Provide when possible the thread name and gem name

gvl-tracing handles properly thread name for basic usage like:
```ruby
  Thread.new do
    Thread.current.name = "thread name
  end
```

But on more complicated with external libraries it is not able to
properly handles thread name.
Jean had a good idea in ivoanjo#9
about using `Thread.list`.

This commit does this:
- Store as list of json line, events we want to monitor
- Store `Thread.list` before stopping saving event related to the GVL
- Iterate of events store in json file and modify entries where we can
  find the name of the thread
- Go a little bit further when we can provide the gem name

This is a very naive approach and probably not super efficient. But this
is a first try.

examples/thread_name_with_extension.json

@@ -0,0 +1 @@
+[{"ph":"M","pid":81742,"tid":0,"name":"thread_name","args":{"name":null}},{"ph":"E","pid":81742,"tid":0,"ts":0.0},{"ph":"B","pid":81742,"tid":0,"ts":0.0,"name":"started_tracing"},{"ph":"M","pid":81742,"tid":1,"name":"thread_name","args":{"name":"worker-1 from concurrent-ruby"}},{"ph":"E","pid":81742,"tid":1,"ts":62.0},{"ph":"B","pid":81742,"tid":1,"ts":62.0,"name":"started"},{"ph":"E","pid":81742,"tid":1,"ts":65.0},{"ph":"B","pid":81742,"tid":1,"ts":65.0,"name":"wants_gvl"},{"ph":"M","pid":81742,"tid":2,"name":"thread_name","args":{"name":"worker-2 from concurrent-ruby"}},{"ph":"E","pid":81742,"tid":2,"ts":76.0},{"ph":"B","pid":81742,"tid":2,"ts":76.0,"name":"started"},{"ph":"E","pid":81742,"tid":2,"ts":78.0},{"ph":"B","pid":81742,"tid":2,"ts":78.0,"name":"wants_gvl"},{"ph":"M","pid":81742,"tid":3,"name":"thread_name","args":{"name":"worker-3 from concurrent-ruby"}},{"ph":"E","pid":81742,"tid":3,"ts":88.0},{"ph":"B","pid":81742,"tid":3,"ts":88.0,"name":"started"},{"ph":"E","pid":81742,"tid":3,"ts":89.0},{"ph":"B","pid":81742,"tid":3,"ts":89.0,"name":"wants_gvl"},{"ph":"M","pid":81742,"tid":4,"name":"thread_name","args":{"name":"worker-4 from concurrent-ruby"}},{"ph":"E","pid":81742,"tid":4,"ts":97.0},{"ph":"B","pid":81742,"tid":4,"ts":97.0,"name":"started"},{"ph":"E","pid":81742,"tid":4,"ts":98.0},{"ph":"B","pid":81742,"tid":4,"ts":98.0,"name":"wants_gvl"},{"ph":"M","pid":81742,"tid":5,"name":"thread_name","args":{"name":"worker-5 from concurrent-ruby"}},{"ph":"E","pid":81742,"tid":5,"ts":106.0},{"ph":"B","pid":81742,"tid":5,"ts":106.0,"name":"started"},{"ph":"E","pid":81742,"tid":5,"ts":107.0},{"ph":"B","pid":81742,"tid":5,"ts":107.0,"name":"wants_gvl"},{"ph":"E","pid":81742,"tid":0,"ts":146.0},{"ph":"B","pid":81742,"tid":0,"ts":146.0,"name":"stopped_tracing"}]

examples/thread_name_with_extension.rb

@@ -0,0 +1,18 @@
+# conrrent-ruby needs to be installed
+require "concurrent"
+require "gvl-tracing"
+
+def fib(n)
+  return n if n <= 1
+  fib(n - 1) + fib(n - 2)
+end
+
+GvlTracing.start("examples/thread_name_with_extension.json")
+pool = Concurrent::FixedThreadPool.new(5)
+
+40.times do
+  pool.post do
+    p fib(30)
+  end
+end
+GvlTracing.stop

ext/gvl_tracing_native_extension/extconf.rb

@@ -36,9 +36,9 @@
 have_header("pthread.h")
 have_func("pthread_getname_np", "pthread.h")
 have_func("pthread_threadid_np", "pthread.h")
-append_cflags('-Werror-implicit-function-declaration')
-append_cflags('-Wunused-parameter')
-append_cflags('-Wold-style-definition')
+append_cflags("-Werror-implicit-function-declaration")
+append_cflags("-Wunused-parameter")
+append_cflags("-Wold-style-definition")
 append_cflags("-Wall")
 append_cflags("-Wextra")
 

ext/gvl_tracing_native_extension/gvl_tracing.c

@@ -63,7 +63,7 @@ static VALUE gc_tracepoint = Qnil;
 void Init_gvl_tracing_native_extension(void) {
   rb_global_variable(&gc_tracepoint);
 
