Restore default SIGINT behavior after taking snapshot

This feels like a hack, but it works for now pending discussion with
async devs.

Signed-off-by: Tudor Brindus <[email protected]>

Author: Xyene

src/trace.ml

@@ -454,16 +454,14 @@ module Make_commands (Backend : Backend_intf.S) = struct
     Ptrace.resume pid;
     (* Forward ^C to the child, unless it has already exited. *)
     let exited_ivar = Ivar.create () in
-    Async_unix.Signal.handle
-      ~stop:(Ivar.read exited_ivar)
-      Async_unix.Signal.terminating
-      ~f:(fun signal ->
-        try
-          UnixLabels.kill ~pid:(Pid.to_int pid) ~signal:(Signal_unix.to_system_int signal)
-        with
-        | Core_unix.Unix_error (_, (_ : string), (_ : string)) ->
-          (* We raced, but it's OK because the child still exited. *)
-          ());
+    let stop = Ivar.read exited_ivar in
+    Async_unix.Signal.handle ~stop Async_unix.Signal.terminating ~f:(fun signal ->
+      try
+        UnixLabels.kill ~pid:(Pid.to_int pid) ~signal:(Signal_unix.to_system_int signal)
+      with
+      | Core_unix.Unix_error (_, (_ : string), (_ : string)) ->
+        (* We raced, but it's OK because the child still exited. *)
+        ());
     (* [Monitor.try_with] because [waitpid] raises if perf died before we got here. *)
     let%bind.Deferred (waitpid_result : (Core_unix.Exit_or_signal.t, exn) result) =
       Monitor.try_with (fun () -> Async_unix.Unix.waitpid pid)
@@ -478,6 +476,12 @@ module Make_commands (Backend : Backend_intf.S) = struct
          error);
     (* This is still a little racey, but it's the best we can do without pidfds. *)
     Ivar.fill exited_ivar ();
+    (* CR-someday tbrindus: [~stop] doesn't make [Async_unix.Signal.handle] restore signal
+       handlers to their default state, so the decoding step won't be ^C-able. Restore
+       SIGINT's handler here. Ideally we'd restore all [terminating] handlers to their
+       default behavior, but I'm not convinced that doesn't break Async and SIGINT is all
+       we really need. *)
+    Deferred.upon stop (fun () -> Core.Signal.Expert.set Signal.int `Default);
     let%bind () = detach attachment in
     return pid
   ;;
@@ -497,6 +501,7 @@ module Make_commands (Backend : Backend_intf.S) = struct
     Async_unix.Signal.handle ~stop [ Signal.int ] ~f:(fun (_ : Signal.t) ->
       Core.eprintf "[ Got signal, detaching... ]\n%!";
       Ivar.fill_if_empty done_ivar ());
+    Deferred.upon stop (fun () -> Core.Signal.Expert.set Signal.int `Default);
     Core.eprintf "[ Attached. Press Ctrl-C to stop recording. ]\n%!";
     let%bind () = stop in
     detach attachment