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From "L (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (VFS-640) Synchronized AbstractOriginatingFileProvider.getFileSystem is too broad
Date Thu, 24 Aug 2017 08:08:00 GMT

    [ https://issues.apache.org/jira/browse/VFS-640?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16139746#comment-16139746
] 

L commented on VFS-640:
-----------------------

Well, if it is called recursively for layered filesystems, it is *different* provider, I guess.


And as for the original case: it was an SFTP provider where the server had a lot of files
(like more than 2000) in the root directory for the user. 

> Synchronized AbstractOriginatingFileProvider.getFileSystem is too broad
> -----------------------------------------------------------------------
>
>                 Key: VFS-640
>                 URL: https://issues.apache.org/jira/browse/VFS-640
>             Project: Commons VFS
>          Issue Type: Bug
>    Affects Versions: 2.0, 2.1
>            Reporter: L
>         Attachments: ParallelConnTest.java, patch_VFS640.diff
>
>
> Currently (rev. 1802455) this method looks like this:
> {code:java}
>     protected synchronized FileSystem getFileSystem(final FileName rootName, final FileSystemOptions
fileSystemOptions)
>         throws FileSystemException
>     {
>         FileSystem fs = findFileSystem(rootName, fileSystemOptions);
>         if (fs == null)
>         {
>             // Need to create the file system, and cache it
>             fs = doCreateFileSystem(rootName, fileSystemOptions);
>             addFileSystem(rootName, fs);
>         }
>         return fs;
>     }
> {code}
> Given that there is a single instance of a provider per scheme, a very slow server that
is being accessed first time will block *all* other threads trying to access some other resources
via the same provider.
> We have a server that takes sometimes 20-30 seconds in doCreateFileSystem. We do not
mind the thread trying to access this method taking that long, but because of that "synchronized"
we end up having multiple threads accessing unrelated servers for the same scheme blocked.
> PS. Actually, it is not only AbstractOriginatingFileProvider. The same "provider-scoped"
lock is present in AbstractLayeredFileProvider, TemporaryFileProvider, and UrlFileProvider



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