案例

# -*- coding: utf-8 -*-,
# @File : test0.py,
# @Author : lidong,
# @IDEA: PyCharm
# @Time :  2022/4/26 09:52

import threading
lock = threading.Lock()
# 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(2000000):
        lock.acquire() # 先获取锁
        try:
            change_it(n)
        finally:
            lock.release()# 改完了一定要释放锁:


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)

运行结果

0

Process finished with exit code 0

协程和进程

多进程

fork()

multiprocessing

Pool

进程间通信

多线程

_thread和threading

Lock

小结