It turns out that under some circumstances we end up clearing the
pointee of `current` but not the pointer. Thus when we select the next
slot we can end up reusing the same slot, making it its own parent.
We forcefull break these cycles by enforcing that `current` should
never be returned and be set as its own parent.
Changelog-None
Trace spans form a tree, but we don't actually check that the
structure doesn't break. Breakage can for example come if we use the
same key accidentally, making a new span its own ancestor.
We have the space in memory set aside anyway, so let's just copy the
`trace_id` into the span itself, rather than resolving the `root` at
time of emission.
After adding the DB query instrumentation we ran into a couple of
issues, with spans not being resumed correctly, and it was rather hard
to identify the problem. This adds debug statements so we can trace
the tracing (traception if you will).
Changelog-None
The integration with opentelemetry was sub-optimal: it was generating
jaeger-style traces, with short traceIds and we were considering the
entire lifetime as a single trace. This PR changes that to a trace for
startup and then a trace for any event that doesn't already have a
parent.
We also allow using the `CLN_TRACEPARENT` envvar to attach the startup
to a remote / external trace, potentially by whatever started the main
process. This is useful to see the startup trace in the wider context
of whatever tooling is built around it.
Changelog-Added: tracing: It is now possible to inject a parent for the startup trace by setting the `CLN_TRACEPARENT` envvar
