Add __getnewargs__ to SpanContext class

[rickychu]

Description

SpanContext does not support pickle due to missing getnewargs function. Add function to SpanContext.

Fixes # (issue)
#1375

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

• Tor

Checklist:

• Followed the style guidelines of this project
• Changelogs have been updated
• Unit tests have been added
• Documentation has been updated

[ocelotl]

Interesting. Just out of curiosity, what was the use case that made you open this PR, @rickychu?

[rickychu]

Interesting. Just out of curiosity, what was the use case that made you open this PR, @rickychu?

I have a multiprocessing script where the pools need to continue with the span context so it has to be pickled.

def processing_data():
    ...
    with tracer.start_as_current_span("processing_data") as span:
        work_items = get_all_work_items_to_process()

    ...
    with multiprocessing.Pool(cpu_limit) as pool:
        pool.map(partial(worker, context=span.get_current_context()), work_items)

Error:
TypeError: new() missing 2 required positional arguments: 'span_id' and 'is_remote'

It works in 0.13b0 with span.get_context()

[toumorokoshi]

LGTM, thanks!

[codeboten]

Thanks for the PR!