python multiprocessing apply_async only uses one process

发布时间:April 20, 2016 // 分类:开发笔记,python,生活琐事 // No Comments

某天写了一个多进程的东西。发现无法准确获得返回结果

import os
from multiprocessing import Pool

results = []
def testFunc(files):
    for file in files:
        print "Working in Process #%d" % (os.getpid())
        #This is just an illustration of some logic. This is not what I'm actually doing.
        for line in file:
            if 'dog' in line:
                results.append(line)

if __name__=="__main__":
    p = Pool(processes=2)
    files = ['/path/to/file1.txt', '/path/to/file2.txt']
    results = p.apply_async(testFunc, args = (files,))
    results2 = results.get()
  • apply_async farms out one task to the pool. You would need to call apply_async many times to exercise more processors.
  • Don't allow both processes to try to write to the same list, results. Since the pool workers are separate processes, the two won't be writing to the same list. One way to work around this is to use an ouput Queue. You could set it up yourself, or use apply_async's callback to setup the Queue for you. apply_async will call the callback once the function completes.
  • You could use map_async instead of apply_async, but then you'd get a list of lists, which you'd then have to flatten.

然后更改为

import os
import multiprocessing as mp

results = []   

def testFunc(file):
    result = []
    print "Working in Process #%d" % (os.getpid())
    # This is just an illustration of some logic. This is not what I'm
    # actually doing.
    with open(file, 'r') as f:
        for line in f:
            if 'dog' in line:
                result.append(line)
    return result


def collect_results(result):
    results.extend(result)

if __name__ == "__main__":
    p = mp.Pool(processes=2)
    files = ['/path/to/file1.txt', '/path/to/file2.txt']
    for f in files:
        p.apply_async(testFunc, args=(f, ), callback=collect_results)
    p.close()
    p.join()
    print(results)

再有

import os
from multiprocessing import Pool

results = []
def testFunc(file):
    message =  ("Working in Process #%d" % (os.getpid()))
    #This is just an illustration of some logic. This is not what I'm actually doing.
    for line in file:
        if 'dog' in line:
            results.append(line)
    return message

if __name__=="__main__":
    print("saddsf")
    p = Pool(processes=2)
    files = ['/path/to/file1.txt', '/path/to/file2.txt']
    results = p.map_async(testFunc, files)
    print(results.get())

感觉第二种方式靠谱一些

标签:apply_async, map_async

添加新评论 »

分类
最新文章
最近回复
  • 轨迹: niubility!
  • 没穿底裤: 好办法..
  • emma: 任务计划那有点小问题,调用后Activation.exe不是当前活动窗口,造成回车下一步下一步...
  • 没穿底裤: hook execve函数
  • tuhao lam: 大佬,还有持续跟进Linux命令执行记录这块吗?通过内核拦截exec系统调用的方式,目前有没有...