Improve traces

README.md

@@ -220,70 +220,30 @@ Calling an operation that performs an effect (such as `yield`) can switch to a d
 When OCaml's tracing is turned on, Eio writes events about many actions,
 such as creating fibers or resolving promises.
 
-[examples/trace](./examples/trace/) shows how to consume the events manually:
+You can use [eio-trace][] to capture a trace and display it in a window.
+For example, this is a trace of the counting example above:
 
-<!-- $MDX skip -->
-```sh
-$ dune exec -- ./examples/trace/main.exe
-+tracer: starting                      
-30926487700447:ring 0: create fiber 0
-30926487702032:ring 0: running fiber 0
-30926487705057:ring 0: create switch 1
-30926487707264:ring 0: create fiber 2
-30926487707512:ring 0: running fiber 2
-30926487720213:ring 0: log "tracer: starting"
-+server: starting
-+client: connecting socket...
-+server: got connection from client
-+server: read "Hello" from socket
-30926487769298:ring 0: running fiber 0
-30926487769877:ring 0: create fiber 3
-30926487770083:ring 0: running fiber 3
-30926487771198:ring 0: create switch 4
-30926487807888:ring 0: create switch 5
-30926487808329:ring 0: create fiber 6
-30926487808555:ring 0: running fiber 6
-30926487812219:ring 0: log "server: starting"
-30926487818883:ring 0: running fiber 3
-30926487819091:ring 0: create fiber 7
-30926487819155:ring 0: running fiber 7
-30926487822428:ring 0: log "client: connecting socket..."
-30926487901604:ring 0: running fiber 3
-30926487904947:ring 0: running fiber 0
-30926487907318:ring 0: running fiber 6
-30926487917202:ring 0: log "server: got connection from client"
-30926487929993:ring 0: running fiber 6
-30926487941403:ring 0: running fiber 7
-30926487948000:ring 0: running fiber 7
-30926487971898:ring 0: resolve 7
-30926487974810:ring 0: running fiber 6
-30926487975215:ring 0: running fiber 6
-30926487977869:ring 0: running fiber 6
-30926487984514:ring 0: log "server: read \"Hello\" from socket"
-30926487990785:ring 0: resolve 6
-30926487991752:ring 0: running fiber 3
-30926488022310:ring 0: resolve 3
-30926497839725:ring 0: running fiber 2
-+tracer: stopping
 ```
+dune build ./examples
+eio-trace run -- ./_build/default/examples/both/main.exe
+```
+
+<p align='center'>
+  <img src="./doc/traces/both-posix.svg"/>
+</p>
 
+The upper horizontal bar is the initial fiber, and the brackets show `Fiber.both` creating a second fiber.
+The green segments show when each fiber is running.
 Note that the output from `traceln` appears in the trace as well as on the console.
+In the eio-trace window, scrolling with the mouse or touchpad will zoom in or out of the diagram.
 
-There are various third-party tools that can consume this data
+There are various third-party tools that can also consume this data
 (but may currently require patches to support the new system):
 
 - [Meio][] (Monitoring for Eio) provides an interactive console-based UI for exploring running fibers.
 - [Olly][] can save Perfetto traces and report statistics.
-- [mirage-trace-viewer][] renders traces visually.
-
-For example, this is how mirage-trace-viewer renders the counting example above:
-
-<p align='center'>
-  <img src="./doc/trace.svg"/>
-</p>
 
-This shows the two counting threads as two horizonal lines.
-The white regions indicate when each thread was running.
+[examples/trace](./examples/trace/) shows how to consume the events manually.
