[hibernate-issues] [Hibernate-JIRA] Commented: (HHH-2481) Big memory leak in the use of CGLIB

[Scott Marlow (JIRA)]

    [ http://opensource.atlassian.com/projects/hibernate/browse/HHH-2481?page=comments#action_26463 ] 

Scott Marlow commented on HHH-2481:
-----------------------------------

My next step is to evaluate whether we could fix the root issue differently (or work around it), that being HHH-1293.  In the original code, we passed the instance in directly which didn't always work on some platforms (especially Linux).   At the very least, we should clear the ThreadLocalStorage reference before returning as your patch does.  

In your example above, is the potential of the leak really that high?  I wouldn't expect 15,000 objects leaked.  Correct me if I'm wrong, but I would expect one TLS slot per thread to hold a reference.  If you have 100 threads, that is a max of 100 objects leaked.  Unless a collection is stored in each TLS slot and then the potential is higher.  Either way, we should fix the leak.

http://forum.hibernate.org/viewtopic.php?t=947902 seems to discuss this issue as well.

> Big memory leak in the use of CGLIB
> -----------------------------------
>
>          Key: HHH-2481
>          URL: http://opensource.atlassian.com/projects/hibernate/browse/HHH-2481
>      Project: Hibernate3
>         Type: Bug

>   Components: core
>     Versions: 3.2.2
>  Environment: Hibernate 3.2.2
> MySQL 5.1
>     Reporter: Paul Malolepsy
>     Assignee: Scott Marlow
>     Priority: Critical
>  Attachments: fix.diff
>
> Original Estimate: 5 minutes
>         Remaining: 5 minutes
>
> The way CGLIBLazyInitializer is creating proxies is resulting in a potentially massive memory leak.
> In CGLIBLazyInitializer.getProxy() just before the proxy is instantiated, a call is made to Enhancer.registerCallbacks() passing in the instance of CGLIBLazyInitializer that will manage the proxy.  This variable is stored in a static ThreadLocal on the CGLIB created persistentClass so that any subsequent objects instantiated will get this callback class.  
> The problem is that once this ThreadLocal is set, it is never cleared, so it will stay around (together with the object it's managing, and whatever object graph it may be connected to) until the next time a proxy is created for that type on that thread.  
> For our application we have about 150 different proxy types, and our app can have over 100 threads.  This results in potentially 15,000 proxy objects and their graphs stuck in memory.
> The fix for this is simple.  Just make another call the Enhancer.registerCallbacks() with a null callback arg, right after the proxy class is instantiated:
> Enhancer.registerCallbacks(factory, null);

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