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From Roman Shapovalov <shapova...@graphics.cs.msu.su>
Subject readNext semantic and failure after cleanup
Date Mon, 30 Sep 2013 12:54:51 GMT
Hello all,

I am developing a toy master-slave application for the Python
streaming interface. There are two issues.

1. What is the semantics of the readNext command?

If I run 3 tasks -- one of them is master who does not read input, --
slaves take turn to read records, but each of them reads only each
third example, e.g. slave#1 reads records 3,6,9, while slave#2 reads
2,5,8. So 1/3 of records are skipped, as if the master task would read
them.

So, what is the exact semantics? Is there any best practice to make
each example read by some task (but not the master).


2. After the code is executed (and the output is written), the job
fails. All the task logs contain the following text:

13/09/30 16:32:09 ERROR protocol.UplinkReader: java.lang.NullPointerException
    at org.apache.hama.pipes.protocol.UplinkReader.run(UplinkReader.java:127)

The exception is raised even if I don't use pipes at all. Since it
shows up after cleanup, it is not critical for the program, but it may
indicate some misuse by me or bugs in the Hama code.

Please look at that issue. My code is attached.

Roman

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