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From "Alexander Klimetschek (JIRA)" <>
Subject [jira] Updated: (COCOON-2070) Releasing of pooled beans might skip recycle() call on aggregated beans (leading to: "Generator already set"-style exceptions)
Date Tue, 29 May 2007 14:55:16 GMT


Alexander Klimetschek updated COCOON-2070:

    Attachment: poolable-recycle-bug.patch

This patch solves the problem by not using RequestContextHolder.currentRequestAttributes()
but by calling RequestContextHolder.getRequestAttributes() and checking for a null value.
This way the attribute SCOPE_REQUEST is only removed when the attributes are available and
no exception is thrown by Spring.

Secondly I removed the two try/catch statements where this exception was swallowed and added
a re-throw as RuntimeException (because we are inside a

Please, never swallow exceptions! It makes debugging really, really hard :-(

> Releasing of pooled beans might skip recycle() call on aggregated beans (leading to:
"Generator already set"-style exceptions)
> ------------------------------------------------------------------------------------------------------------------------------
>                 Key: COCOON-2070
>                 URL:
>             Project: Cocoon
>          Issue Type: Bug
>          Components: - Components: Sitemap
>    Affects Versions: 2.2-dev (Current SVN)
>            Reporter: Alexander Klimetschek
>            Priority: Blocker
>             Fix For: 2.2-dev (Current SVN)
>         Attachments: poolable-recycle-bug.patch
> There is a serious bug in o.a.c.core.container.spring.avalon.PoolableProxyHandler (and
PoolableFactoryBean) that can lead to exceptions like "Cannot set reader. Generator already
set". This is because the pipeline impl bean is reused from the pool, but was never recycle()d.
The recycle() call is skipped in cases when an exception is thrown by Spring inside PoolableProxyHandler.invoke("putBackIntoAvalonPool")
- this exception is simply swalled by both and PoolableFactoryBean.putIntoPool().
> The typical behaviour is that the first call to the pipeline works, but because the components
are put back into the pool unrecycled, the next call will fail. If there is lots of activity,
you might get a fresh component from the pool and it might work again, so the error seems
quite random.
> The problematic exception happens when RequestContextHolder.currentRequestAttributes()
is called when the attributes for the request are null: IllegalStateException("No thread-bound
request found:....."). The call to that method happens in the "putBackIntoAvalonPool" case
in PoolableProxyHandler.invoke(). The problem is that this code will also be called *after*
the request attributes were set to null by the RequestContextListener, because it is registered
as a destruction callback, that gets called by Spring after the attribute reset.
> The real chain of calls is as follows:
>   RequestContextListener.requestDestroyed()
>   RequestContextHolder.setRequestAttributes(null)
>   callDestructionCallbacks()
>   <- which is a destruction callback
>   PoolableFactoryBean.putIntoPool()
>   PoolableFactoryBean.enteringPool()
>   component.recycle()
>   AvalonServiceManager/Selector.release(childComponent)   <- component releases its
>   AvalonPoolable.putBackIntoAvalonPool()
>   PoolableProxyHandler.invoke()   <- intercepts the putBackIntoAvalonPool() call
>   RequestContextHolder.currentRequestAttributes()   <-- Exception !!!

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