CODEWITHSUNDEEP
pythonpython-2.7exceptionmultiprocessing
CoMartel
CoMartel

Reputation: 3591

Handling Exception in multiprocess

I have 2 processes A and B, communicating through a multiprocessing.Pipe(), and I would like raise an exception in B when A fails. For now I have something like that:

def A_function():
    try:
        a,b=Pipe()
        B=Process(target=B_function,args=(b,))
        B.start()
        while True:
            a.send(data)
            data_recv=a.recv()
    except Exception as e:
        print e
        #  terminate process properly

def B_function(b):
    try:
        while True:
            data_recv=b.recv()
            # do some work on data_recv, but can fail
            b.send(modified_data)
    except Exception as e:
        print e
        raise # not working on the other process `A`

A=Process(target=A_function)
A.start()

If process B fails, there is nothing happening on A. I wonder if there is a pythonic way to transmit the exception to A or if I should send some dummy message through the Pipe, or kill the Pipe to raise an Error in A, but that doesn't seem very clean.

Upvotes: 4

Views: 910

Answers (1)

mguijarr
mguijarr

Reputation: 7930

AFAIK you need to send your own message through the pipe. It seems like you want to send exception from B to A. The code in B for exception handling could be like this:

class RemoteException(object):
    def __init__(self, exc, err_string, tb):
        self.exception = exc
        self.error_string = err_string
        self.tb = tb

try:
    data_recv = b.recv()
except Exception:
    exception, error_string, tb = sys.exc_info()
    b.send(RemoteException(exception, error_string, tb))
    ...

In A:

while True:
    ..
    data_recv = a.recv()
    if isinstance(data_recv, RemoteException):
        raise data_recv.error_string, None, data_recv.tb

Of course both A and B processes should share the same RemoteException class.

Upvotes: 5

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