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From Ruediger Pluem <rpl...@apache.org>
Subject Re: svn commit: r821477 - in /httpd/httpd/trunk: CHANGES modules/http/byterange_filter.c modules/http/http_filters.c server/core_filters.c
Date Sun, 04 Oct 2009 10:14:34 GMT


On 10/04/2009 10:54 AM, Stefan Fritsch wrote:
> On Sunday 04 October 2009, Paul Querna wrote:
>>> URL: http://svn.apache.org/viewvc?rev=821477&view=rev
>>> Log:
>>> Make sure to not destroy bucket brigades that have been created
>>> by earlier filters. Otherwise the pool cleanups would be removed
>>> causing potential memory leaks later on.
>> I am not sure these changes make sense.  The 'traditional' API view
>> says that brigades passed down the output fitler chain should be
>> destroyed, not cleared -- please see the thread started with this
>> message:
>> <http://mail-archives.apache.org/mod_mbox/httpd-dev/200504.mbox/%3C
>> 9ccfb16df2220fc31c836bb7cd640554@ricilake.net%3E>
>>
> 
> This is at odds with the documentation at 
> http://httpd.apache.org/docs/trunk/developer/output-filters.html , in 
> particular with rules 6 and 9 at the end. If output filters reuse 
> brigades, the core must not destroy them.
> 
> I just noticed that include/util_filter.h still says "The caller 
> relinquishes ownership of the brigade" for ap_pass_brigade(). Either 
> output-filters.html or util_filter.h must be changed.
> 
> In my opinion, it is much better to not destroy the brigades and reuse 
> them instead of creating a new brigade on every filter invocation. 
> Otherwise there is huge memory usage for streaming content.
> 
> The thread you have pointed out also has a suggested patch for the 
> docs in util_filter.h:
> 
> http://mail-archives.apache.org/mod_mbox/httpd-
> dev/200504.mbox/<20050426102834.GE16976@redhat.com>
> 
> It is not clear from the thread why it wasn't applied.

>From rereading the old discussion back in 2005 I guess it is the correct
thing to fix the comment in util_filter.h and not to destroy brigades that
weren't created by us but just to clean them up.
So the ownership of the brigade remains with the creator / caller, whereas the
ownership of the buckets is transferred (either consume them directly or put them
safely aside for later consumption).
Regarding adding an apr_brigade_cleanup call to ap_pass_brigade I am undecided.

Regards

RĂ¼diger



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