如何将异常从一个进程传递到另一个进程？

问题描述

如果停止函数中的运行状态为‘STOPPED’，我想在Upload函数中引发异常。这似乎行不通。我正在使用管道传递异常。出什么问题了？

def upload(instances, u1):
    for instance in instance:
        try:
            u1.recv()
            #do_something
        except:
            #do_something_else
            continue         

def stop(instances, s1):
    for instance in instances:
        RunningStatus = instance[4]
        if RunningStatus.lower() == 'stopped'.lower():
            s1.send(Exception) # I want to raise exception in upload function 
                               # from here

if __name__ == '__main__':
    s1, u1 = multiprocessing.Pipe()
    s = multiprocessing.Process(target = stop, args = (instances, s1,))
    u = multiprocessing.Process(target = upload, args = (instances, u1))
    s.start()
    u.start()
    u.join()

---

解决方案

下面是一个如何将异常对象从一个进程发送到另一个进程的示例。我还尝试发送完整的异常信息(由sys.exc_info返回)，但理所当然地失败了。用户始终可以将回溯信息格式化为字符串并将其发送(请参阅回溯模块)。

在Ubuntu 14.04 Python 2.7、3.4(Ubuntu提供)和3.5(Continuum)上测试。

from __future__ import print_function

import sys
import multiprocessing
import time

def upload(u1):
    i=0
    try:
        while True:
            print('>upload>',i)
            i+=1
            if u1.poll():
                # tvt = u1.recv()
                # raise tvt[0], tvt[1], tvt[2] # Python 2.7
                e = u1.recv()
                raise e
            time.sleep(0.1)
    except Exception as e:
        print('Exception caught:',e)
        print('exiting')

def stop(s1):
    try:
        while True:
            for j in range(100,110):
                time.sleep(0.1)
                if 105==j:
                    raise RuntimeError("oh dear at j={}".format(j))
    except Exception as e:
        # tvt = sys.exc_info()
        # s1.send(tvt) # doesn't work; tracebacks are not pickle'able
        s1.send(e)

if __name__ == '__main__':
    s1, u1 = multiprocessing.Pipe()
    s = multiprocessing.Process(target = stop, args = (s1,))
    u = multiprocessing.Process(target = upload, args = (u1,))
    s.start()
    u.start()
    u.join()

输出：

>upload> 0
>upload> 1
>upload> 2
>upload> 3
>upload> 4
>upload> 5
>upload> 6
Exception caught: oh dear at j=105
exiting