 
 ## Cancellation
 
@@ -1893,3 +1853,4 @@ Some background about the effects system can be found in:
 [Eio.Process]: https://ocaml-multicore.github.io/eio/eio/Eio/Process/index.html
 [Dev meetings]: https://docs.google.com/document/d/1ZBfbjAkvEkv9ldumpZV5VXrEc_HpPeYjHPW_TiwJe4Q
 [Olly]: https://github.com/tarides/runtime_events_tools
+[eio-trace]: https://github.com/ocaml-multicore/eio-trace

doc/traces/Makefile

@@ -0,0 +1,2 @@
+all:
+	eio-trace render -f both-posix.fxt both-posix.svg

examples/both/dune

@@ -0,0 +1,3 @@
+(executable
+  (name main)
+  (libraries eio_main))

examples/both/main.ml

@@ -0,0 +1,7 @@
+open Eio.Std
+
+let () =
+  Eio_main.run @@ fun _env ->
+  Fiber.both
+    (fun () -> for x = 1 to 3 do traceln "x = %d" x; Fiber.yield () done)
+    (fun () -> for y = 1 to 3 do traceln "y = %d" y; Fiber.yield () done)

lib_eio/core/debug.ml

@@ -8,6 +8,7 @@ let traceln_mutex = Mutex.create ()
 
 let default_traceln ?__POS__:pos fmt =
   let k go =
+    Trace.with_span "traceln" @@ fun () ->
     let b = Buffer.create 512 in
     let f = Format.formatter_of_buffer b in
     go f;

lib_eio/core/single_waiter.ml

@@ -25,3 +25,11 @@ let await t op id =
   in
   Trace.get id;
   x
+
+let await_protect t op id =
+  let x =
+    Suspend.enter_unchecked op @@ fun _ctx enqueue ->
+    t.wake <- (fun x -> t.wake <- ignore; enqueue x)
+  in
+  Trace.get id;
+  x

lib_eio/core/switch.ml

@@ -91,7 +91,7 @@ let rec await_idle t =
   (* Wait for fibers to finish: *)
   while t.fibers > 0 do
     Trace.try_get t.cancel.id;
-    Single_waiter.await t.waiter "Switch.await_idle" t.cancel.id
+    Single_waiter.await_protect t.waiter "Switch.await_idle" t.cancel.id
   done;
   (* Call on_release handlers: *)
   let queue = Lwt_dllist.create () in
@@ -102,15 +102,13 @@ let rec await_idle t =
     | None -> await_idle t
     | Some fn ->
       begin
-        try fn () with
+        try Cancel.protect fn with
         | ex -> fail t ex
       end;
       release ()
   in
   release ()
 
-let await_idle t = Cancel.protect (fun _ -> await_idle t)
-
 let maybe_raise_exs t =
   match t.exs with
   | None -> ()

lib_eio/unix/eio_unix.mli

@@ -50,9 +50,11 @@ val sleep : float -> unit
     without having to plumb {!Eio.Stdenv.mono_clock} through your code.
     It can also be used in programs that don't care about tracking determinism. *)
 
-val run_in_systhread : (unit -> 'a) -> 'a
+val run_in_systhread : ?label:string -> (unit -> 'a) -> 'a
 (** [run_in_systhread fn] runs the function [fn] in a newly created system thread (a {! Thread.t}).
-    This allows blocking calls to be made non-blocking. *)
+    This allows blocking calls to be made non-blocking.
+
+    @param label The operation name to use in trace output. *)
 
 val pipe : Switch.t -> source_ty r * sink_ty r
 (** [pipe sw] returns a connected pair of flows [src] and [sink]. Data written to [sink]

lib_eio/unix/net.ml

@@ -51,7 +51,7 @@ let getnameinfo (sockaddr : Eio.Net.Sockaddr.t) =
     | `Udp _ -> [Unix.NI_DGRAM]
   in
   let sockaddr = sockaddr_to_unix sockaddr in
-  Private.run_in_systhread (fun () ->
+  Private.run_in_systhread ~label:"getnameinfo" (fun () ->
     let Unix.{ni_hostname; ni_service} = Unix.getnameinfo sockaddr options in
     (ni_hostname, ni_service))
 

lib_eio/unix/private.ml

@@ -17,12 +17,7 @@ let pipe sw = Effect.perform (Pipe sw)
 module Rcfd = Rcfd
 module Fork_action = Fork_action
 
-let run_in_systhread fn =
-  let f fiber enqueue =
-    match Eio.Private.Fiber_context.get_error fiber with
-    | Some err -> enqueue (Error err)
-    | None ->
-      let _t : Thread.t = Thread.create (fun () -> enqueue (try Ok (fn ()) with exn -> Error exn)) () in
-      ()
-  in
-  Effect.perform (Eio.Private.Effects.Suspend f)
+let run_in_systhread ?(label="systhread") fn =
+  Eio.Private.Suspend.enter label @@ fun _ctx enqueue ->
+  let _t : Thread.t = Thread.create (fun () -> enqueue (try Ok (fn ()) with exn -> Error exn)) () in
+  ()

lib_eio/unix/rcfd.ml

@@ -97,6 +97,9 @@ let get t =
     put t;
     None
 
+let close_fd fd =
+  Eio.Private.Trace.with_span "close" (fun () -> Unix.close fd)
+
 (* Note: we could simplify this a bit by incrementing [t.ops], as [remove] does.
