sequence-schedule.js

  var lockMonitor = {};

  function schedule(messageKey, callback) {

    function run(messageObject, trace, deferred) {
      var lockKey = messageObject[messageKey];
      if (!lockMonitor[lockKey]) {
        lockMonitor[lockKey] = true;
        var result = callback(messageObject, trace);
        deferred.resolve(result);
        Q(result).then(function() {
          delete lockMonitor[lockKey];
        });
      } else {
        setTimeout(run, 50, messageObject, trace, deferred);
      }
    }

    return function(messageObject, trace) {
      var deferred = Q.defer();
      run(messageObject, trace, deferred);
      return deferred.promise;
    };
  }