Title here
Summary here
Closing Channels in OCaml
In this example, we’ll demonstrate how to close channels in OCaml using the Event module from the Lwt library. Closing a channel indicates that no more values will be sent on it. This can be useful to communicate completion to the channel’s receivers.
open Lwt
open Lwt_channel
let main () =
let jobs = Lwt_channel.create_bounded 5 in
let done_signal = Lwt_mvar.create_empty () in
let worker () =
let rec loop () =
Lwt_channel.recv jobs >>= function
| Some j ->
Lwt_io.printf "received job %d\n" j >>= loop
| None ->
Lwt_io.printl "received all jobs" >>= fun () ->
Lwt_mvar.put done_signal true
in
loop ()
in
let _ = worker () in
let send_jobs () =
let rec send_job j =
if j <= 3 then
Lwt_channel.send jobs j >>= fun () ->
Lwt_io.printf "sent job %d\n" j >>= fun () ->
send_job (j + 1)
else
Lwt.return_unit
in
send_job 1 >>= fun () ->
Lwt_channel.close jobs >>= fun () ->
Lwt_io.printl "sent all jobs"
in
send_jobs () >>= fun () ->
Lwt_mvar.take done_signal >>= fun _ ->
Lwt_channel.recv jobs >>= function
| Some _ -> Lwt_io.printl "received more jobs: true"
| None -> Lwt_io.printl "received more jobs: false"
let () = Lwt_main.run (main ())In this OCaml version, we use Lwt_channel to create a bounded channel for jobs and Lwt_mvar for synchronization. The worker function repeatedly receives from the jobs channel until it’s closed, then signals completion through the done_signal mvar.
We send 3 jobs to the worker over the jobs channel, then close it. We await the worker using the synchronization approach with Lwt_mvar.
Finally, we attempt to receive from the closed channel to demonstrate that it returns None when closed.
To run this program, you would save it as closing_channels.ml and compile it with the Lwt library:
$ ocamlfind ocamlc -package lwt,lwt.unix -linkpkg -o closing_channels closing_channels.ml
$ ./closing_channels
sent job 1
received job 1
sent job 2
received job 2
sent job 3
received job 3
sent all jobs
received all jobs
received more jobs: falseThis example demonstrates how to use channels and synchronization primitives in OCaml with the Lwt library, which provides a concurrent programming model similar to goroutines in Go.