feat: rewrite wait_pids (Close #71)

riot/runtime/import.ml

@@ -181,10 +181,21 @@ let is_process_alive pid =
   | Some proc -> Process.is_alive proc
   | None -> false
 
-let rec wait_pids pids =
-  match pids with
-  | [] -> ()
-  | pid :: tail -> wait_pids (if is_process_alive pid then pids else tail)
+let wait_pids pids =
+  List.iter monitor pids;
+  let selector msg =
+    match msg with
+    | Process.Messages.Monitor (Process_down pid) when List.mem pid pids ->
+        `select Process.Messages.(Process_down pid)
+    | _ -> `skip
+  in
+  let rec do_wait pids =
+    match receive ~selector () with
+    | Process_down pid ->
+        let pids = List.filter (fun pid' -> not (Pid.equal pid' pid)) pids in
+        if List.length pids = 0 then () else do_wait pids
+  in
+  do_wait pids
 
 module Timer = struct
   type timeout = Util.Timeout.t

test/link_processes_test.ml

@@ -26,6 +26,8 @@ let main () =
         loop ())
   in
 
+  List.iter monitor [ pid1; pid2 ];
+
   sleep 0.5;
   (* once we send this exit signal to pid1, and it dies, it should take pid2 down with it *)
   exit pid1 Normal;

test/readme_example.ml

@@ -9,11 +9,9 @@ let () =
   Riot.run @@ fun () ->
   let pid =
     spawn (fun () ->
-      let selector msg = 
-        match msg with
-        | Hello_world -> `select `hello_world
-        | _ -> `skip 
-      in
+        let selector msg =
+          match msg with Hello_world -> `select `hello_world | _ -> `skip
+        in
         match receive ~selector () with
         | `hello_world ->
             Logger.info (fun f -> f "hello world from %a!" Pid.pp (self ()));