Mailinglist Archive: zypp-devel (227 mails)

[Josef Reidinger <jreidinger@xxxxxxx>]

Jan Kupec wrote:
> I have the following experimental PoolQuery::ResultIterator
>
> extern "C"
> {
> #include "satsolver/repo.h";
> }
>
>   class PoolQuery
>   {
>   public:
>
>     typedef ::_Dataiterator RepoDataIterator;
>
>     class ResultIterator : public boost::iterator_adaptor<
>       ResultIterator                     // Derived
>       , RepoDataIterator *               // Base
>       , const sat::Solvable              // Value
>       , boost::forward_traversal_tag     // CategoryOrTraversal
>       , const sat::Solvable &            // Reference
>     >

I think that have query tight linked to result of some repo search is 
not good idea, because it prevent some optimalization (like now if 
someone want query on name and kind f.e. thunar and patch - you must 
search thrue all repository with this, but you can use name index on 
pool and have it significantly fast).
So I think better is use own storage for results (so you shade how you 
implement query search) and iterate over it.


>     {
>     public:
>       ResultIterator()
>       : ResultIterator::iterator_adaptor_(0)
>       { _rdit = 0; base_reference() = 0; }
>
>       ResultIterator(RepoDataIterator * rdit)
>       : ResultIterator::iterator_adaptor_(0)
>       { _rdit = rdit; base_reference() = rdit; }
>
>     private:
>       friend class boost::iterator_core_access;
>
>       sat::Solvable dereference() const
>       {
>         return _rdit ? sat::Solvable(_rdit->solvid) :
> sat::Solvable::noSolvable;
>       }
>
>       void increment()
>       {
>         if (::dataiterator_step(_rdit))
>         else
>         {
>           base_reference() = 0;
>         }
>       }
>
>       template <class OtherDerived, class OtherIterator, class V, class
> C, class R, class D>
>         bool equal( const boost::iterator_adaptor<OtherDerived,
> OtherIterator, V, C, R, D> & rhs ) const;
>       {
>         if (!rhs.base() && !base())
>           return true;
>         if (!rhs.base() || !base())
>           return false;
>         // quite useless since base() == rhs.base() always except for
>         // end()
>         if (rhs.base()->solvid == base()->solvid)
>           return true;
>         return false;
>       }
>
>     private:
>       RepoDataIterator * _rdit;
>     };
>
>   //  PoolQuery methods&members go here....
> }
>
> I use (maybe wrongly) the RepoDataIterator * as the base.
> RepoDataIterator is being created in PoolQuery::Impl, the begin() and
> end() methods look like this:
>
>   PoolQuery::ResultIterator PoolQuery::Impl::begin()
>   {
>     sat::Pool pool(sat::Pool::instance());
>     sat::Pool::RepositoryIterator itr = pool.reposBegin();
>     ::dataiterator_init(&_rdit, itr->get(), 0 /*p*/, 0/*keyname*/, 0
> /*matchstring*/, _flags);
>     INT << "next: " << ::dataiterator_step(&_rdit) << endl;
>     return PoolQuery::ResultIterator(&_rdit);
>   }

Little performance note - if you add flag dirty which is set to true 
everytime you change query settings and recreate result only if is set, 
then you can save some searching (for example if someone want two time 
iterate over same results).

>   PoolQuery::ResultIterator PoolQuery::Impl::end()
>   {
>     return PoolQuery::ResultIterator(0);
>   }
>
>
> This has (at least :O) two drawbacks:
>
> 1) RepoDataIterator * is the same in all instances except for those
>    created with PoolQuery::end()

if I understand it, own storage can help with this problem.

> 2) PoolQuery::begin() always resets the dataiterator state for all
>    existing instances

If used dirty flag, iterator is invalidate only when you change query 
settings.
If you don't want invalidate iterator you must have some iterator with 
reference counting pointer to old storage and always create dynamically 
new.

> This is probably a really bad evil. Can somebody (ma? :O) give me a
> pointer how to do it better? I would very much love to discover the
> world by myself, but the time is unfortunately running out :O(
>
> Please ignore the fact that this does not iterate across repositories
> for now; and that it iterates through solvable attributes, not just the
> solvables.
>
> cheers,
>
> jano

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