Drop the thread's reference to the greenlet when we're done with it under Python3.4.

gevent/threading.py

@@ -65,6 +65,13 @@ if sys.version_info[:2] >= (3, 4):
         def _set_tstate_lock(self):
             self._greenlet = getcurrent()
 
+        def run(self):
+            try:
+                super(Thread, self).run()
+            finally:
+                del self._greenlet # avoid ref cycles
+                self._stop() # mark as finished
+
         def join(self, timeout=None):
             if self._greenlet is None:
                 return

greentest/test__socket.py

@@ -32,7 +32,6 @@ class Thread(_Thread):
         target = kwargs.pop('target')
         target = wrap_error(target)
         _Thread.__init__(self, target=target, **kwargs)
-        self.daemon = True
         self.start()
 
 

known_failures.py

@@ -131,6 +131,7 @@ FLAKY test__socket_dns.py
             test__socket_close.py
             test__select.py
             test__greenlet.py
+            FLAKY test__socket.py
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