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, 3 insertions, 1 deletions

diff --git a/include/ruby/thread.h b/include/ruby/thread.h
index d6a543af91..f6eea65b70 100644
--- a/include/ruby/thread.h
+++ b/include/ruby/thread.h
@@ -227,7 +227,9 @@ void *rb_nogvl(void *(*func)(void *), void *data1,
 
 #define RUBY_INTERNAL_THREAD_EVENT_MASK       0xff /** All Thread events */
 
-typedef void rb_internal_thread_event_data_t; // for future extension.
+typedef struct rb_internal_thread_event_data {
+   VALUE thread;
+} rb_internal_thread_event_data_t;
 
 typedef void (*rb_internal_thread_event_callback)(rb_event_flag_t event,
               const rb_internal_thread_event_data_t *event_data,