[Feature]: SimpleSpanProcessor to be consistent with SimpleLogRecordProcessor

[cijothomas]

Related Problems?

No response

Describe the solution you'd like:

#1308 modified SimpleLogRecordProcessor to simply take a Mutex protected call to Exporter.
Proposing to make the similar change to SimpleSpanProcessor, effectively reversing #502.

We'll get to eliminate the crossbeam-channel by doing this, and also ensures there is more consistency between signals.

Considered Alternatives

No response

Additional Context

No response

[jtescher]

This may simplify things, but we should check the overall throughput to make sure it's still acceptable given our performance focus (e.g. if an exporter has an average latency of ~1 second)

[cijothomas]

I don't think the perf would be good here (and will directly be affected by how slow the exporter is!). For performance scenarios - there is BatchProcessors to the rescue, so my main point was - we should not worry about perf for SimpleProcessor, which should only be used for testing/learning purposes!

[cijothomas]

Any further comments/objections to do this?

[lalitb]

One of the concerns I believe was users needing performance in hot-path without depending on the external runtime. This should be resolved with #1506.