`rb_thread_lock_native_thread()`

Introduce `rb_thread_lock_native_thread()` to allocate dedicated
native thread to the current Ruby thread for M:N threads.
This C API is similar to Go's `runtime.LockOSThread()`.

Accepted at https://github.com/ruby/dev-meeting-log/blob/master/2023/DevMeeting-2023-08-24.md
(and missed to implement on Ruby 3.3.0)

1 files changed, 17 insertions, 0 deletions

diff --git a/thread_pthread.c b/thread_pthread.c
index 580df826da..fb446eee82 100644
--- a/thread_pthread.c
+++ b/thread_pthread.c
@@ -2304,6 +2304,11 @@ nt_start(void *ptr)
                 // timeout -> deleted.
                 break;
             }
+
+            if (nt->dedicated) {
+                // SNT becomes DNT while running
+                break;
+            }
         }
     }
 
@@ -3422,4 +3427,16 @@ rb_thread_execute_hooks(rb_event_flag_t event, rb_thread_t *th)
     }
 }
 
+// return true if the current thread acquires DNT.
+// return false if the current thread already acquires DNT.
+bool
+rb_thread_lock_native_thread(void)
+{
+    rb_thread_t *th = GET_THREAD();
+    bool is_snt = th->nt->dedicated == 0;
+    native_thread_dedicated_inc(th->vm, th->ractor, th->nt);
+
+    return is_snt;
+}
+
 #endif /* THREAD_SYSTEM_DEPENDENT_IMPLEMENTATION */