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Hadoop, mail # user - hadoop FileSystem.close()


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Re: hadoop FileSystem.close()
Edward Capriolo 2012-07-24, 14:46
In all my experience you let FileSystem instances close themselves.

On Tue, Jul 24, 2012 at 10:34 AM, Koert Kuipers <[EMAIL PROTECTED]> wrote:
> Since FileSystem is a Closeable i would expect code using it to be like
> this:
>
> FileSystem fs = path.getFileSystem(conf);
> try {
>     // do something with fs, such as read from the path
> } finally {
>     fs.close()
> }
>
> However i have repeatedly gotten into trouble with this approach. In one
> situation it turned out that when i closed a FileSystem other operations
> that were using their own FileSystems (pointing to the same real-world HDFS
> filesystem) also saw their FileSystems closed, leading to very confusing
> read and write errors. This led me to believe that FileSystem should never
> be closed since it seemed to act like some sort of Singleton. However now
> was just looking at some code (Hoop server, to be precise) and noticed that
> FileSystems were indeed closed, but they were always threadlocal. Is this
> the right approach?
>
> And if FileSystem is threadlocal, is this safe (assuming fs1 and fs2 could
> point to the same real-world filesystem)?
>
> FileSystem fs1 = path.getFileSystem(conf);
> try {
>     FileSystem fs2 = path.getFileSystem(conf);
>     try {
>     // do something with fs2, such as read from the path
>     } finally {
>       fs2.close()
>     }
>     // do something with fs1, such as read from the path (note, fs2 is
> closed here, and i wouldn't be surprised if fs1 by now is also closed given
> my experience)
> } finally {
>   fs1.close()
> }