Thanks Nicky - really appreciate the input and help!! Will look at
adding the dead lock detection code
cheers,
Rob
http://rajdavies.blogspot.com/
On Oct 18, 2007, at 3:07 PM, Nicky Sandhu wrote:
Hi Rob,
It was not my intention to question your skill, rather it was to
point that
synchronizations lead to deadlocks (potentially) and they are too
difficult
to predict and code review. So I was proposing adding a deadlock
detector
like the one referenced below to optional activemq code.
I see a lot of threads on hung producer/consumer/broker issues and
if such
a deadlock detector could be run either on demand or periodically
it would
help the team in pinpointing deadlock issues. Ofcourse not all hung
issues
would be deadlocks but this can't hurt.
Very gently,
Nicky
rajdavies wrote:
Thanks Nicky!
will apply patches asap - we're usually pretty good at avoiding
deadlocks :(
cheers,
Rob
http://rajdavies.blogspot.com/
On Oct 17, 2007, at 10:40 PM, Nicky Sandhu wrote:
Hi folks,
I got hit by another deadlock condition. Thats two different ones
on two
consecutive days :(
In ActiveMQ I see a lot of blocks of code using synchronized
access, nothing
wrong with that but this increases the potential for deadlocks as
evidenced
by the last two problems I have hit within the span of a couple of
days
(https://issues.apache.org/activemq/browse/AMQ-1467,
https://issues.apache.org/activemq/browse/AMQ-1468)
This may be just my luck but I think it points to concurrency 101
lessons
(http://undergraduate.csse.uwa.edu.au/units/CITS3213/lectures2/
lect4.pdf)
some which are a.) Lock on the appropriate object 2.) don't hold
locks for
longer than absolutely necessary 3.) avoid nested locks like the
plague. 4.)
Establish locking order for nested locks etc.
Thoughts?
Nicky
BTW. JConsole has a cool detect deadlock feature in jdk6 which
makes this
exercise quick (once you stumble across the deadlock that is >:)) +
this
article (http://www.javaspecialists.eu/archive/Issue130.html) has
code that
you can run periodically to dump them when they happen... something
to be
included in perhaps a debug version to help root all these out ?
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