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https://issues.apache.org/jira/browse/NET-466?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13420805#comment-13420805
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Konrad Garus commented on NET-466:
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I have not inspected the source, just wanted to report/confirm that
{{TelnetInputStream.available()}} seems to be blocking indefinitely. I noticed
this regression after upgrading from 1.4.1 to 3.1.
It's a severe issue for us, blocking update which we direly need for other
areas (FTP client).
> Regression: TelnetInputStream#available() blocks
> ------------------------------------------------
>
> Key: NET-466
> URL: https://issues.apache.org/jira/browse/NET-466
> Project: Commons Net
> Issue Type: Bug
> Components: Telnet
> Affects Versions: 3.1
> Reporter: Martin Oberhuber
> Priority: Critical
> Fix For: 3.1
>
>
> When testing with Commons Net 3.1 for Eclipse
> https://bugs.eclipse.org/bugs/show_bug.cgi?id=194473 , I found that our
> telnet client blocks when the ReaderThread is running and waiting for new
> data. Investigation shows that our code blocks on
> TelnetInputStream#available().
> This regression is due to the code introduced for NET-437 "TelnetInputStream
> doesn't support non-blocking IO when reader thread is not enabled":
> TelnetInputStream#available() now calls super.available() which is declared
> as "synchronized" on BufferedInputStream in JDK 1.6.0_21 at least. But at the
> same time, the telnet ReaderThread has already the Monitor on
> BufferedInputStream and doesn't give it up while sitting in read0().
> This seems to be exactly the situation that the comment before
> TelnetInputStream#close() warns about:
> // Cannot be synchronized. Will cause deadlock if run() is blocked
> // in read because BufferedInputStream read() is synchronized.
> This is a severe issue since it violates the specification and use of
> available().
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