-  VALUE gvl_tracing_module = rb_define_module("GvlTracing");
+  VALUE gvl_tracing_module = rb_define_module("GvlTracingNativeExtension");
 
   rb_define_singleton_method(gvl_tracing_module, "start", tracing_start, 1);
   rb_define_singleton_method(gvl_tracing_module, "stop", tracing_stop, 0);
@@ -91,7 +91,7 @@ static inline void render_thread_metadata(void) {
   #endif
 
   fprintf(output_file,
-    "  {\"ph\": \"M\", \"pid\": %u, \"tid\": %u, \"name\": \"thread_name\", \"args\": {\"name\": \"%lu %s\"}},\n",
+    "  {\"ph\": \"M\", \"pid\": %u, \"tid\": %u, \"name\": \"thread_name\", \"args\": {\"name\": \"%lu %s\"}}\n",
     process_id, current_thread_serial, native_thread_id, native_thread_name_buffer
   );
 }
@@ -106,7 +106,6 @@ static VALUE tracing_start(VALUE _self, VALUE output_path) {
   started_tracing_at_microseconds = timestamp_microseconds();
   process_id = getpid();
 
-  fprintf(output_file, "[\n");
   render_event("started_tracing");
 
   current_hook = rb_internal_thread_add_event_hook(
@@ -143,7 +142,6 @@ static VALUE tracing_stop(VALUE _self) {
   gc_tracepoint = Qnil;
 
   render_event("stopped_tracing");
-  fprintf(output_file, "]\n");
 
   if (fclose(output_file) != 0) rb_syserr_fail(errno, "Failed to close GvlTracing output file");
 
@@ -158,7 +156,7 @@ static double timestamp_microseconds(void) {
   return (current_monotonic.tv_nsec / 1000.0) + (current_monotonic.tv_sec * 1000.0 * 1000.0);
 }
 
-// Render output using trace event format for perfetto:
+// Generate a list of trace event with format for perfetto that will be reformated lib/gvl_tracing:
 // https://chromium.googlesource.com/catapult/+/refs/heads/main/docs/trace-event-format.md
 static void render_event(const char *event_name) {
   // Event data
@@ -180,9 +178,9 @@ static void render_event(const char *event_name) {
 
   fprintf(output_file,
     // Finish previous duration
-    "  {\"ph\": \"E\", \"pid\": %u, \"tid\": %u, \"ts\": %f},\n" \
+    "{\"ph\": \"E\", \"pid\": %u, \"tid\": %u, \"ts\": %f}\n" \
     // Current event
-    "  {\"ph\": \"B\", \"pid\": %u, \"tid\": %u, \"ts\": %f, \"name\": \"%s\"},\n",
+    "{\"ph\": \"B\", \"pid\": %u, \"tid\": %u, \"ts\": %f, \"name\": \"%s\"}\n",
     // Args for first line
     process_id, thread_id, now_microseconds,
     // Args for second line

lib/gvl-tracing.rb

@@ -28,6 +28,50 @@
 require_relative "gvl_tracing/version"
 
 require "gvl_tracing_native_extension"
+require "json"
 
 module GvlTracing
+  class << self
+    @@path = "/tmp/gvl-tracing.json"
+
+    def start(file)
+      @@path = file
+      GvlTracingNativeExtension.start(@@path)
+    end
+
+    def stop
+      thread_list = Thread.list
+      GvlTracingNativeExtension.stop
+      set_thread_name(thread_list)
+    end
+
+    private
+
+    def set_thread_name(thread_list)
+      output_file = File.open(@@path)
+      output = output_file.read.split("\n").map do |event|
+        parse_event = JSON.parse(event)
+        thread_id = parse_event.dig("args", "name")
+
+        next(parse_event) unless thread_id
+
+        thread = thread_list.find { |t| t.native_thread_id.to_s == thread_id.strip }
+
+        next(parse_event) unless thread
+
+        parse_event["args"]["name"] = thread_label(thread)
+        parse_event
+      end
+      File.write(@@path, output.to_json)
+    end
+
+    REGEX = /lib(?!.*lib)\/([a-zA-Z-]+)/
+    def thread_label(thread)
+      lib_name = thread.to_s.match(REGEX)
+
+      return thread.name if lib_name.nil?
+
+      "#{thread.name} from #{lib_name[1]}"
+    end
+  end
 end