[Coin-discuss] BCP_vec<double> memory allocation

[Laszlo Ladanyi]

The answer is both... Intended behavior and bug. Intended, because I wanted to
allocate enough memory so that vectors of size around 10-100 (which in my 
guess are the most frequent sizes) would not need any reallocation. The 0x1000
is probably a bug, it is way more then is necessary, I think. Probably I
wanted 0x100. Also, the * sizeof(double) is a bug, since it makes no sense to
multiply with teh size of the object both in push_back and in allocate.

I have fixed both sort of bug and committed the changes.

--Laci

On Mon, 25 Oct 2004, Daniel Lichtenberger wrote:

> Hi!
> 
> I'm using COIN/Bcp to build a local branching framework, and I've run into 
> problems using lots of BCP_vec<double> objects (or storing many objects 
> containing BCP_vec<double> objects, like BCP_solution_generic). The program 
> segfaults after allocating a few thousand objects. I looked through the Bcp 
> sources, and noticed that BCP_vec<double> allocates a lot of memory in 
> advance - so much that even virtual memory seems to run out.
> 
> In
> BCP_vec<double>::insert_aux(iterator position, const_reference x)
> these lines seem to allocate extra memory when the container gets too small 
> (BCP_vector_double.cpp):
> 
>       const size_t len = (2*size() + 0x1000) * sizeof(double);
>       iterator tmp = allocate(len);
> 
> allocate is defined in BCP_vector.hpp:
> 
>    inline iterator allocate(size_t len) {
>       return static_cast<iterator>(::operator new(len * sizeof(T)));
>    }
>  
> So when a BCP_vec<double> runs out of space, it allocates at least 
> 0x1000 * 8 * 8 = 256 kb of memory (assuming a double is 8 bytes). Since a 
> BCP_vec is initialized with a capacity of 0, each BCP_vec<double> takes 256 
> KB once a value has been inserted, like:
> 
>         BCP_vec<double>* v = new BCP_vec<double>;
>         v->push_back(1);
> 
> I've run some quick tests that seem to back this assumption (on my x86 
> machine). Is this a bug or intended behaviour?
> 
> Thanks,
> Daniel
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