//src/include/mempool.h
shard_t* pick_a_shard() {
    // Dirt cheap, see:
    //   http://fossies.org/dox/glibc-2.24/pthread__self_8c_source.html
    size_t me = (size_t)pthread_self();
    size_t i = (me >> 3) & ((1 << num_shard_bits) - 1);
    return &shard[i];
  }
//src/common/mempool.cc
void mempool::pool_t::adjust_count(ssize_t items, ssize_t bytes)
{
  shard_t *shard = pick_a_shard();
  shard->items += items;
  shard->bytes += bytes;
}