when real FREE the memory in STL

Question

the STL's allocator use the memory pool tech, and it only add the memory needed deallocate into the free list, like this:

static void deallocate(void* __p, size_t __n)
{
    if (__n > (size_t) _MAX_BYTES)
    malloc_alloc::deallocate(__p, __n);
    else {
        _Obj* __STL_VOLATILE*  __my_free_list = _S_free_list + _S_freelist_index(__n);
        _Obj* __q = (_Obj*)__p;
        __q -> _M_free_list_link = *__my_free_list;
        *__my_free_list = __q;
    }
}

I want to know, when really FREE the free list?

Answer 1

There is no guarantee that the STL uses memory pools (although it is common).

It will depend on the implementation (compiler, library, version, OS, machine architecture, phase of the moon). A common answer is that memory allocated with new will only be returned to the operating system at program exit.