Fixes block form of #start

* Because the ensure calls `_stop` instead of `stop`, the block form produces invalid json

* Perfetto is pretty permissive about this and still accepts the file - but other tools break and JSON parsing is broken

* Also adds first specs for the project, covering a few different scenarios 🎉

.gitignore

@@ -12,4 +12,5 @@ gems.locked
 *.bundle
 example*json
 thread_name_with_extension.json
-.DS_Store
+.DS_Store
+.rspec_status

.ruby-version

@@ -1 +1 @@
-ruby-3.2.0
+ruby-3.2.2

README.adoc

@@ -76,7 +76,9 @@ This way you can actually link from your dashboards and similar pages directly t
 
 == Development
 
-To install this gem onto your local machine, run `bundle exec rake install`. To release a new version, update the version number in `version.rb`, and then run `bundle exec rake release`, which will create a git tag for the version, push git commits and the created tag, and push the `.gem` file to https://rubygems.org[rubygems.org].
+To install this gem onto your local machine, run `bundle exec rake install`. To release a new version, update the version number in `version.rb`, and then run `bundle exec rake release`, which will create a git tag for the version, push git commits and the created tag, and push the `.gem` file to https://rubygems.org[rubygems.org]. To run specs, run `bundle exec rake spec`.
+
+To run all actions (build the extension, check linting, and run specs), run `bundle exec rake`.
 
 == Contributing
 

Rakefile

@@ -28,7 +28,9 @@
 require "bundler/gem_tasks"
 require "standard/rake"
 require "rake/extensiontask"
+require "rspec/core/rake_task"
 
 Rake::ExtensionTask.new("gvl_tracing_native_extension")
+RSpec::Core::RakeTask.new(:spec)
 
-task default: [:compile, :"standard:fix"]
+task default: [:compile, :"standard:fix", :spec]

gems.rb

@@ -7,5 +7,7 @@
 gem "rake", "~> 13.0"
 gem "rake-compiler", "~> 1.2"
 gem "pry"
+gem "pry-byebug"
+gem "rspec"
 gem "standard", "~> 1.12"
 gem "concurrent-ruby"

lib/gvl-tracing.rb

@@ -43,7 +43,7 @@ def start(file)
       begin
         yield
       ensure
-        _stop
+        stop
       end
     end
 

spec/gvl_tracing_spec.rb

@@ -0,0 +1,69 @@
+# frozen_string_literal: true
+
+require "spec_helper"
+require "json"
+require "net/http"
+require "perfetto_trace"
+
+RSpec.describe GvlTracing do
+  let(:trace_path) { "tmp/gvl.json" }
+
+  it "has a version number" do
+    expect(GvlTracing::VERSION).not_to be nil
+  end
+
+  describe "#start" do
+    it "fails if already started" do
+      expect {
+        GvlTracing.start(trace_path) { GvlTracing.start(trace_path) }
+      }.to raise_error(/Already started/)
+    end
+
+    describe "with a block" do
+      before do
+        GvlTracing.start(trace_path) {}
+      end
+
+      it "stops tracing after the block" do
+        expect(File.exist?(trace_path)).to be_truthy
+      end
+
+      it "creates valid json" do
+        expect { JSON.parse(File.read(trace_path)) }.to_not raise_error
+      end
+    end
+  end
+
+  describe "#stop" do
+    it "fails if not started" do
+      expect { GvlTracing.stop }.to raise_error(/Tracing not running/)
+    end
+
+    it "closes out the json" do
+      GvlTracing.start(trace_path)
+      expect { JSON.parse(File.read(trace_path)) }.to raise_error(JSON::ParserError)
+
+      GvlTracing.stop
+      expect(JSON.parse(File.read(trace_path))).to be_an(Array)
+    end
+  end
+
+  describe "order of events" do
+    it "writes events in valid order" do
+      GvlTracing.start(trace_path) do
+        Thread.new {}.join
+        Thread.new {}.join
+      end
+
+      trace = PerfettoTrace.new(trace_path)
+      threads = trace.non_main_threads
+
+      threads.each do |thread|
+        events = trace.events_by_thread[thread.tid]
+        names = events.map(&:name).reject { |n| !n }
+
+        expect(names).to match_array(%w[thread_name running wants_gvl waiting died])
+      end
+    end
+  end
+end

spec/perfetto_trace.rb

@@ -0,0 +1,51 @@
+# frozen_string_literal: true
+
+class PerfettoTrace
+  def initialize(file_path)
+    @trace = JSON.parse(File.read(file_path))
+  end
+
+  def threads
+    @trace
+      .select { |j| j["ph"] == "M" && j["name"] == "thread_name" }
+      .uniq { |j| j["args"]["tid"] }
+      .map { |j| Row.new(j) }
+  end
+
+  def non_main_threads
+    threads.select { |t| t.thread_name != "Main Thread" }
+  end
+
+  def events_by_thread
+    @trace
+      .group_by { |j| j["tid"] }
+      .map { |tid, events| [tid, events.map { |j| Row.new(j) }] }
+      .to_h
+  end
+
+  class Row
+    def initialize(row)
+      @row = row
+    end
+
+    def meta? = ph == "M"
+
+    def phase_begin? = ph == "B"
+
+    def phase_end? = ph == "E"
+
+    def phase = @row["ph"]
+
+    def pid = @row["pid"]
+
+    def tid = @row["tid"]
+
+    def ts = @row["ts"]
+
+    def name = @row["name"]
+
+    def args = @row["args"]
+
+    def thread_name = @row.dig("args", "name")
+  end
+end

spec/spec_helper.rb

@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+
+require "bundler/setup"
+require "gvl-tracing"
+require "pry"
+require "pry-byebug"
+
+RSpec.configure do |config|
+  config.example_status_persistence_file_path = ".rspec_status"
+
+  config.disable_monkey_patching!
+
+  config.expect_with :rspec do |c|
+    c.syntax = :expect
+  end
+end