[Nepomuk] Nepomuk Core - Questions & Patches

[Sebastian Trüg]

Hm, I think I found a situation where this could still fail:

Imagine this scenario:

the store contains resource n:/res/foo with identifier "foo"

We then use this code in one thread:

Resource r1(QUrl("n:/res/foo"));
Resource r2("foo");

and this in another:

Resource r3("foo");

Now imagine for some reasons r1's determineUrl() has been called
already, thus, calling it on r2 or r3 would result in a replace. So far
so good.
But what if both thread would try it at the same time? One of them would
perform the determineUrl() and ultimately delete the ResourceData (which
is referenced by both r2 and r3). At the same time r3's thread would
wait for the mutex in determinUrl() to be released and then try to
execute the method in the deleted ResourceData -> crash!

Cheers,
Sebastian

On 05/27/2010 01:59 PM, Sebastian Trüg wrote:
> Hi Vishesh,
> 
> I finally looked at the remove-proxy patch again and fixed it. Now the
> only problem left is the design weirdness of ResourceData instances
> deleting themselves.
> 
> The main thing I did was removing all calls to determineUri from
> ResourceData and moving them into Resource. I did the same with load()
> and store() which is actually not necessary. Maybe it would be cleaner
> to move those back...
> 
> I did not look into the merging of load and determineUri yet. I think we
> should do that in a separate patch only after we cleaned this one up.
> Otherwise it is impossible to debug.
> 
> Cheers,
> Sebastian
> 
> On 05/26/2010 12:52 PM, Vishesh Handa wrote:
>>
>>
>> On Wed, May 26, 2010 at 3:13 PM, Sebastian Trüg <trueg at kde.org
>> <mailto:trueg at kde.org>> wrote:
>>
>>     On 05/26/2010 10:08 AM, Vishesh Handa wrote:
>>     >     > 3. When checking if the the m_kickoffUri is a nie:url for a
>>     resource.
>>     >     > The nieUrl is assigned to be equal to the uri. This however
>>     gets fixed
>>     >     > in the load(). And nieUrl isn't used anywhere, so it doesn't
>>     >     matter that
>>     >     > much.
>>     >
>>     >     I suppose you mean this part:
>>     >
>>     >     if( it.next() ) {
>>     >          QUrl uri = it["r"].uri();
>>     >          if( uri.isEmpty() ) {
>>     >             m_uri = m_kickoffUri;
>>     >          }
>>     >          else {
>>     >             m_uri = uri;
>>     >             m_nieUrl = uri;
>>     >          }
>>     >
>>     >     The last two lines. AFAICT this is perfectly fine since in the
>>     latter
>>     >     case both nie:url and resource URI are equal.
>>     >
>>     >
>>     > I respectfully disagree. :)
>>     >
>>     > The query used is this "select distinct ?r ?o where { { ?r nie:url
>>     <uri>
>>     > . } UNION { <uri> ?p ?o . }  } LIMIT 1". The case where ?r isn't empty
>>     > is when the <uri> contains the nie:url and therefore ?r will
>>     contain the
>>     > resource uri.
>>
>>     You are of course correct. It should be "m_nieUrl = m_kickoffUri"
>>     instead. Agreed?
>>
>>
>> Yup. :)
>>
>> If you get the time could you please look at my horrible merge patch?
>>
>> Thanks
>> - Vishesh Handa
>>
>>     Cheers,
>>     Sebastian
>>
>>
>>
>>
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