code: private Task<Exec.Result> getBuildTask(final String hash, final InputStream body) {
      Task<Exec.Result> existing = _inFlightBuildTasks.get(hash);
      if (existing != null) {
        LOG.info("using in flight shareable: " + hash);
        return existing.shareable();
      } else {
        Task<Exec.Result> newBuildTask = createNewBuildTask(hash, body);
        existing = _inFlightBuildTasks.putIfAbsent(hash, newBuildTask);
        if (existing != null) {
          LOG.info("using in flight shareable: " + hash);
          return existing.shareable();
        } else {
          return newBuildTask;
        }
      }
    }
docs: Returns task that builds graph using graphviz. Returned task might be shared with other concurrent requests.