seq_trace: Inherit trace token on spawn

Trace tokens can be lost when a process delegates message sending
to a child process, which is pretty surprising and limits the
usefulness of seq tracing. One example of this is gen_statem:call/4
which uses a child process to implement timeouts without the risk
of a late message arriving to the caller.

This commit attempts to remedy this by propagating the trace token
to spawned processes, and adds optional tracing for process
spawning as well.

1 files changed, 1 insertions, 1 deletions

diff --git a/erts/emulator/beam/bif.c b/erts/emulator/beam/bif.c
index c102ddbee6..21352ec844 100644
--- a/erts/emulator/beam/bif.c
+++ b/erts/emulator/beam/bif.c
@@ -1987,7 +1987,7 @@ do_send(Process *p, Eterm to, Eterm msg, Eterm return_term, Eterm *refp,
                 trace_send(p, portid, msg);
 
             if (have_seqtrace(SEQ_TRACE_TOKEN(p))) {
-                seq_trace_update_send(p);
+                seq_trace_update_serial(p);
                 seq_trace_output(SEQ_TRACE_TOKEN(p), msg,
                                  SEQ_TRACE_SEND, portid, p);
             }