Validate Tracer is safe for concurrent calls

[codeboten]

Part of the work required for GA is to validate that the Tracer is safe for concurrent calls. Ideally this issue would be resolved by adding tests to validate this.

[codeboten]

Having reviewed the methods available in the Tracer API and their implementations in the SDK:

• start_span: threadsafe
• use_span: uses the context api which is threadlocal or contextvars for storage. any calls to the span API are either atomic, or are using a lock where needed ie. end here:

  opentelemetry-python/opentelemetry-sdk/src/opentelemetry/sdk/trace/__init__.py

  Lines 623 to 624 in 2d873e5

  	def end(self, end_time: Optional[int] = None) -> None:
  	with self._lock:

• start_as_current_span: uses start_span and use_span which have both been reviewed