CP-32622: Replace select with polly in child

ocaml/forkexecd/src/child.ml

@@ -59,28 +59,42 @@ let handle_comms_sock comms_sock state =
       state
 
 let handle_comms_no_fd_sock2 comms_sock fd_sock state =
-  debug "Selecting in handle_comms_no_fd_sock2" ;
-  let ready, _, _ = Unix.select [comms_sock; fd_sock] [] [] (-1.0) in
-  debug "Done" ;
-  if List.mem fd_sock ready then (
-    debug "fd sock" ;
-    let fd_sock2, _ = Unix.accept fd_sock in
-    {state with fd_sock2= Some fd_sock2}
-  ) else (
-    debug "comms sock" ;
-    handle_comms_sock comms_sock state
+  debug "Using epoll in handle_comms_no_fd_sock2" ;
+  let epoll = Polly.create () in
+  List.iter
+    (fun fd -> Polly.add epoll fd Polly.Events.inp)
+    [comms_sock; fd_sock] ;
+  (* Although there are two fds, we set max_fds to 1 here as we only want this
+     function to trigger once so that we get one return value *)
+  Polly.wait_fold epoll 1 (-1) state (fun _ fd _ _ ->
+      debug "Done" ;
+      if fd_sock = fd then (
+        debug "fd sock" ;
+        let fd_sock2, _ = Unix.accept fd_sock in
+        {state with fd_sock2= Some fd_sock2}
+      ) else (
+        debug "comms sock" ;
+        handle_comms_sock comms_sock state
+      )
   )
 
 let handle_comms_with_fd_sock2 comms_sock _fd_sock fd_sock2 state =
-  debug "Selecting in handle_comms_with_fd_sock2" ;
-  let ready, _, _ = Unix.select [comms_sock; fd_sock2] [] [] (-1.0) in
-  debug "Done" ;
-  if List.mem fd_sock2 ready then (
-    debug "fd sock2" ;
-    handle_fd_sock fd_sock2 state
-  ) else (
-    debug "comms sock" ;
-    handle_comms_sock comms_sock state
+  debug "Using epoll in handle_comms_with_fd_sock2" ;
+  let epoll = Polly.create () in
+  List.iter
+    (fun fd -> Polly.add epoll fd Polly.Events.inp)
+    [comms_sock; fd_sock2] ;
+  (* Although there are two fds, we set max_fds to 1 here as we only want this
+     function to trigger once so that we get one return value *)
+  Polly.wait_fold epoll 1 (-1) state (fun _ fd _ _ ->
+      debug "Done" ;
+      if fd_sock2 = fd then (
+        debug "fd sock2" ;
+        handle_fd_sock fd_sock2 state
+      ) else (
+        debug "comms sock" ;
+        handle_comms_sock comms_sock state
+      )
   )
 
 let handle_comms comms_sock fd_sock state =

ocaml/forkexecd/src/dune

@@ -5,6 +5,7 @@
    astring
    fd-send-recv
    forkexec
+   polly
    systemd
    uuid
    xapi-log