Channel writes being made without OP_WRITE selector ready
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Key: DIRMINA-362
URL: https://issues.apache.org/jira/browse/DIRMINA-362
Project: MINA
Issue Type: Bug
Components: Core
Affects Versions: 1.0.2, 1.0.1, 1.0.0
Environment: Windows 2000, JDK 1.4+, JBoss 4.0.4GA
Reporter: Michael Kearns
We've been experiencing 100%CPU Kernel locks when utilising the Mitosis
directory replication within Apache Directory. The error manifests itself
within the SocketIoProcessor class, with an instantly returning selector, yet
no selected keys. It would only happen when Directory replication (within our
JBoss environment) was enabled, against a non-existant client, and suggests a
concurrency issue.
Although there are several JVM bugs registered in this area, none seemed to be
the problem at hand, although troubleshooting was somewhat difficult in that
the problem is not reproducible 'at will'.
After much testing, I found (amongst other issues) that the
doFlush(SocketSessionImpl session) method would attempt to write data without
checking the appropriate selector flags. This would initially result in a
NotYetConnected exception, and then subsequent spinning of the selector.
I can't say with 100% certainty that adding a check in this location fixes the
problem, but after 72 hours of uptime in my last test, I have yet to experience
the problem, whereas it would usually occur within the first few hours of
running.
The snippet below demonstrates the change, with the 'if' test on the key
writability being th only change, wrapped around the existing write section.
if (key.isWritable())
{
int writtenBytes = ch.write( buf.buf() );
if( writtenBytes > 0 )
{
session.increaseWrittenBytes( writtenBytes );
}
}
So far as I can tell, this code hasn't changed from 1.0.0 upwards, and so the
patch would need to be apllied to the 1.0.3 and 2.0.x streams.
I hope this is of help, and the fix can be applied to 1.0.3 as it's quite a
critical problem from our usage.
Regards,
Michael.
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