When setting current thread scheduler to nil, invoke `#close`.

1 files changed, 6 insertions, 4 deletions

diff --git a/thread.c b/thread.c
index b3b7a69305..53bfbe8562 100644
--- a/thread.c
+++ b/thread.c
@@ -748,10 +748,7 @@ thread_do_start(rb_thread_t *th)
         rb_bug("unreachable");
     }
 
-    VALUE scheduler = th->scheduler;
-    if (scheduler != Qnil) {
-        rb_funcall(scheduler, rb_intern("run"), 0);
-    }
+    rb_thread_scheduler_set(th->self, Qnil);
 }
 
 void rb_ec_clear_current_thread_trace_func(const rb_execution_context_t *ec);
@@ -3732,6 +3729,11 @@ rb_thread_scheduler_set(VALUE thread, VALUE scheduler)
 
     VM_ASSERT(th);
 
+    // We invoke Scheduler#close when setting it to something else, to ensure the previous scheduler runs to completion before changing the scheduler. That way, we do not need to consider interactions, e.g., of a Fiber from the previous scheduler with the new scheduler.
+    if (th->scheduler != Qnil) {
+        rb_scheduler_close(th->scheduler);
+    }
+
     th->scheduler = scheduler;
 
     return th->scheduler;