Martin Oberhuber created NET-466:
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Summary: 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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