On 10 Jun 2009, at 22:08, Thorsten Ottosen wrote:
Christopher Jefferson skrev:
Very interesting. I have been working on a similar, but much more limited, proposal which just does this for vector. I decided I had to implement a new class, because building on top of the 'allocator' framework wasn't sensible, because you waste too much buffer space. For example, I believe your example won't work. I'd be interested to see what you think. Consider your example, in g++ (which I know how it operates internally) boost::monotonic::inline_storage<100*sizeof(Object)> storage; // create local storage on the stack boost::monotonic::vector<Object> deathrow(storage); // create a std::vector that uses this storage foreach (object in world) { if (IsDead(object)) deathrow.push_back(object); // allocation is just advancing a pointer } This will build a vector which will continuously expand, through sizes 1,2,4,8,16,32. At each step, it will allocate a new block of memory and free the old one, making the storage size 1,3,7,15,31,63. When we try to push_back beyond 32 elements, the next allocation will overflow the buffer. Am I missing something?
Maybe
http://www.cs.aau.dk/~nesotto/boost/trunk/libs/auto_buffer/doc/html/ http://www.cs.aau.dk/~nesotto/boost/trunk/boost/auto_buffer/
is what you are looking for?
That doesn't do exactly what I want for two reasons, but most might be fixable. 1) I want run-time variable amounts of space (this does involve some alloca, and probably macro, hackery). 2) I want it to be an error if it is necessary to go to the heap. For (1) I use a macro something like: #define GET_ALLOCA_MEM(type, x) box<type>(x, alloca(x * sizeof(type)) Because obviously you can't call alloca inside the auto_buffer constructor. Chris