GVL Instrumentation: pass thread->self as part of event data

Context: https://github.com/ivoanjo/gvl-tracing/pull/4

Some hooks may want to collect data on a per thread basis.
Right now the only way to identify the concerned thread is to
use `rb_nativethread_self()` or similar, but even then because
of the thread cache or MaNy, two distinct Ruby threads may report
the same native thread id.

By passing `thread->self`, hooks can use it as a key to store
the metadata.

NB: Most hooks are executed outside the GVL, so such data collection
need to use a thread-safe data-structure, and shouldn't use the
reference in other ways from inside the hook.

They must also either pin that value or handle compaction.

1 files changed, 7 insertions, 0 deletions

diff --git a/test/-ext-/thread/test_instrumentation_api.rb b/test/-ext-/thread/test_instrumentation_api.rb
index dd620e7380..208d11de85 100644
--- a/test/-ext-/thread/test_instrumentation_api.rb
+++ b/test/-ext-/thread/test_instrumentation_api.rb
@@ -22,6 +22,7 @@ class TestThreadInstrumentation < Test::Unit::TestCase
   def teardown
     return if /mswin|mingw|bccwin/ =~ RUBY_PLATFORM
     Bug::ThreadInstrumentation::unregister_callback
+    Bug::ThreadInstrumentation.last_spawned_thread = nil
   end
 
   THREADS_COUNT = 3
@@ -68,6 +69,12 @@ class TestThreadInstrumentation < Test::Unit::TestCase
     assert Bug::ThreadInstrumentation::register_and_unregister_callbacks
   end
 
+  def test_thread_instrumentation_event_data
+    assert_nil Bug::ThreadInstrumentation.last_spawned_thread
+    thr = Thread.new{ }.join
+    assert_same thr, Bug::ThreadInstrumentation.last_spawned_thread
+  end
+
   private
 
   def fib(n = 20)