Only interrupt when there is no scheduler in sync_wakeup()

* When there is a scheduler, the Fiber that would be blocked has already
  been rescheduled and there is no point to interrupt something else.
  That blocked Fiber will be rescheduled as the next call to the scheduler
  (e.g., IO, sleep, other blocking sync).
* See discussion on https://github.com/ruby/ruby/commit/d01954632d

1 files changed, 4 insertions, 2 deletions

diff --git a/thread_sync.c b/thread_sync.c
index 41df2dead9..748ccbd558 100644
--- a/thread_sync.c
+++ b/thread_sync.c
@@ -34,8 +34,10 @@ sync_wakeup(struct list_head *head, long max)
         }
 
         if (cur->th->status != THREAD_KILLED) {
-            rb_threadptr_interrupt(cur->th);
-            cur->th->status = THREAD_RUNNABLE;
+            if (cur->th->scheduler != Qnil) {
+                rb_threadptr_interrupt(cur->th);
+                cur->th->status = THREAD_RUNNABLE;
+            }
             if (--max == 0) return;
         }
     }