Is Python multiprocessing supported?

Hi,

I've been trying to get AWS X-Ray working in my Python application where I spin up separate Python processes via Pool() and apply_async. I'm passing in the segment from .get_trace_entity and setting it in the child process, but I'm still getting exceptions that seem to suggest the segment isn't getting passed properly, e.g.:
```
2020-07-08 15:57:54,703] {{taskinstance.py:1088}} ERROR - 'Segment' object has no attribute 'sampled'
multiprocessing.pool.RemoteTraceback:
"""
Traceback (most recent call last):
File "/usr/local/lib/python3.7/multiprocessing/pool.py", line 121, in worker
result = (True, func(*args, **kwds))
File "/usr/local/lib/python3.7/site-packages/xxxx-0.1-py3.7.egg/xxxx/elt/extract/kinesis_handler.py", line 52, in push_to_kinesis
xray_recorder.begin_subsegment('push_to_kinesis')
File "/usr/local/lib/python3.7/site-packages/aws_xray_sdk/core/recorder.py", line 297, in begin_subsegment
if not segment.sampled:
AttributeError: 'Segment' object has no attribute 'sampled'
"""
```

Does X-Ray support tracking segments through separate processes, or am I just doing something wrong? I noticed in the documentation it only mentions ThreadPoolExecutor, and I know sharing state with separate processes can be a bit fiddly due to pickling.

Thanks in advance!

Beginne mit dem Dokumentationsabschnitt, in dem ThreadPoolExecutor und die Recorder-Einstiegspunkte get_trace_entity und begin_subsegment erwähnt werden. Reproduziere den im Issue beschriebenen Fall mit Pool() und apply_async und ermittle anschließend, ob Tracing in separaten Prozessen unterstützt wird oder welches Verhalten dokumentiert werden muss; abgeschlossen ist die Aufgabe, wenn es für diesen Anwendungsfall eine klare, getestete Antwort gibt.

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