Method FetchFromCentralCache

libs/tcmalloc-1.4/src/thread_cache.cc:154–186

Remove some objects of class "cl" from central cache and add to thread heap. On success, return the first object for immediate use; otherwise return NULL.

// Remove some objects of class "cl" from central cache and add to thread heap.
// On success, return the first object for immediate use; otherwise return NULL.
void* ThreadCache::FetchFromCentralCache(size_t cl, size_t byte_size) {
  FreeList* list = &list_[cl];
  ASSERT(list->empty());
  const int batch_size = Static::sizemap()->num_objects_to_move(cl);

  const int num_to_move = min<int>(list->max_length(), batch_size);
  void *start, *end;
  int fetch_count = Static::central_cache()[cl].RemoveRange(&start, &end, num_to_move);

  ASSERT((start == NULL) == (fetch_count == 0));
  if (--fetch_count >= 0) {
    size_ += byte_size * fetch_count;
    list->PushRange(fetch_count, SLL_Next(start), end);
  }

  // Increase max length slowly up to batch_size.  After that,
  // increase by batch_size in one shot so that the length is a
  // multiple of batch_size.
  if (static_cast<int>(list->max_length()) < batch_size) {
    list->set_max_length(list->max_length() + 1);
  } else {
    // Don't let the list get too long.  In 32 bit builds, the length is represented by a 16 bit int, so we need to watch out
    // for integer overflow.
    int new_length = min<int>(list->max_length() + batch_size, kMaxDynamicFreeListLength);
    
    // The list's max_length must always be a multiple of batch_size, and kMaxDynamicFreeListLength is not necessarily a
    // multiple of batch_size.
    new_length -= new_length % batch_size;
    ASSERT(new_length % batch_size == 0);
    list->set_max_length(new_length);
  }
  return start;
}

void ThreadCache::ListTooLong(FreeList* list, size_t cl) {
  const int batch_size = Static::sizemap()->num_objects_to_move(cl);