mutex.js

var Mutex = function() {
  this.queues = [];
  this.locked = false;
};

Mutex.prototype = {
  push: function(callback) {
    var self = this;
    this.queues.push(callback);
    if (!this.locked) {
      this.locked = true;

      var f = this.queues.pop();
      try {
        f(function() {
          self.locked = false;
        });
      } catch(ex) {
        self.locked = false;
      }
    }
  }
};