blockingQueue.js

blockingQueue = function(config) {

  // Don't require the use of a new keyword
  if (!this instanceof blockingQueue) {
    return new blockingQueue(config);
  }

  // Assume that this is attached to a UI activity so time out after 300ms
  var timeout = config && config.timeout ? config.timeout : 300;

  this.queue = [];

  return {
    queue: this.queue,

    // asyncDequeue is a boolean indicating function ownership of the dequeuing
    add: function(fn, config) {
      if (config && config.asyncDequeue) {
        fn.asyncDequeue = config.asyncDequeue;
      }

      if (typeof fn === 'function') {
        this.queue.push(fn);
        return this.queue.length;
      } else {
        return false;
      }

    },

    addAsync: function(fn) {
      this.add(fn, {asyncDequeue: true});
    },

    // Used publicly during dequeing of async functions
    remove: function(ix) {
      this.queue[ix] = null;
      return ix;
    },

    isEmpty: function() {
      var empty = true;
      for (var fn in this.queue) {
        if (this.queue[fn]) {
          empty = false;
          break;
        }
      }
      return empty;
    },

    // The core function controlling a blocking action like a form submission
    // is responsible for the final processing call
    process: function(cb) {

      var start = new Date();

      var that = this;

      for (var fn in this.queue) {
        try {
          if (this.queue[fn].asyncDequeue) {

            // Note a callback to dequeue this item
            // The canonical form for an async function is
            // addAsync(function(dq) { actions(); dq(); });
            this.queue[fn](
                function(ix) {
                  return function() {
                    that.remove(ix);
                  };
                }(fn)
            );

          } else {
            // Default case: force a dequeue through a callback
            this.queue[fn]();
            this.remove(fn);
          }
        } catch (x) {
          // Explicitly dequeue the function if we have an error
          this.remove(fn);
        }
      }

      // Poll to see if we have to finish before our timeout
      var poll = setInterval(
          function() {
            var diff = new Date() - start;
            if (that.isEmpty() || diff > timeout) {

              clearInterval(poll);
              if (typeof cb === 'function') {
                cb();
              }
            }
          },
          25
          );

    }

  };
};