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<HTML>
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<TITLE>Package edu.rit.pj.io</TITLE>
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Package edu.rit.pj.io contains classes
for parallel file input and output
in Parallel Java (PJ) programs.
<P>
To run a PJ program
on a cluster parallel computer,
the user logs into the cluster's <B>frontend processor</B>
and runs the PJ program with the <TT>java</TT> command.
That process is the <B>job frontend process.</B>
The job frontend process contacts
some number of <B>backend processors</B> in the cluster
and causes each backend processor
to run a <B>job backend process.</B>
It is the job backend processes,
running on the backend processors,
that execute the actual PJ program.
The job frontend process performs a supervisory role
but does not execute the actual PJ program.
For further information,
see package <A HREF="../cluster/package-summary.html">edu.rit.pj.cluster</A>.
<P>
This architecture poses a problem if the PJ program needs to do file I/O.
The job backend processes are typically running
in a special PJ account,
not in the user's account.
Also, the job backend processes' working directories
are temporary directories created for the job,
not the user's working directory.
Therefore, the job backend processes
are not able to access files in the user's account
using the normal Java file I/O classes.
<P>
Package edu.rit.pj.io to the rescue!
An instance of class <A HREF="StreamFile.html">StreamFile</A>
refers to a file in the user's account
relative to the user's working directory
where the job frontend process is running.
When a job backend process opens an input stream or output stream
on a <A HREF="StreamFile.html">StreamFile</A>
and reads or writes the stream,
the job backend process forwards all the stream operations
to the job frontend process,
which in turn performs the actual file I/O.
<P>
In summary,
to access a file in the user's account in the frontend processor,
use class <A HREF="StreamFile.html">StreamFile</A>.
To access a file in the PJ account in the backend processor,
use the regular Java I/O classes.
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