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From "Martin Oberhuber (JIRA)" <>
Subject [jira] [Created] (NET-466) Regression: TelnetInputStream#available() blocks
Date Thu, 24 May 2012 13:40:55 GMT
Martin Oberhuber created NET-466:

             Summary: Regression: TelnetInputStream#available() blocks
                 Key: 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
, 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
    // 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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