From 9f2b0ca46bc813476ac821792b0bc53e4cd74c50 Mon Sep 17 00:00:00 2001
From: Ulf Wiger <ulf@wiger.net>
Date: Fri, 5 Jun 2026 20:54:43 +0200
Subject: [PATCH] Spawned processes inherit the parent's flow identity

---
 src/gm_ctflow.erl | 23 ++++++++++++++++++-----
 1 file changed, 18 insertions(+), 5 deletions(-)

diff --git a/src/gm_ctflow.erl b/src/gm_ctflow.erl
index a010875..d1fdf0d 100644
--- a/src/gm_ctflow.erl
+++ b/src/gm_ctflow.erl
@@ -7,6 +7,7 @@
         ]).
 
 -export([ note_flow/1
+        , get_flow/0
         , ct_log/2          %% ct_log(Fmt, Args)
         , ct_log/3          %% ct_log(Flow, Fmt, Args)
         , timestamp/0 ]).
@@ -44,9 +45,14 @@ get(Key, Default) ->
 erase(Key) ->
     gm_ctflow_state:erase(Key).
 
-
+-spec note_flow(flow()) -> 'ok'.
 note_flow(Flow) ->
-    erlang:put({?MODULE, flow}, Flow).
+    erlang:put({?MODULE, flow}, Flow),
+    ok.
+
+-spec get_flow() -> flow() | 'undefined'.
+get_flow() ->
+    erlang:get({?MODULE, flow}).
 
 ct_log(Fmt, Args) ->
     ct_log(erlang:get({?MODULE, flow}), Fmt, Args).
@@ -136,13 +142,20 @@ timestamp() ->
                                 [Year,Month,Day,Hour,Min,Sec,MilliSec])).
 
 spawn(F) ->
+    Flow = get_flow(),
     proc_lib:spawn(fun() ->
+                           maybe_inherit_flow(Flow),
                            ct_util:mark_process(),
                            F()
                    end).
 
 spawn_opt(F, Opts) ->
+    Flow = get_flow(),
     proc_lib:spawn_opt(fun() ->
-                                ct_util:mark_process(),
-                                F()
-                        end, Opts).
+                               maybe_inherit_flow(Flow),
+                               ct_util:mark_process(),
+                               F()
+                       end, Opts).
+
+maybe_inherit_flow(undefined) -> ok;
+maybe_inherit_flow(Flow)      -> note_flow(Flow).