python 多进程 —— multiprocessing.Process

由于Python是跨平台的，自然也应该提供一个跨平台的多进程支持。

multiprocessing模块就是跨平台版本的多进程模块。

multiprocessing模块提供了一个Process类来代表一个进程对象。

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

start()方法启动，这样创建进程比fork()还要简单。

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。

使用 join()

# -*- coding:utf-8 -*-
from multiprocessing import Process
import os
import time


def run_proc(name):
    time.sleep(10)
    print('Run child process %s (%s)...' % (name, os.getpid()))


def hello_world():
    # time.sleep(5)
    time.sleep(20)
    print('hello world!')
    print('Run child process (%s)...' % (os.getpid()))


if __name__ == '__main__':
    print ('Parent process %s.' % os.getpid())
    p1 = Process(target=run_proc, args=('test',))
    p2 = Process(target=hello_world)
    print 'Process will start.'
    p1.start()
    p2.start()
    p1.join()
    print('Process end.')

输出：

Parent process 11860.
Process will start.
Run child process test (11232)...
Process end.
hello world!
Run child process (2288)...

Process finished with exit code 0

---

子进程的开始时间

# -*- coding:utf-8 -*-
from multiprocessing import Process
import os
import time


def run_proc(name):
    print(time.time())

    time.sleep(10)
    print('Run child process %s (%s)...' % (name, os.getpid()))


def hello_world():
    print(time.time())

    # time.sleep(5)
    time.sleep(20)
    print('hello world!')
    print('Run child process (%s)...' % (os.getpid()))


if __name__ == '__main__':
    print ('Parent process %s.' % os.getpid())
    p1 = Process(target=run_proc, args=('test',))
    p2 = Process(target=hello_world)
    print 'Process will start.'
    p1.start()
    p2.start()
    p1.join()
    print('Process end.')

输出：

Parent process 7220.
Process will start.
1496374096.56
1496374096.56
Run child process test (2196)...
Process end.
hello world!
Run child process (832)...

Process finished with exit code 0

可以认为 子进程 p1 与 子进程 p2 同时开始

---

去掉 join(),使用 map

# -*- coding:utf-8 -*-
from multiprocessing import Process
import os
import time


def run_proc(name):
    print(time.time())

    time.sleep(10)
    print('Run child process %s (%s)...' % (name, os.getpid()))


def hello_world():
    print(time.time())

    # time.sleep(5)
    time.sleep(20)
    print('hello world!')
    print('Run child process (%s)...' % (os.getpid()))


if __name__ == '__main__':
    print ('Parent process %s.' % os.getpid())
    p1 = Process(target=run_proc, args=('test',))
    p2 = Process(target=hello_world)
    print 'Process will start.'
    # p1.start()
    # p2.start()
    # p1.join()
    p_list = (p1, p2)
    map(Process.start, p_list)
    print('Process end.')

输出：

Parent process 8580.
Process will start.
Process end.
1496374397.24
1496374397.24
Run child process test (7148)...
hello world!
Run child process (8348)...

Process finished with exit code 0

---