erts: Fix seq_trace to not clear token for system messages

A lot of erts internal messages used behind APIs to create
non-blocking calls, e.g. port_command, would cause the seq_trace
token to be cleared from the caller when it should not.
This commit fixes that and adds asserts that makes sure
that all messages sent have to correct token set.

Fixes: ERL-602

1 files changed, 18 insertions, 0 deletions

diff --git a/lib/kernel/test/seq_trace_SUITE.erl b/lib/kernel/test/seq_trace_SUITE.erl
index ceb4e9cc49..cf4bf11328 100644
--- a/lib/kernel/test/seq_trace_SUITE.erl
+++ b/lib/kernel/test/seq_trace_SUITE.erl
@@ -783,6 +783,24 @@ do_shrink(N) ->
     erlang:garbage_collect(),
     do_shrink(N-1).
 
+%% Test that messages from a port does not clear the token
+port_clean_token(Config) when is_list(Config) ->
+    seq_trace:reset_trace(),
+    Label = make_ref(),
+    seq_trace:set_token(label, Label),
+    {label,Label} = seq_trace:get_token(label),
+
+    %% Create a port and get messages from it
+    %% We use os:cmd as a convenience as it does
+    %% open_port, port_command, port_close and receives replies.
+    %% Maybe it is not ideal to rely on the internal implementation
+    %% of os:cmd but it will have to do.
+    os:cmd("ls"),
+
+    %% Make sure that the seq_trace token is still there
+    {label,Label} = seq_trace:get_token(label),
+
+    ok.
 
 
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%