Pool - Python多进程管理

在Python中多进程管理使用Pool,可以设定最大进程数n，一次执行n个任务，当有一个进程完成后会有新的进程被添加进Pool。

示例代码：

import multiprocessing
import os, time, random

def Lee():
    print "Run task Lee - %s" % (os.getpid())  # os.getpid()获取当前的进程的ID
    start=time.time()
    time.sleep(random.random()*10)  # random.random()随机生成0-1之间的小数
    end=time.time()
    print 'Task Lee, runs %0.2f seconds.' %(end - start)

def Marlon():
    print "Run task Marlon - %s" % (os.getpid())
    start = time.time()
    time.sleep(random.random()*40)
    end = time.time()
    print 'Task Marlon runs %0.2f seconds.' % (end - start)

def Allen():
    print "Run task Allen - %s" % (os.getpid())
    start = time.time()
    time.sleep(random.random()*30)
    end = time.time()
    print 'Task Allen runs %0.2f seconds.' % (end - start)

def Frank():
    print "Run task Frank - %s" % (os.getpid())
    start = time.time()
    time.sleep(random.random()*20)
    end = time.time()
    print 'Task Frank runs %0.2f seconds.' % (end - start)

if __name__ == '__main__':
    function_list = [Lee, Marlon, Allen, Frank]
    print "parent process %s" % (os.getpid())
    pool = multiprocessing.Pool(2)
    for func in function_list:
        pool.apply_async(func)  # Pool执行函数，apply执行函数,当有一个进程执行完毕后，会添加一个新的进程到pool中
    print 'Waiting for all subprocesses done...'
    pool.close()
    pool.join()  # 调用join之前，一定要先调用close() 函数，否则会出错, close()执行后不会有新的进程加入到pool,join函数等待素有子进程结束
    print 'All subprocesses done.'