async callbacks in a loop

async.coffee

app.get '/riders', (req, res) ->
  redis.smembers 'riders', ( err, replies ) ->
  
    pool = new RequestPool ( rider, callback ) -> redis.hgetall rider, callback
  
    pool.push rider for rider in replies
  
    pool.go -> alert 'Done!'

request_pool.coffee

class RequestPool
  
  constructor : ( @block ) ->
    @responses = [ ]
    @requests  = [ ]
    
  push : ( request ) -> @requests.push request
  
  go : ( complete ) ->
    for request in @requests
      @block request, ( response ) ->

        @responses.push response

        complete @responses if @responses.length is @requests.length