Add optional span param to end_span

[matheussilvasantos]

What does this pull request do?

Add optional span param to end_span

Why is it important?

When using the gem in asynchronous systems, multiple spans will be created in parallel, and they aren't going to finish in the same order they were created. Therefore, to have spans with the correct duration, we need to pass the span we want to finish - in this case, it's the developer responsibility to hold the span created and pass it to end_span.

Usage example:

require "eventmachine"
require "em-http"
require "elastic_apm"

puts "Starting..."

ElasticAPM.start

EM.run do
  ElasticAPM.start_transaction("Transaction")

  count = 0

  ["https://example.com", "https://example.org"].each do |url|
    span = ElasticAPM.start_span("GET #{url}")

    http = EventMachine::HttpRequest.new(url).get

    http.errback do
      ElasticAPM.end_span(span)
      count += 1
    end

    http.callback do
      ElasticAPM.end_span(span)
      count += 1
    end
  end

  timer = EventMachine::PeriodicTimer.new(1) do
    if count == 2
      ElasticAPM.end_transaction
      puts "Stopping..."
      EM.add_timer(5) do
        ElasticAPM.stop
        EM.stop
      end
      timer.cancel
    end
  end
end

Checklist

• I have signed the Contributor License Agreement.
• My code follows the style guidelines of this project (See .rubocop.yml)
• I have rebased my changes on top of the latest master branch
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have made corresponding changes to the documentation
• I have updated CHANGELOG.asciidoc
• I have updated supported-technologies.asciidoc
• Added an API method or config option? Document in which version this will be introduced
  (I'm not sure on this one)

[ghost]

💚 Build Succeeded

the below badges are clickable and redirect to their specific view in the CI or DOCS

Expand to view the summary

Build stats

• Start Time: 2021-07-29T12:49:04.704+0000

• Duration: 24 min 2 sec

• Commit: cbd8b40

Test stats 🧪

Test	Results
Failed	0
Passed	46153
Skipped	84
Total	46237

Trends 🧪

[mikker]

This is wonderful! Great addition. I don't remember anyone else using the agent with EventMachine so keep the fixes and additions coming as you encounter them ❤️

[mikker]

jenkins, run the tests

[mikker]

jenkins, run the tests

[estolfo]

Thanks @matheussilvasantos!