Disable profiler on Ruby 3.3 when running with RUBY_MN_THREADS=1

ext/ddtrace_profiling_native_extension/clock_id_from_pthread.c

@@ -25,6 +25,9 @@ void self_test_clock_id(void) {
 // Safety: This function is assumed never to raise exceptions by callers
 thread_cpu_time_id thread_cpu_time_id_for(VALUE thread) {
   rb_nativethread_id_t thread_id = pthread_id_for(thread);
+
+  if (thread_id == 0) return (thread_cpu_time_id) {.valid = false};
+
   clockid_t clock_id;
 
   int error = pthread_getcpuclockid(thread_id, &clock_id);

ext/ddtrace_profiling_native_extension/extconf.rb

@@ -134,6 +134,9 @@ def add_compiler_flag(flag)
   $defs << '-DHAVE_PTHREAD_GETCPUCLOCKID'
 end
 
+# On older Rubies, M:N threads were not available
+$defs << '-DNO_MN_THREADS_AVAILABLE' if RUBY_VERSION < '3.3'
+
 # On older Rubies, we did not need to include the ractor header (this was built into the MJIT header)
 $defs << '-DNO_RACTOR_HEADER_INCLUDE' if RUBY_VERSION < '3.3'
 

ext/ddtrace_profiling_native_extension/private_vm_api_access.c

@@ -58,9 +58,12 @@ static inline rb_thread_t *thread_struct_from_object(VALUE thread) {
 }
 
 rb_nativethread_id_t pthread_id_for(VALUE thread) {
-  // struct rb_native_thread was introduced in Ruby 3.2 (preview2): https://github.com/ruby/ruby/pull/5836
+  // struct rb_native_thread was introduced in Ruby 3.2: https://github.com/ruby/ruby/pull/5836
   #ifndef NO_RB_NATIVE_THREAD
-    return thread_struct_from_object(thread)->nt->thread_id;
+    struct rb_native_thread* native_thread = thread_struct_from_object(thread)->nt;
+    // This can be NULL on Ruby 3.3 with MN threads (RUBY_MN_THREADS=1)
+    if (native_thread == NULL) return 0;
+    return native_thread->thread_id;
   #else
     return thread_struct_from_object(thread)->thread_id;
   #endif
@@ -113,15 +116,16 @@ bool is_current_thread_holding_the_gvl(void) {
 
     if (current_owner == NULL) return (current_gvl_owner) {.valid = false};
 
-    return (current_gvl_owner) {
-      .valid = true,
-      .owner =
-        #ifndef NO_RB_NATIVE_THREAD
-          current_owner->nt->thread_id
-        #else
-          current_owner->thread_id
-        #endif
-    };
+    #ifndef NO_RB_NATIVE_THREAD
+      struct rb_native_thread* current_owner_native_thread = current_owner->nt;
+
+      // This can be NULL on Ruby 3.3 with MN threads (RUBY_MN_THREADS=1)
+      if (current_owner_native_thread == NULL) return (current_gvl_owner) {.valid = false};
+
+      return (current_gvl_owner) {.valid = true, .owner = current_owner_native_thread->thread_id};
+    #else
+      return (current_gvl_owner) {.valid = true, .owner = current_owner->thread_id};
+    #endif
   }
 #else
   current_gvl_owner gvl_owner(void) {
@@ -182,7 +186,9 @@ uint64_t native_thread_id_for(VALUE thread) {
   // The tid is only available on Ruby >= 3.1 + Linux (and FreeBSD). It's the same as `gettid()` aka the task id as seen in /proc
   #if !defined(NO_THREAD_TID) && defined(RB_THREAD_T_HAS_NATIVE_ID)
     #ifndef NO_RB_NATIVE_THREAD
-      return thread_struct_from_object(thread)->nt->tid;
+      struct rb_native_thread* native_thread = thread_struct_from_object(thread)->nt;
+      if (native_thread == NULL) rb_raise(rb_eRuntimeError, "BUG: rb_native_thread* is null. Is this Ruby running with RUBY_MN_THREADS=1?");
+      return native_thread->tid;
     #else
       return thread_struct_from_object(thread)->tid;
     #endif
@@ -811,3 +817,13 @@ VALUE invoke_location_for(VALUE thread, int *line_location) {
   *line_location = NUM2INT(rb_iseq_first_lineno(iseq));
   return rb_iseq_path(iseq);
 }
+
+void self_test_mn_enabled(void) {
+  #ifdef NO_MN_THREADS_AVAILABLE
+    return;
+  #else
+    if (ddtrace_get_ractor()->threads.sched.enable_mn_threads == true) {
+      rb_raise(rb_eRuntimeError, "Ruby VM is running with RUBY_MN_THREADS=1. This is not yet supported");
+    }
+  #endif
+}

ext/ddtrace_profiling_native_extension/private_vm_api_access.h

@@ -49,3 +49,6 @@ bool ddtrace_rb_ractor_main_p(void);
 // This is what Ruby shows in `Thread#to_s`.
 // The file is returned directly, and the line is recorded onto *line_location.
 VALUE invoke_location_for(VALUE thread, int *line_location);
+
+// Check if RUBY_MN_THREADS is enabled (aka main Ractor is not doing 1:1 threads)
+void self_test_mn_enabled(void);

ext/ddtrace_profiling_native_extension/profiling.c

@@ -68,6 +68,7 @@ void DDTRACE_EXPORT Init_ddtrace_profiling_native_extension(void) {
 
 static VALUE native_working_p(DDTRACE_UNUSED VALUE _self) {
   self_test_clock_id();
+  self_test_mn_enabled();
 
   return Qtrue;
 }