* Update License header for all source files
- Add Apache 2.0 header to source files that did not have one.
- Update all existing headers dated to 2019 to be 2020
- Remove comma from License header to comply with the Apache 2.0
guidelines.
* Update Copyright notice
Use the standard Copyright notices outlined by the
[CNCF](https://github.com/cncf/foundation/blob/master/copyright-notices.md#copyright-notices)
When during determining a parent for a new span, we find out that
there is a current span in the context, we are putting a remote span
context into links as an ignored on demand. A problem with this
approach is that the remote span context will end up in links of every
descendant span. Another problem is that jaeger exporter currently
treats all links as span contexts with a "child of" relationship and
that likely confuses the jaeger visualization.
This PR removes the non-compliant ChildOf and FollowsFrom interfaces
and the Relation type, which were inherited from OpenTracing via the
initial prototype. Instead allow adding a span context to the go
context as a remote span context and use a simple algorithm for
figuring out an actual parent of the new span, which was proposed for
the OpenTelemetry specification.
Also add a way to ignore current span and remote span context in go
context, so we can force the tracer to create a new root span - a span
with a new trace ID.
That required some moderate changes in the opentracing bridge - first
reference with ChildOfRef reference type becomes a local parent, the
rest become links. This also fixes links handling in the meantime. The
downside of the approach proposed here is that we can only set the
remote parent when creating a span through the opentracing API.
Co-authored-by: Joshua MacDonald <jmacd@users.noreply.github.com>
