code: function someAsyncFunction(file, callback) {
      // Here we just wrap the function body to make it synchronous inside
      // Sync will execute first argument 'fn' in synchronous way
      // and call second argument 'callback' when function returns
      // it also calls callback if exception will be thrown inside of 'fn'
      Sync(function(){
          var source = require('fs').readFile.sync(null, __filename);
          return source;
      }, callback)
  }
docs: Simple asynchronous function with fiber inside example