Fix potential hang when joining threads.

If the thread termination invokes user code after `th->status` becomes
`THREAD_KILLED`, and the user unblock function causes that `th->status` to
become something else (e.g. `THREAD_RUNNING`), threads waiting in
`thread_join_sleep` will hang forever. We move the unblock function call
to before the thread status is updated, and allow threads to join as soon
as `th->value` becomes defined.

This reverts commit 6505c77501f1924571b2fe620c5c7b31ede0cd22.

1 files changed, 14 insertions, 2 deletions

diff --git a/test/fiber/scheduler.rb b/test/fiber/scheduler.rb
index 0553e386f5..df82c2ff93 100644
--- a/test/fiber/scheduler.rb
+++ b/test/fiber/scheduler.rb
@@ -100,8 +100,10 @@ class Scheduler
 
     self.run
   ensure
-    @urgent.each(&:close)
-    @urgent = nil
+    if @urgent
+      @urgent.each(&:close)
+      @urgent = nil
+    end
 
     @closed = true
 
@@ -196,3 +198,13 @@ class BrokenUnblockScheduler < Scheduler
     raise "Broken unblock!"
   end
 end
+
+class SleepingUnblockScheduler < Scheduler
+  # This method is invoked when the thread is exiting.
+  def unblock(blocker, fiber)
+    super
+
+    # This changes the current thread state to `THREAD_RUNNING` which causes `thread_join_sleep` to hang.
+    sleep(0.1)
+  end
+end