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From Brian Bockelman <bbock...@cse.unl.edu>
Subject Re: libhdfs process fork problem
Date Tue, 27 Mar 2012 18:49:06 GMT
Hi Tareq,

Sorry - out of ideas, without doing something like "strace"ing the process to verify that
the master never tries to initialize a JVM.

If exec'ing doesn't work, then it is certainly something in the environment.


On Mar 27, 2012, at 10:07 AM, Tareq Aljabban wrote:

> Hi Brian,
> Thanks for your response..
> Actually the master process doesn't even try to access HDFS..
> What's happening is that process Master forks 2 processes A and B.
> A and B are the ones that try to connect to HDFS..
> I tried doing this in a separate application and it worked.. for some reason it doesn't
work in the other application that I'm working on.
> Since I'm not connecting from master then I cannot really apply any of your advices..
do you have other ideas?
> Thanks
> On Fri, Mar 23, 2012 at 7:25 AM, Brian Bockelman <bbockelm@cse.unl.edu> wrote:
> Hi Tareq,
> This is because libhdfs will keep a bit of state data (especially if the master was connected
to HDFS).
> Three suggestions:
> 1) [Likely to work] Fork the children first, then do any HDFS actions in the master.
 Alternately, don't have the master do any HDFS actions; have it fork a child which does them
for it.
> 2) [May work] Try disconnecting the master from HDFS, then forking the children.
> 3) [If 2 doesn't work] Have the master disconnect, then fork the children, then have
the children exec.
> Brian
> On Mar 22, 2012, at 11:38 PM, Tareq Aljabban wrote:
> > Hi,
> > I'm using libhdfs C interface to access HDFS.
> > The application accessing HDFS has a master process that forks many
> > processes, and these processes try to connect to HDFS.
> > Upon connection, one of the processes is exiting as soon as it reaches the
> > hdfsConnect().
> > I tried simulating this behavior by creating a separate application where
> > the master process forks two processes that connect to HDFS and send
> > requests.. this worked without any problem.. so I got confused.. what's
> > really causing the connection problems then?
> > Any insights on this is much appreciated.

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