patcher: set locked RLocks' owner only when patching existing locks

For Python 2, patching existing locks replaces RLock._RLock__owner with current
thread ID no matter the old lock is locked or not and thus an unlocked RLock
would have a non None owner (e.g. <_RLock owner=140106584489808 count=0>).
Then if we acquire the RLock in the same thread, the method RLock.acquire would
not invoke the _RLock__block.acquire() since it treats this is a recursive
acquire by checking current thread ID. And then the following RLock.release
would invoke the _RLock__block.release method resulting in the counter of
Semaphore being improved to 2.

There should be only two states being expected for RLock:
1. owner != None and count > 0
2. owner == None and count == 0

This patch fixs it by only setting locked RLocks' owner during patching.

eventlet/patcher.py

@@ -358,7 +358,7 @@ def _fix_py2_rlock(rlock, tid):
     rlock._RLock__block = new
     if old.locked():
         new.acquire()
-    rlock._RLock__owner = tid
+        rlock._RLock__owner = tid
 
 
 def _fix_py3_rlock(old):

tests/__init__.py

@@ -123,6 +123,15 @@ def skip_if_no_itimer(func):
     return skip_unless(has_itimer)(func)
 
 
+def skip_if_CRLock_exist(func):
+    """ Decorator that skips a test if the `_thread.RLock` class exists """
+    try:
+        from _thread import RLock
+        return skipped(func)
+    except ImportError:
+        return func
+
+
 def skip_if_no_ssl(func):
     """ Decorator that skips a test if SSL is not available."""
     try:

tests/isolated/patcher_existing_locks_unlocked.py

@@ -0,0 +1,25 @@
+__test__ = False
+
+
+def take(lock, e1, e2):
+    with lock:
+        e1.set()
+        e2.wait()
+
+
+if __name__ == '__main__':
+    import sys
+    import threading
+    lock = threading.RLock()
+    import eventlet
+    eventlet.monkey_patch()
+
+    lock.acquire()
+    lock.release()
+
+    e1, e2 = threading.Event(), threading.Event()
+    eventlet.spawn(take, lock, e1, e2)
+    e1.wait()
+    assert not lock.acquire(blocking=0)
+    e2.set()
+    print('pass')

tests/patcher_test.py

@@ -493,6 +493,11 @@ def test_patcher_existing_locks_locked():
     tests.run_isolated('patcher_existing_locks_locked.py')
 
 
+@tests.skip_if_CRLock_exist
+def test_patcher_existing_locks_unlocked():
+    tests.run_isolated('patcher_existing_locks_unlocked.py')
+
+
 def test_importlib_lock():
     tests.run_isolated('patcher_importlib_lock.py')