Re: [Boost-users] Mersenne twister problem

Subject: Re: [Boost-users] Mersenne twister problem
From: ruya (rmlopes_at_[hidden])
Date: 2009-09-18 05:30:24

Hi

The problem was the missing copy constructor, which I usually write by
default but for some reason had it commented. I still don't understand why
it didn't happened with the remaining algorithms but anyway, thank you for
the help on the fault.
Now, for the code refactoring, if the generator is static all SFs will share
the same generator and the distributions will not be independent anymore,
which is a requisite in this kind of algorithm. 

Regards
Rui Lopes

Matthias Troyer-2 wrote:
> 
> 
> On 17 Sep 2009, at 17:11, ruya wrote:
> 
>>
>>
>> Matthias Troyer-2 wrote:
>>>
>>>
>>> On 16 Sep 2009, at 10:38, ruya wrote:
>>>
>>>>
>>>> SType is not a SearchFunctor. It is a template parameter of
>>>> SearchFunctor.
>>>> Look, I am not a professional coder or something. I could accept
>>>> that my
>>>> code has memory leaks, except that I monitored the memory usage and
>>>> it is
>>>> stable and quite small too. I have three other algorithms using the
>>>> same
>>>> SearchFunctors and the behavior is as expected and no memory leaks.
>>>> As for the complication that my code appears to be to you, how would
>>>> you
>>>> simplify it? You argued before that you would do it diferently and
>>>> avoid for
>>>> sure the segmentation fault.
>>>>>>
>>>>>>  SearchFunctor(){
>>>>>>    memh = MemHandler();
>>>>>>    generator1 = base_generator_type(MASTER_SEED+13);
>>>>>>    uni_dist1 = boost::uniform_real<>(0,1);
>>>>>>    uniEmp = new GeneratorI(generator1, uni_dist1);
>>>>>>    generator2 = base_generator_type(MASTER_SEED+17);
>>>>>>    uni_dist2 = boost::uniform_real<>(0,1);
>>>>>>    uniRes = new GeneratorI(generator2, uni_dist2);
>>>>>>  }
>>>>>> protected:
>>>>>>  virtual ~SearchFunctor(){}
>>>
>>> Just look at this code fragment: you allocate memory in the
>>> constructor using new and never release it using delete
>>>
>>>
>>
>> I probably don't see this leak in the memory usage because only a  
>> limited
>> amount of SearchFunctors are created at the beginning and they live  
>> for as
>> long as the program runs. (I think this makes sense)
>> Anyhow, writing the proper destructors doesn't solve my problem, but  
>> now gdb
>> points to immediatly before the creation of any of the  
>> SearchFunctors. So,
>> to remember, I have three SearchFunctors (SFs). In three different
>> applications the three of them work as expected. In this particular  
>> app, the
>> SFs were successfully created, then two ran well, and one would give  
>> a seg
>> fault. Now, with the proper destructor in class SearchFunctor, the  
>> fault
>> comes at the time of creation. gdb points to the line where the  
>> following
>> functions is called:
>>
>>
>> functors = vector<SearchF>();
>> TL2FunV<TList, SearchF>::FillVector( functors ); //gdb points fault  
>> here but
>> does not go inside
>>
>>  template< typename TList, class SearchFun >
>>  struct TL2FunV{
>>    static void FillVector( std::vector< SearchFun >& v){
>>      typename TList::Head h;
>>      v.push_back( SearchFun(h) );
>>      TL2FunV<typename TList::Tail, SearchFun>::FillVector( v );
>>    }
>>  };
>>
>>  template< class SearchFun >
>>  struct TL2FunV< Loki::NullType, SearchFun>{
>>    static void FillVector( std::vector< SearchFun >& v ){};
>>  };
>>
>> Rui
>>
> 
> Since you use pointers inside your class you also need to write a copy  
> constructor and assignment operator creating new generators. I now  
> understand the reason for your crash:
> 
> - you create a SearchFunctor, this creates the engine as a member and  
> the generators through pointers
> - you copy the SearchFunctor in the FillVector function. Using the  
> implicitly generated copy constructor this just copies the pointers
> - after copying the original class gets destroyed - including the  
> random number engine.
> - you call the generator, but the engine no longer exists ->  
> segmentation fault.
> 
> Whenever you allocate memory on a constructor you need to provide a  
> special destructor, copy constructor and assignment operator. Either  
> add those, or - much easier, just use the following class:
> 
> template< class SType, typename MemP >
> class SearchFunctor{
> protected:
>    typedef boost::mt19937 base_generator_type;
>    typedef boost::variate_generator<base_generator_type,  
> boost::uniform_real<> > GeneratorI;
> public:
> 
>    SearchFunctor()
>      : uniEmp(base_generator_type(MASTER_SEED+13),boost::uniform_real<> 
> (0,1))
>      , uniRes(base_generator_type(MASTER_SEED+17),boost::uniform_real<> 
> (0,1))
>    {}
> 
> protected:
>    virtual ~SearchFunctor(){}
> 
>    GeneratorI uniEmp;
>    GeneratorI uniRes;
> }
> 
> 
> Note that I removed the & after the generator type to avoid a problem  
> with the copy constructor. Better yet, make the generator a static  
> class member and use the &:
> 
> 
> template< class SType, typename MemP >
> class SearchFunctor{
> protected:
>    typedef boost::mt19937 base_generator_type;
>    typedef boost::variate_generator<base_generator_type&,
> boost::uniform_real<> > GeneratorI;
> public:
> 
>    SearchFunctor()
>      : uniEmp(generator,boost::uniform_real<>(0,1))
>      , uniRes(generator,boost::uniform_real<>(0,1))
>    {}
> 
> protected:
>    virtual ~SearchFunctor(){}
>    GeneratorI uniEmp;
>    GeneratorI uniRes;
> private:
>    static base_generator_type generator;
> }
> 
> template< class SType, typename MemP >
> typename SearchFunctor< SType, MemP>::base_generator_type  
> SearchFunctor< SType, MemP>::generator(MASTER_SEED);
> 
> 
> 
> Matthias
> 
> 
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> 
> 

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