CP-32622: avoid using select and instead use epoll

ocaml/libs/http-svr/buf_io.ml

@@ -79,14 +79,17 @@ let is_full ic = ic.cur = 0 && ic.max = Bytes.length ic.buf
 let fill_buf ~buffered ic timeout =
   let buf_size = Bytes.length ic.buf in
   let fill_no_exc timeout len =
-    let l, _, _ = Unix.select [ic.fd] [] [] timeout in
-    if List.length l <> 0 then (
-      let n = Unix.read ic.fd ic.buf ic.max len in
-      ic.max <- n + ic.max ;
-      if n = 0 && len <> 0 then raise Eof ;
-      n
-    ) else
-      -1
+    Unix.setsockopt_float ic.fd Unix.SO_RCVTIMEO timeout ;
+    let result =
+      try
+        let n = Unix.read ic.fd ic.buf ic.max len in
+        ic.max <- n + ic.max ;
+        if n = 0 && len <> 0 then raise Eof ;
+        n
+      with Unix.Unix_error (Unix.EAGAIN, _, _) -> -1
+    in
+    Unix.setsockopt_float ic.fd Unix.SO_RCVTIMEO 0. ;
+    result
   in
   (* If there's no space to read, shift *)
   if ic.max = buf_size then shift ic ;

ocaml/libs/stunnel/stunnel.ml

@@ -394,7 +394,7 @@ let rec retry f = function
     try f ()
     with Stunnel_initialisation_failed ->
       (* Leave a few seconds between each attempt *)
-      ignore (Unix.select [] [] [] 3.) ;
+      Thread.delay 3. ;
       retry f (n - 1)
   )
 

ocaml/squeezed/src/squeeze_xen.ml

@@ -572,7 +572,7 @@ let make_host ~verbose ~xc =
       1024L
     <> 0L
   do
-    ignore (Unix.select [] [] [] 0.25)
+    Thread.delay 0.25
   done ;
 
   (* Some VMs are considered by us (but not by xen) to have an
@@ -857,7 +857,7 @@ let io ~xc ~verbose =
       (fun domid kib ->
         execute_action ~xc {Squeeze.action_domid= domid; new_target_kib= kib}
       )
-  ; wait= (fun delay -> ignore (Unix.select [] [] [] delay))
+  ; wait= (fun delay -> Thread.delay delay)
   ; execute_action= (fun action -> execute_action ~xc action)
   ; target_host_free_mem_kib
   ; free_memory_tolerance_kib

ocaml/xe-cli/newcli.ml

@@ -633,7 +633,7 @@ let main_loop ifd ofd permitted_filenames =
           with
           | Unix.Unix_error (_, _, _)
             when !delay <= long_connection_retry_timeout ->
-              ignore (Unix.select [] [] [] !delay) ;
+              Thread.delay !delay ;
               delay := !delay *. 2. ;
               keep_connection ()
           | e ->

ocaml/xenopsd/cli/xn.ml

@@ -1214,7 +1214,7 @@ let raw_console_proxy sockaddr =
         (fun () -> Unix.close s)
     with
     | Unix.Unix_error (_, _, _) when !delay <= long_connection_retry_timeout ->
-        ignore (Unix.select [] [] [] !delay) ;
+        Thread.delay !delay ;
         delay := !delay *. 2. ;
         keep_connection ()
     | e ->

ocaml/xenopsd/xc/memory_breakdown.ml

@@ -246,7 +246,7 @@ let print_memory_field_values xc xs =
   flush stdout
 
 (** Sleeps for the given time period in seconds. *)
-let sleep time_period_seconds = ignore (Unix.select [] [] [] time_period_seconds)
+let sleep time_period_seconds = Thread.delay time_period_seconds
 
 (** Prints a header line of memory field names, and then periodically prints a
     line of memory field values. *)

ocaml/xenopsd/xc/memory_summary.ml

@@ -36,7 +36,7 @@ let _ =
   let finished = ref false in
   while not !finished do
     finished := !delay < 0. ;
-    if !delay > 0. then ignore (Unix.select [] [] [] !delay) ;
+    if !delay > 0. then Thread.delay !delay ;
     flush stdout ;
     let physinfo = Xenctrl.physinfo xc in
     let one_page = 4096L in