I'm going to develop an appointment remindig system,which is a web based application.One of its important functions is to pop up a window at some certain time to remind the user for an coming appointment .

So I think there're 2 options to implement this requirement:

1.Refresh page automatically in a certain interval.

2.set up a daemon thread to moniter all appointments which should be stored in a database,when there's an appointment coming,this thread send a message to front end to pop up a window.

Do you gus think option 1 is good idea?

And for option 2, I got something troublesome, how can I send a message from server to a client browser without a http request from this client browser?

Please answer these for me ,thank you in advance.