    However, that makes dscheck too slow. *)
 let close t =
@@ -105,14 +108,14 @@ let close t =
     (* Another caller closed [t] before us. *)
     false
   | Open fd as prev ->
-    let next = Closing (fun () -> Unix.close fd) in
+    let next = Closing (fun () -> close_fd fd) in
     if Atomic.compare_and_set t.fd prev next then (
       (* We just transitioned from [open] to [closing/users] or [closing/no-users].
          We are now the closer. *)
       if Atomic.get t.ops = 0 && Atomic.compare_and_set t.fd next fully_closed then (
         (* We were in [closing/no-users] and are now in [closing/closed].
            We own the FD (and our original callback will never be called). *)
-        Unix.close fd
+        close_fd fd
       ) else (
         (* The [next] callback remained installed and there is nothing left for us to do:
            - If [t.ops] was non-zero, another thread will eventually return it to zero and call our callback.

lib_eio_linux/low_level.ml

@@ -341,11 +341,11 @@ let lseek fd off cmd =
 
 let fsync fd =
   (* todo: https://github.com/ocaml-multicore/ocaml-uring/pull/103 *)
-  Eio_unix.run_in_systhread @@ fun () ->
+  Eio_unix.run_in_systhread ~label:"fsync" @@ fun () ->
   Fd.use_exn "fsync" fd Unix.fsync
 
 let ftruncate fd len =
-  Eio_unix.run_in_systhread @@ fun () ->
+  Eio_unix.run_in_systhread ~label:"ftruncate" @@ fun () ->
   Fd.use_exn "ftruncate" fd @@ fun fd ->
   Unix.LargeFile.ftruncate fd (Optint.Int63.to_int64 len)
 
@@ -479,7 +479,7 @@ let read_dir fd =
       let files = List.filter (function ".." | "." -> false | _ -> true) files in
       read_all (files @ acc) fd
   in
-  Eio_unix.run_in_systhread (fun () -> read_all [] fd)
+  Eio_unix.run_in_systhread ~label:"read_dir" (fun () -> read_all [] fd)
 
 (* https://www.iana.org/assignments/protocol-numbers/protocol-numbers.xhtml *)
 let getaddrinfo ~service node =
@@ -494,7 +494,7 @@ let getaddrinfo ~service node =
         | _ -> None)
     | _ -> None
   in
-  Eio_unix.run_in_systhread @@ fun () ->
+  Eio_unix.run_in_systhread ~label:"getaddrinfo" @@ fun () ->
   Unix.getaddrinfo node service []
   |> List.filter_map to_eio_sockaddr_t
 

lib_eio_linux/sched.ml

@@ -110,11 +110,14 @@ let enter op fn =
   Trace.suspend_fiber op;
   Effect.perform (Enter fn)
 
+let submit uring =
+  Trace.with_span "submit" (fun () -> Uring.submit uring)
+
 let rec enqueue_job t fn =
   match fn () with
   | Some _ as r -> r
   | None ->
-    if Uring.submit t.uring > 0 then enqueue_job t fn
+    if submit t.uring > 0 then enqueue_job t fn
     else None
 
 (* Cancellations always come from the same domain, so no need to send wake events here. *)
@@ -219,7 +222,7 @@ let rec schedule ({run_q; sleep_q; mem_q; uring; _} as st) : [`Exit_scheduler] =
         Lf_queue.push run_q IO;                   (* Re-inject IO job in the run queue *)
         handle_complete st ~runnable result
       | None ->
-        ignore (Uring.submit uring : int);
+        ignore (submit uring : int);
         let timeout =
           match next_due with
           | `Wait_until time ->

lib_eio_posix/low_level.ml

@@ -16,7 +16,7 @@ module Trace = Eio.Private.Trace
 module Fiber_context = Eio.Private.Fiber_context
 
 (* todo: keeping a pool of workers is probably faster *)
-let in_worker_thread = Eio_unix.run_in_systhread
+let in_worker_thread label = Eio_unix.run_in_systhread ~label
 
 let await_readable op fd =
   Fd.use_exn "await_readable" fd @@ fun fd ->
