code: public void markCanBeCompleted(long id) {
      Long opId = id;
      completedOperationIds.offerLast(opId);
      Long start = starTimes.remove(opId);
      if (start != null) {
        stats.markRpcComplete(clock.nanoTime() - start);
      }
    }
docs: Mark an operation id, as returned by {@code registerOperationWithHeapSize}, as complete
  
  @param id a long.