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From Andrus Adamchik <>
Subject Re: Large number of EventManager threads causing OutOfMemoryException
Date Fri, 30 Apr 2010 01:47:49 GMT
Hi Vic,

There are two possible explanations - EventManager leaking threads  
(seems rather unlikely) or you are starting multiple Cayenne stacks  
(or create multiple EventManagers as a side effect of some other  

A few ways to detect this from a thread dump:

1. Check the names of the cayenne-edt- threads. Specifically check the  
last part of the name - the number after the last dash. E.g. in  
"cayenne-edt-16165743-0", this number is "0". If this number is non- 
repeating and increments indefinitely, that may indicate a leak,  
however if this number is something rather low (e.g. between 0 and 4)  
and repeats many times, this means that multiple EventManagers are  
started somehow.

2. Check the address of the lock of the even thread pool:

> org.apache.cayenne.event.EventManager 
> $
>        - locked &lt;0x96d28c40&gt; (a
> java.util.Collections$SynchronizedList)

(it is "0x96d28c40" in the example above). If it is the same for all  
threads, then it is a leak. If it is different for most threads, then  
you have multiple EM's.


On Apr 30, 2010, at 1:07 AM, Victor Leung wrote:

> Hi all,
> We are using Cayenne 3.0RC3. Our application has a web tier and a  
> business /
> data access tier (both deployed on Glassfish v2.1.1). Communication  
> between
> the two tiers is through the use of Cayenne Web Service.
> We have been encountering OutOfMemoryException after a couple of  
> days of
> routine usage. Heap dumps show a large number of daemon threads  
> associated
> with EventManager. As an example, there are some 13,000 entries in  
> the heap
> dump similar to this:
>    &quot;cayenne-edt-16165743-0&quot; daemon prio=10 tid=0x576d3800
> nid=0x5b2a in Object.wait() [0x847ad000]
>       java.lang.Thread.State: TIMED_WAITING (on object monitor)
>        at java.lang.Object.wait(Native Method)
>        at
> org.apache.cayenne.event.EventManager 
> $
>        - locked &lt;0x96d28c40&gt; (a
> java.util.Collections$SynchronizedList)
> There are no evidence of any deadlocked threads.
> We have since turned on monitoring on the JVM. It appears that the  
> number of
> daemon threads stays more-or-less constant whilst we are just  
> reading from
> the DB, but will creep up slowly over time whenever we do any sort  
> of DB
> updates.
> Any hints as to how we can get around this problem would be much
> appreciated!
> Thanks in advance,
> Vic

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