@@ -115,11 +115,11 @@ let getrandom { Cstruct.buffer; off; len } =
     else
       loop (n + eio_getrandom buffer (off + n) (len - n))
   in
-  in_worker_thread @@ fun () ->
+  in_worker_thread "getrandom" @@ fun () ->
   loop 0
 
 let realpath path =
-  in_worker_thread @@ fun () ->
+  in_worker_thread "realpath" @@ fun () ->
   Unix.realpath path
 
 let read_entries h =
@@ -132,7 +132,7 @@ let read_entries h =
   aux []
 
 let readdir path =
-  in_worker_thread @@ fun () ->
+  in_worker_thread "readdir" @@ fun () ->
   let h = Unix.opendir path in
   match read_entries h with
   | r -> Unix.closedir h; r
@@ -201,29 +201,29 @@ external eio_openat : Unix.file_descr -> string -> Open_flags.t -> int -> Unix.f
 let openat ?dirfd ~sw ~mode path flags =
   with_dirfd "openat" dirfd @@ fun dirfd ->
   Switch.check sw;
-  in_worker_thread (fun () -> eio_openat dirfd path Open_flags.(flags + cloexec + nonblock) mode)
+  in_worker_thread "openat" (fun () -> eio_openat dirfd path Open_flags.(flags + cloexec + nonblock) mode)
   |> Fd.of_unix ~sw ~blocking:false ~close_unix:true
 
 external eio_mkdirat : Unix.file_descr -> string -> Unix.file_perm -> unit = "caml_eio_posix_mkdirat"
 
 let mkdir ?dirfd ~mode path =
   with_dirfd "mkdirat" dirfd @@ fun dirfd ->
-  in_worker_thread @@ fun () ->
+  in_worker_thread "mkdir" @@ fun () ->
   eio_mkdirat dirfd path mode
 
 external eio_unlinkat : Unix.file_descr -> string -> bool -> unit = "caml_eio_posix_unlinkat"
 
 let unlink ?dirfd ~dir path =
   with_dirfd "unlink" dirfd @@ fun dirfd ->
-  in_worker_thread @@ fun () ->
+  in_worker_thread "unlink" @@ fun () ->
   eio_unlinkat dirfd path dir
 
 external eio_renameat : Unix.file_descr -> string -> Unix.file_descr -> string -> unit = "caml_eio_posix_renameat"
 
 let rename ?old_dir old_path ?new_dir new_path =
   with_dirfd "rename-old" old_dir @@ fun old_dir ->
   with_dirfd "rename-new" new_dir @@ fun new_dir ->
-  in_worker_thread @@ fun () ->
+  in_worker_thread "rename" @@ fun () ->
   eio_renameat old_dir old_path new_dir new_path
 
 type stat
@@ -236,7 +236,7 @@ let fstat ~buf fd =
   eio_fstat buf fd
 
 let fstatat ~buf ?dirfd ~follow path =
-  in_worker_thread @@ fun () ->
+  in_worker_thread "fstat" @@ fun () ->
   let flags = if follow then 0 else Config.at_symlink_nofollow in
   with_dirfd "fstatat" dirfd @@ fun dirfd ->
   eio_fstatat buf dirfd path flags
@@ -273,11 +273,11 @@ let lseek fd off cmd =
   |> Optint.Int63.of_int64
 
 let fsync fd =
-  Eio_unix.run_in_systhread @@ fun () ->
+  Eio_unix.run_in_systhread ~label:"fsync" @@ fun () ->
   Fd.use_exn "fsync" fd Unix.fsync
 
 let ftruncate fd len =
-  Eio_unix.run_in_systhread @@ fun () ->
+  Eio_unix.run_in_systhread ~label:"ftruncate" @@ fun () ->
   Fd.use_exn "ftruncate" fd @@ fun fd ->
   Unix.LargeFile.ftruncate fd (Optint.Int63.to_int64 len)
 

lib_eio_posix/net.ml

@@ -94,7 +94,7 @@ let getaddrinfo ~service node =
         | _ -> None)
     | _ -> None
   in
-  Err.run Eio_unix.run_in_systhread @@ fun () ->
+  Err.run (Eio_unix.run_in_systhread ~label:"getaddrinfo") @@ fun () ->
   let rec aux () =
     try
       Unix.getaddrinfo node service []

lib_eio_windows/net.ml

@@ -96,7 +96,7 @@ let getaddrinfo ~service node =
         | _ -> None)
     | _ -> None
   in
-  Err.run Eio_unix.run_in_systhread @@ fun () ->
+  Err.run (Eio_unix.run_in_systhread ~label:"getaddrinfo") @@ fun () ->
   let rec aux () =
     try
       Unix.getaddrinfo node service []