From c3fa0fdf8c333955de80167972bf83b22c6564c0 Mon Sep 17 00:00:00 2001
From: Matt Valentine-House <matt@eightbitraptor.com>
Date: Mon, 24 Jan 2022 16:05:23 +0000
Subject: [PATCH] [wip] Allow callbacks to be registered for GVL related events

---
 .../gvl/call_without_gvl/call_without_gvl.c   | 22 +++++++++++++
 include/ruby/thread.h                         |  1 +
 include/ruby/thread_native.h                  |  7 +++++
 test/-ext-/gvl/test_last_thread.rb            |  7 +++++
 thread_pthread.c                              | 31 +++++++++++++++++++
 thread_pthread.h                              | 11 +++++++
 6 files changed, 79 insertions(+)

diff --git a/ext/-test-/gvl/call_without_gvl/call_without_gvl.c b/ext/-test-/gvl/call_without_gvl/call_without_gvl.c
index 233635421b816f..e845914782d8ae 100644
--- a/ext/-test-/gvl/call_without_gvl/call_without_gvl.c
+++ b/ext/-test-/gvl/call_without_gvl/call_without_gvl.c
@@ -1,5 +1,6 @@
 #include "ruby/ruby.h"
 #include "ruby/thread.h"
+#include "ruby/thread_native.h"
 
 static void*
 native_sleep_callback(void *data)
@@ -68,6 +69,25 @@ thread_ubf_async_safe(VALUE thread, VALUE notify_fd)
     return Qnil;
 }
 
+void
+ex_callback(uint32_t e, struct gvl_hook_event_args args) {
+    fprintf(stderr, "calling callback\n");
+}
+
+static VALUE
+thread_register_gvl_callback(VALUE thread) {
+    rb_gvl_event_new(*ex_callback, 0x12);
+
+
+    return Qnil;
+}
+
+static VALUE
+thread_call_gvl_callback(VALUE thread) {
+    rb_gvl_execute_hooks(0x12); 
+    return Qnil;
+}
+
 void
 Init_call_without_gvl(void)
 {
@@ -75,4 +95,6 @@ Init_call_without_gvl(void)
     VALUE klass = rb_define_module_under(mBug, "Thread");
     rb_define_singleton_method(klass, "runnable_sleep", thread_runnable_sleep, 1);
     rb_define_singleton_method(klass, "ubf_async_safe", thread_ubf_async_safe, 1);
+    rb_define_singleton_method(klass, "register_callback", thread_register_gvl_callback, 0);
+    rb_define_singleton_method(klass, "call_callbacks", thread_call_gvl_callback, 0);
 }
diff --git a/include/ruby/thread.h b/include/ruby/thread.h
index 18c792b3861ccc..cc0ceeffc4cc09 100644
--- a/include/ruby/thread.h
+++ b/include/ruby/thread.h
@@ -190,6 +190,7 @@ void *rb_nogvl(void *(*func)(void *), void *data1,
  */
 #define RUBY_CALL_WO_GVL_FLAG_SKIP_CHECK_INTS_
 
+
 RBIMPL_SYMBOL_EXPORT_END()
 
 #endif /* RUBY_THREAD_H */
diff --git a/include/ruby/thread_native.h b/include/ruby/thread_native.h
index c23b15e133a81f..ae1df02343f7ee 100644
--- a/include/ruby/thread_native.h
+++ b/include/ruby/thread_native.h
@@ -201,5 +201,12 @@ void rb_native_cond_initialize(rb_nativethread_cond_t *cond);
  */
 void rb_native_cond_destroy(rb_nativethread_cond_t *cond);
 
+#include <stdint.h>
+struct gvl_hook_event_args {
+    //
+};
+typedef void (*rb_gvl_callback)(uint32_t event, struct gvl_hook_event_args args);
+void rb_gvl_event_new(void *callback, uint32_t event);
+void rb_gvl_execute_hooks(uint32_t event);
 RBIMPL_SYMBOL_EXPORT_END()
 #endif
diff --git a/test/-ext-/gvl/test_last_thread.rb b/test/-ext-/gvl/test_last_thread.rb
index f1bebafeea942e..791e13834d581a 100644
--- a/test/-ext-/gvl/test_last_thread.rb
+++ b/test/-ext-/gvl/test_last_thread.rb
@@ -18,5 +18,12 @@ def test_last_thread
       assert_in_delta(1.0, t, 0.16)
     end;
   end
+
+  def test_gvl_instrumentation
+    require '-test-/gvl/call_without_gvl'
+    Bug::Thread::register_callback
+
+    Bug::Thread::call_callbacks
+  end
 end
 
diff --git a/thread_pthread.c b/thread_pthread.c
index 55289de73a3be4..5665afbe727679 100644
--- a/thread_pthread.c
+++ b/thread_pthread.c
@@ -101,6 +101,37 @@
 #  endif
 #endif
 
+static gvl_hook_t * rb_gvl_hooks = NULL;
+
+void
+rb_gvl_event_new(void *callback, uint32_t event) {
+    gvl_hook_t *hook = ALLOC_N(gvl_hook_t, 1);
+    hook->callback = callback;
+    hook->event = event;
+
+    if(!rb_gvl_hooks) {
+        rb_gvl_hooks = hook;
+    } else {
+        hook->next = rb_gvl_hooks;
+        rb_gvl_hooks = hook;
+    }
+}
+
+void
+rb_gvl_execute_hooks(uint32_t event) {
+    if (!rb_gvl_hooks) {
+        return;
+    }
+    gvl_hook_t *h = rb_gvl_hooks;
+    struct gvl_hook_event_args args = {};
+
+    do {
+        if (h->event & event) {
+            (*h->callback)(event, args);
+        }
+    } while((h = h->next));
+}
+
 enum rtimer_state {
     /* alive, after timer_create: */
     RTIMER_DISARM,
diff --git a/thread_pthread.h b/thread_pthread.h
index 2ac354046c010b..240c8d9fe453e6 100644
--- a/thread_pthread.h
+++ b/thread_pthread.h
@@ -69,6 +69,17 @@ typedef struct rb_global_vm_lock_struct {
     int wait_yield;
 } rb_global_vm_lock_t;
 
+#include <stdint.h>
+
+// TODO: this is going to be the same on Windows so move it somewhere sensible
+typedef struct gvl_hook {
+    rb_gvl_callback callback;
+    uint32_t event;
+
+    struct gvl_hook *next;
+} gvl_hook_t;
+
+#include "ruby/internal/memory.h"
 
 #if __STDC_VERSION__ >= 201112
   #define RB_THREAD_LOCAL_SPECIFIER _Thread_local