Split tracer inner segment sender and receiver into traits.

[jmjoy]

So users can customize the channel inside the tracer, such as using ipc channel.

[codecov-commenter]

Codecov Report

Merging #37 (cc9ddb7) into master (6232828) will increase coverage by 4.51%.
The diff coverage is 54.54%.

@@            Coverage Diff             @@
##           master      #37      +/-   ##
==========================================
+ Coverage   38.08%   42.59%   +4.51%     
==========================================
  Files          13       14       +1     
  Lines         323      385      +62     
==========================================
+ Hits          123      164      +41     
- Misses        200      221      +21     

Impacted Files	Coverage Δ
src/context/tracer.rs	55.20% <51.92%> (+16.31%)	⬆️
src/reporter/log.rs	21.05% <100.00%> (ø)
src/reporter/mod.rs	100.00% <100.00%> (ø)

Help us with your feedback. Take ten seconds to tell us how you rate us.

[wu-sheng]

What is ipc channel? Could you provide a case about how to use this?

[jmjoy]

What is ipc channel? Could you provide a case about how to use this?

The ipc channel can transmit data across processes, which is need in some multi-process architecture services (such as nginx and php-fpm), like in https://github.com/jmjoy/php-skywalking-agent/blob/705d08e716f80a3f0cad4c2efd211709bf384adb/src/module.rs#L73.

[wu-sheng]

OK, so, you want to propagate collected segments or tracing context, or both?

[jmjoy]

OK, so, you want to propagate collected segments or tracing context, or both?

Only segments.

[wu-sheng]

So, generally, you just want one process to report segments? Because this has better perf.?

[jmjoy]

So, generally, you just want one process to report segments? Because this has better perf.?

There is one manager process to report segments to skywalking server via grpc, and multi worker process to handle request, generate segments and transmit to manager process via ipc channel.