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https://issues.apache.org/jira/browse/NET-466?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13420833#comment-13420833
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Konrad Garus commented on NET-466:
----------------------------------
The issue disappears as soon as I disable the reader thread.
Here are relevant stacktraces from the lock-up:
{code}"Thread-0" daemon prio=10 tid=0x00007f721c61a000 nid=0x3dea runnable
[0x00007f7218ee7000]
java.lang.Thread.State: RUNNABLE
at java.net.SocketInputStream.socketRead0(Native Method)
at java.net.SocketInputStream.read(SocketInputStream.java:129)
at java.io.BufferedInputStream.read1(BufferedInputStream.java:256)
at java.io.BufferedInputStream.read(BufferedInputStream.java:317)
- locked <0x00000007d70f7510> (a java.io.BufferedInputStream)
at java.io.BufferedInputStream.fill(BufferedInputStream.java:218)
at java.io.BufferedInputStream.read(BufferedInputStream.java:237)
- locked <0x00000007d70fbab0> (a
org.apache.commons.net.telnet.TelnetInputStream)
at
org.apache.commons.net.telnet.TelnetInputStream.__read(TelnetInputStream.java:140)
at
org.apache.commons.net.telnet.TelnetInputStream.run(TelnetInputStream.java:608)
at java.lang.Thread.run(Thread.java:662)
Locked ownable synchronizers:
- None
"main" prio=10 tid=0x00007f721c00d000 nid=0x3dd0 waiting for monitor entry
[0x00007f7223c29000]
java.lang.Thread.State: BLOCKED (on object monitor)
at java.io.BufferedInputStream.available(BufferedInputStream.java:381)
- waiting to lock <0x00000007d70fbab0> (a
org.apache.commons.net.telnet.TelnetInputStream)
at
org.apache.commons.net.telnet.TelnetInputStream.available(TelnetInputStream.java:563)
- locked <0x00000007d70fe320> (a [I)
at java.io.BufferedInputStream.available(BufferedInputStream.java:381)
- locked <0x00000007d7100498> (a java.io.BufferedInputStream)
at com.example.Main.main(Main.java:95)
Locked ownable synchronizers:
- None
{code}
> 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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