promise_upload.js

function upload(stream, idOrPath, tag) {
  var queries = new Array(global.parallelQueries);
  var tx = db.begin();
  when.map(queries, insert).catch(rollback);
  tx.commit();
  
  function insert(query) {
    FileVersion.insert({index: i}).execWithin(tx, query);
  }
  
  function rollback () {
    tx.rollback();
  }
}

task_upload.js

task upload(stream, idOrPath, tag) {
    var queries = new Array(global.parallelQueries),
        tx = db.begin();

    catch (e) {
        tx.rollback();
    }

    var ch = new Channel();

    for (var i = 0, len = queries.length; i < len; ++i) {
        FileVersion.insert({index: i}).execWithin(tx, ch.receive(i));
    }

    await ch.takeN(queries.length);

    tx.commit();
}