Alternative to Sleep in Genserver


Hi everyone,

I’m quite new to Elixir.

I have a module using GenServer. The calling code calls a method that gets some data, and I want to have it wait for a period before responding, with the calling code blocking until it responds.

I’ve seen comments that Process.sleep() inside a genserver call is bad. I think because it blocks the genserver from responding to further calls?

Could someone help explain the alternatives?

Thanks a lot,



  • When you receive the message you want to delay processing, send_after another message to “yourself” that contains enough information to do the actual work - and do it when that message arrives.
  • Use :no_reply in your handle_* result (i.e. after the send_after has been processed).
  • You can use GenServer.reply/2 to reply to the caller at that later time.

Example here

Building Non Blocking Erlang apps discusses the approach in more detail - the code is in Erlang but it’s similar enough.


Thanks very much @peerreynders. What you described worked perfectly!