Allocated block expansion without relocation

[viccpp]

Hello!

It would be good to have some function like realloc() that tries to expand/shrink allocated memory buffer but doesn't try to relocate the block, just returns unsuccessful status when in place reallocation is impossible.

The idea is explained in detail here (it's a proposal for ISO C++).

As examples of a possible solution:

jemalloc has xmallocx() function with the required behaviour (also it returns the real size of the resulting resized allocation as requested in #2).

Windows HeapReAlloc() function has HEAP_REALLOC_IN_PLACE_ONLY flag.

[daanx]

Thanks for your feedback. The function mi_expand seems to do what you suggest.

[viccpp]

AFAICS this function doesn't try to expand anything, just tries to reuse extra allocated space:

void* mi_expand(void* p, size_t newsize) mi_attr_noexcept {
  if (p == NULL) return NULL;
  size_t size = mi_usable_size(p);
  if (newsize > size) return NULL;
  return p; // it fits
}

Could we have true implementation? Does the library support allocated block expansion at all?

[daanx]

Ah I see what you mean. However, the current design often does have more space available. But at the same time, the design is based on size segregated areas so it does not support further in-place expanding of blocks (well, perhaps we could support it for huge objects).