Function do_realloc_with_callback

libs/tcmalloc-1.4/src/tcmalloc.cc:705–743

This lets you call back to a given function pointer if ptr is invalid. It is used primarily by windows code which wants a specialized callback.

// This lets you call back to a given function pointer if ptr is invalid.
// It is used primarily by windows code which wants a specialized callback.
inline void* do_realloc_with_callback(
    void* old_ptr, size_t new_size,
    void (*invalid_free_fn)(void*),
    size_t (*invalid_get_size_fn)(void*)) {
  // Get the size of the old entry
  const size_t old_size = GetSizeWithCallback(old_ptr, invalid_get_size_fn);

  // Reallocate if the new size is larger than the old size,
  // or if the new size is significantly smaller than the old size.
  // We do hysteresis to avoid resizing ping-pongs:
  //    . If we need to grow, grow to max(new_size, old_size * 1.X)
  //    . Don't shrink unless new_size < old_size * 0.Y
  // X and Y trade-off time for wasted space.  For now we do 1.25 and 0.5.
  const unsigned int lower_bound_to_grow = old_size + old_size / 4;
  const unsigned int upper_bound_to_shrink = old_size / 2;
  if ((new_size > old_size) || (new_size < upper_bound_to_shrink)) {
    // Need to reallocate.
    void* new_ptr = NULL;

    if (new_size > old_size && new_size < lower_bound_to_grow) {
      new_ptr = do_malloc(lower_bound_to_grow);
    }
    if (new_ptr == NULL) {
      // Either new_size is not a tiny increment, or last do_malloc failed.
      new_ptr = do_malloc(new_size);
    }
    if (new_ptr == NULL) {
      return NULL;
    }
    memcpy(new_ptr, old_ptr, ((old_size < new_size) ? old_size : new_size));
    // We could use a variant of do_free() that leverages the fact
    // that we already know the sizeclass of old_ptr.  The benefit
    // would be small, so don't bother.
    do_free_with_callback(old_ptr, invalid_free_fn);
    return new_ptr;
  } else {
    return old_ptr;
  }
}

inline void* do_realloc(void* old_ptr, size_t new_size) {
  return do_realloc_with_callback(old_ptr, new_size,