Python多进程编程详解

序. multiprocessing

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。multiprocessing支持子进程、通信和共享数据、执行不同形式的同步,提供了Process、Queue、Pipe、Lock等组件。

1. Process

创建进程的类:Process([group [, target [, name [, args [, kwargs]]]]]),target表示调用对象,args表示调用对象的位置参数元组。kwargs表示调用对象的字典。name为别名。group实质上不使用。

方法:is_alive()、join([timeout])、run()、start()、terminate()。其中,Process以start()启动某个进程。

属性:authkey、daemon(要通过start()设置)、exitcode(进程在运行时为None、如果为–N,表示被信号N结束)、name、pid。其中daemon是父进程终止后自动终止,且自己不能产生新进程,必须在start()之前设置。

例1.1:创建函数并将其作为单个进程

import multiprocessing
import time

def worker(interval):
    n = 5
    while n > 0:
        print("The time is {0}".format(time.ctime()))
        time.sleep(interval)
        n -= 1

if __name__ == "__main__":
    p = multiprocessing.Process(target = worker, args = (3,))
    p.start()
    print ("p.pid:", p.pid)
    print ("p.name:", p.name)
    print ("p.is_alive:", p.is_alive())

运行结果:

p.pid: 2322
p.name: Process-1
p.is_alive: True
The time is Sun May  5 07:36:18 2019
The time is Sun May  5 07:36:21 2019
The time is Sun May  5 07:36:24 2019
The time is Sun May  5 07:36:27 2019
The time is Sun May  5 07:36:30 2019
[Finished in 15.2s]

Python多进程编程详解

例1.2:创建函数并将其作为多个进程

import multiprocessing
import time

def worker_1(interval):
    print ("worker_1")
    time.sleep(interval)
    print ("end worker_1")

def worker_2(interval):
    print ("worker_2")
    time.sleep(interval)
    print ("end worker_2")

def worker_3(interval):
    print ("worker_3")
    time.sleep(interval)
    print ("end worker_3")

if __name__ == "__main__":
    p1 = multiprocessing.Process(target = worker_1, args = (2,))
    p2 = multiprocessing.Process(target = worker_2, args = (3,))
    p3 = multiprocessing.Process(target = worker_3, args = (4,))

    p1.start()
    p2.start()
    p3.start()

    print("The number of CPU is:" + str(multiprocessing.cpu_count()))
    for p in multiprocessing.active_children():
        print("child   p.name:" + p.name + "\tp.id" + str(p.pid))
    print ("END!!!!!!!!!!!!!!!!!")

运行结果如下:

worker_2
worker_1
worker_3
The number of CPU is:1
child  p.name:Process-3 p.id2783
child  p.name:Process-1 p.id2781
child  p.name:Process-2 p.id2782
END!!!!!!!!!!!!!!!!!
end worker_1
end worker_2
end worker_3
[Finished in 4.1s]

Python多进程编程详解

例1.3:将进程定义为类

import multiprocessing
import time

class ClockProcess(multiprocessing.Process):
    def __init__(self, interval):
        multiprocessing.Process.__init__(self)
        self.interval = interval

    def run(self):
        n = 5
        while n > 0:
            print("the time is {0}".format(time.ctime()))
            time.sleep(self.interval)
            n -= 1

if __name__ == '__main__':
    p = ClockProcess(3)
    p.start()

注:进程p调用start()时,自动调用run()

结果如下:

the time is Sun May  5 07:45:05 2019
the time is Sun May  5 07:45:08 2019
the time is Sun May  5 07:45:11 2019
the time is Sun May  5 07:45:14 2019
the time is Sun May  5 07:45:17 2019
[Finished in 15.1s]

Python多进程编程详解

例1.4:daemon程序对比结果

#1.4-1 不加daemon属性

import multiprocessing
import time

def worker(interval):
    print("work start:{0}".format(time.ctime()));
    time.sleep(interval)
    print("work end:{0}".format(time.ctime()));

if __name__ == "__main__":
    p = multiprocessing.Process(target = worker, args = (3,))
    p.start()
    print ("end!")

结果如下:

end!
work start:Sun May  5 07:46:54 2019
work end:Sun May  5 07:46:57 2019
[Finished in 3.1s]

Python多进程编程详解

#1.4-2 加上daemon属性

import multiprocessing
import time

def worker(interval):
    print("work start:{0}".format(time.ctime()));
    time.sleep(interval)
    print("work end:{0}".format(time.ctime()));

if __name__ == "__main__":
    p = multiprocessing.Process(target = worker, args = (3,))
    p.daemon = True
    p.start()
    print ("end!")

结果如下:

end!
[Finished in 0.1s]

Python多进程编程详解

注:因子进程设置了daemon属性,主进程结束,它们就随着结束了。

#1.4-3 设置daemon执行完结束的方法

import multiprocessing
import time

def worker(interval):
    print("work start:{0}".format(time.ctime()));
    time.sleep(interval)
    print("work end:{0}".format(time.ctime()));

if __name__ == "__main__":
    p = multiprocessing.Process(target = worker, args = (3,))
    p.daemon = True
    p.start()
    p.join()
    print ("end!")

结果如下:

work start:Sun May  5 07:49:59 2019
work end:Sun May  5 07:50:02 2019
end!
[Finished in 3.1s]

Python多进程编程详解

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