code: synchronized void collectPages(Collection<Long> offsets, Collection<PageWrapper> target) {
          offsets.forEach(offset -> {
              PageWrapper p = this.pageByOffset.getOrDefault(offset, null);
              if (p != null) {
                  target.add(p);
              }
          });
      }
docs: Collects the PageWrappers with given offsets into the given Collection.
  
  @param offsets A Collection of offsets to collect PageWrappers for.
  @param target  The Collection to collect into.