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https://issues.apache.org/jira/browse/SPARK-26019?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16692722#comment-16692722
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Liang-Chi Hsieh commented on SPARK-26019:
-----------------------------------------

{{TCPServer}} begins to process requests only after we call its 
{{serve_forever}} method. When the server goes to process a request, it will 
instantiate {{RequestHandlerClass}}:

https://github.com/python/cpython/blob/2.7/Lib/SocketServer.py#L332

As {{RequestHandlerClass}} in {{AccumulatorServer}} is 
{{_UpdateRequestHandler}}, at the moment, {{_UpdateRequestHandler.handle}} is 
called and to access {{auth_token}}.

All of above should be happened after we call {{serve_forever}} in 
{{_start_update_server}}:

{code}
def _start_update_server(auth_token):
    """Start a TCP server to receive accumulator updates in a daemon thread, 
and returns it"""
    server = AccumulatorServer(("localhost", 0), _UpdateRequestHandler, 
auth_token)
    thread = threading.Thread(target=server.serve_forever)
{code}

And I think that we already finish instantiating {{AccumulatorServer}} and 
{{self.auth_token = auth_token}} is run.

> pyspark/accumulators.py: "TypeError: object of type 'NoneType' has no len()" 
> in authenticate_and_accum_updates()
> ----------------------------------------------------------------------------------------------------------------
>
>                 Key: SPARK-26019
>                 URL: https://issues.apache.org/jira/browse/SPARK-26019
>             Project: Spark
>          Issue Type: Bug
>          Components: PySpark
>    Affects Versions: 2.3.2, 2.4.0
>            Reporter: Ruslan Dautkhanov
>            Priority: Major
>
> Started happening after 2.3.1 -> 2.3.2 upgrade.
>  
> {code:python}
> Exception happened during processing of request from ('127.0.0.1', 43418)
> ----------------------------------------
> Traceback (most recent call last):
>   File "/opt/cloudera/parcels/Anaconda/lib/python2.7/SocketServer.py", line 
> 290, in _handle_request_noblock
>     self.process_request(request, client_address)
>   File "/opt/cloudera/parcels/Anaconda/lib/python2.7/SocketServer.py", line 
> 318, in process_request
>     self.finish_request(request, client_address)
>   File "/opt/cloudera/parcels/Anaconda/lib/python2.7/SocketServer.py", line 
> 331, in finish_request
>     self.RequestHandlerClass(request, client_address, self)
>   File "/opt/cloudera/parcels/Anaconda/lib/python2.7/SocketServer.py", line 
> 652, in __init__
>     self.handle()
>   File 
> "/opt/cloudera/parcels/SPARK2-2.3.0.cloudera4-1.cdh5.13.3.p0.611179/lib/spark2/python/lib/pyspark.zip/pyspark/accumulators.py",
>  line 263, in handle
>     poll(authenticate_and_accum_updates)
>   File 
> "/opt/cloudera/parcels/SPARK2-2.3.0.cloudera4-1.cdh5.13.3.p0.611179/lib/spark2/python/lib/pyspark.zip/pyspark/accumulators.py",
>  line 238, in poll
>     if func():
>   File 
> "/opt/cloudera/parcels/SPARK2-2.3.0.cloudera4-1.cdh5.13.3.p0.611179/lib/spark2/python/lib/pyspark.zip/pyspark/accumulators.py",
>  line 251, in authenticate_and_accum_updates
>     received_token = self.rfile.read(len(auth_token))
> TypeError: object of type 'NoneType' has no len()
>  
> {code}
>  
> Error happens here:
> https://github.com/apache/spark/blob/cb90617f894fd51a092710271823ec7d1cd3a668/python/pyspark/accumulators.py#L254
> The PySpark code was just running a simple pipeline of 
> binary_rdd = sc.binaryRecords(full_file_path, record_length).map(lambda .. )
> and then converting it to a dataframe and running a count on it.
> It seems error is flaky - on next rerun it didn't happen.



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