day31
由于GIL的存在,python中的多线程其实并不是真正的多线程,如果想要充分地使用多核CPU的资源,在python中大部分情况需要使用多进程。Python提供了非常好用的多进程包multiprocessing,只需要定义一个函数,Python会完成其他所有事情。借助这个包,可以轻松完成从单进程到并发执行的转换。
多进程
1 from multiprocessing import Process#进程
2 import time
3 def f(name):
4 time.sleep(1)
5 print('hello', name,time.ctime())
6
7 if __name__ == '__main__':
8 p_list=[]
9 for i in range(3):#和threading,差不多
10 p = Process(target=f, args=('alvin',))
11 p_list.append(p)
12 p.start()
13 for i in p_list:
14 p.join()
15 print('end')
16
17 #延迟一秒后全部输出
延迟1面。输出。
执行结果:
/home/nizhipeng/PycharmProjects/learnPython/venv/bin/python /home/nizhipeng/PycharmProjects/learnPython/week8/多进程.py
hello alvin Mon Nov 5 22:25:45 2018
hello alvin Mon Nov 5 22:25:45 2018
hello alvin Mon Nov 5 22:25:45 2018
end
Process finished with exit code 0
类式调用多线程
1 from multiprocessing import Process
2 import time
3
4 class MyProcess(Process):#继承
5 def __init__(self):
6 super(MyProcess, self).__init__()
7 #self.name = name 可以从新赋值
8
9 def run(self):
10 time.sleep(1)
11 print ('hello', self.name,time.ctime())#hello MyProcess-3 Mon Nov 5 21:20:11 2018
12
13
14 if __name__ == '__main__':
15 p_list=[]
16 for i in range(3):
17 p = MyProcess()
18 p.start()
19 p_list.append(p)
20
21 for p in p_list:
22 p.join()
23
24 print('end')
使用方式和threading多线程一样。
执行结果:
hello MyProcess-1 Mon Nov 5 22:27:51 2018
hello MyProcess-2 Mon Nov 5 22:27:51 2018
hello MyProcess-3 Mon Nov 5 22:27:51 2018
end
Process finished with exit code 0
进程关系
1 from multiprocessing import Process
2 import os
3 import time
4 def info(title):
5 print(title)#传入信息
6 print('module name:', __name__)#main
7 print('parent process:', os.getppid())#父进程号
8 print('process id:', os.getpid())#本进程号
9 #每一个进程都有根进程
10
11 def f(name):
12 info('\033[31;1mfunction f\033[0m')
13 print('hello', name)
14
15 if __name__ == '__main__':
16 info('\033[32;1mmain process line\033[0m')
17 time.sleep(3)
18 p = Process(target=info, args=('bob',))#子进程 ,其父进程是主进程
19 p.start()
20 p.join()
执行结果:
main process line
module name: __main__
parent process: 4319
process id: 1896
bob
module name: __main__
parent process: 1896
process id: 1929
Process finished with exit code 0
从输出结果可以看出,子进程p的父进程号1896是主进程号1896。主进程的父进程号是4319。
每一个进程都有根进程
主进程与子进程通信Pipe
1 from multiprocessing import Process, Pipe
2
3
4 def f(conn):
5 conn.send([42, None, 'hello'])#其中conn,为其父进程的child_conn
6 conn.close()
7
8
9 if __name__ == '__main__':
10 parent_conn, child_conn = Pipe()
11 p = Process(target=f, args=(child_conn,))
12 p.start()
13 print(parent_conn.recv()) # prints "[42, None, 'hello']"#子进程发送,主进程接收
14 p.join()
执行结果:
[42, None, 'hello']
Process finished with exit code 0
manager实现数据共享
1 from multiprocessing import Process, Manager
2 import threading
3 def f(d, l,n):
4 d[n] = '1'#n 为0~1个线程,全赋为1
5 d['2'] = 2
6 d[0.25] = None
7 l.append(n)
8 #print('l:', l)
9
10 if __name__ == '__main__':
11 with Manager() as manager: #manager = manager()
12 d = manager.dict()#字典
13
14 l = manager.list(range(5))#初始值为零到四的列表
15
16 p_list = []
17 for i in range(10):
18 p = Process(target=f, args=(d, l, i))
19 #p = threading.Thread(target=f, args=(d, l, i)) #多线程
20 p.start()
21 p_list.append(p)
22
23 for res in p_list:
24 res.join()
25
26 print(d)
27 print(l)
执行结果:
{0.25: None, 1: '1', 2: '1', 3: '1', '2': 2, 5: '1', 6: '1', 7: '1', 8: '1', 9: '1', 4: '1', 0: '1'}
[0, 1, 2, 3, 4, 1, 0, 6, 2, 3, 7, 4, 8, 9, 5]
Process finished with exit code 0
d字典中,n 0~9,都赋值为1,其余按要求赋值。
列表l中,前五个初始为0~4,后十个值由于是多进程,排列顺序随机。