Fix Thread#join(timeout) when running inside the fiber scheduler. (#7903)

Merged-By: ioquatix <samuel@codeotaku.com>

test/fiber/test_thread.rb

@@ -20,6 +20,28 @@ class TestFiberThread < Test::Unit::TestCase
     assert_equal :done, thread.value
   end
 
+  def test_thread_join_timeout
+    sleeper = nil
+
+    thread = Thread.new do
+      scheduler = Scheduler.new
+      Fiber.set_scheduler scheduler
+
+      Fiber.schedule do
+        sleeper = Thread.new{sleep}
+        sleeper.join(0.1)
+      end
+
+      scheduler.run
+    end
+
+    thread.join
+
+    assert_predicate sleeper, :alive?
+  ensure
+    sleeper&.kill
+  end
+
   def test_thread_join_implicit
     sleeping = false
     finished = false

thread.c

@@ -1053,6 +1053,10 @@ thread_join_sleep(VALUE arg)
 
         if (scheduler != Qnil) {
             rb_fiber_scheduler_block(scheduler, target_th->self, p->timeout);
+            // Check if the target thread is finished after blocking:
+            if (thread_finished(target_th)) break;
+            // Otherwise, a timeout occurred:
+            else return Qfalse;
         }
         else if (!limit) {
             sleep_forever(th, SLEEP_DEADLOCKABLE | SLEEP_ALLOW_SPURIOUS | SLEEP_NO_CHECKINTS);
@@ -1070,6 +1074,7 @@ thread_join_sleep(VALUE arg)
 
         RUBY_DEBUG_LOG("interrupted target_th:%u status:%s", rb_th_serial(target_th), thread_status_name(target_th, TRUE));
     }
+
     return Qtrue;
 }