How to use Lwt_pool

Question

I want to have a pool of Redis database connections with a max number of connections. It looks like Lwt_pool is the solution I am looking for, but I don't quite grasp how it should work. For example, some questions I have:

• The docs talk about Lwt_pool being great to reuse open connections, but how does the pool know what connections are available for reuse? As far as I see, there is no particular way to signal that and the API only provides the use method.

• Is there any resource better than the Lwt docs to learn how it works? I can't easily find code examples or many resources available about it.

Answer 1

• The function you pass to use returns a thread. When the thread finishes, the connection is released back to the pool.

• The source code is fairly easy to read. In this case:

  let use p f =
    acquire p >>= fun c ->
    Lwt.catch
      (fun () ->
         let t = f c in
         t >>= fun _ ->
         release p c;
         t)
      (fun e ->
         checked_release p c;
         Lwt.fail e)