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From "Gary D. Gregory (JIRA)" <>
Subject [jira] [Commented] (NET-466) Regression: TelnetInputStream#available() blocks
Date Wed, 30 May 2012 02:15:23 GMT


Gary D. Gregory commented on NET-466:

Are you saying that all methods in {{BufferedInputStream}} marked with {{synchronized}} should
also be marked as such in {{TelnetInputStream}}?

This in TelnetClient is confusing:

protected void _connectAction_() throws IOException
        TelnetInputStream tmp = new TelnetInputStream(_input_, this, readerThread);
        // __input CANNOT refer to the TelnetInputStream.  We run into
        // blocking problems when some classes use TelnetInputStream, so
        // we wrap it with a BufferedInputStream which we know is safe.
        // This blocking behavior requires further investigation, but right
        // now it looks like classes like InputStreamReader are not implemented
        // in a safe manner.
        __input = new BufferedInputStream(tmp);
        __output = new TelnetOutputStream(this);

{{TelnetInputStream}} subclasses {{BufferedInputStream}} and this method wraps the {{TelnetInputStream}}
in a {{BufferedInputStream}}. Is that what is intended here? If so, it needs better docs!
> Regression: TelnetInputStream#available() blocks
> ------------------------------------------------
>                 Key: NET-466
>                 URL:
>             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
, 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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