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

[Paul Malolepsy (JIRA)]

    [ http://opensource.atlassian.com/projects/hibernate/browse/HHH-2481?page=comments#action_26465 ] 

Paul Malolepsy commented on HHH-2481:
-------------------------------------

Yep, that thread discusses this issue exactly.

I'm afraid the leak is as large as I stated.  The static thread local is created on *each* proxy type.  So if my application has a Customer class and a Order class, each type has their own static thread local, and the last proxy object created of each type on each thread will be leaked.  

RE: fixing the issue differently.  That occurred to me too.  I though you might just be able to call one of the Enhancer.create() methods which let you pass in the callback directly, but I figured there must have been a reason why that wasn't chosen (sounds like I was right) so I decided to respect the original design.   But one little extra call to clear the thread local should be a pretty minimal impact.

> 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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