Make sure gevent.lock.Semaphore can be weak referenced. This must be...

Make sure gevent.lock.Semaphore can be weak referenced. This must be explicitly declared in cython. Fixes #666.

changelog.rst

@@ -27,6 +27,10 @@
   especially important for PyPy.
 - Request logging by :mod:`gevent.pywsgi` formats the status code
   correctly on Python 3. Reported in :issue:`664` by Kevin Chen.
+- Restore the ability to take a weak reference to instances of exactly
+  :class:`gevent.lock.Semaphore`, which was unintentionally removed
+  as part of making ``Semaphore`` atomic on PyPy on 1.1b1. Reported in
+  :issue:`666` by Ivan-Zhu.
 
 .. _details: https://mail.python.org/pipermail/cython-devel/2015-October/004571.html
 
@@ -162,7 +166,7 @@
 - ``setup.py`` can build with newer versions of clang on OS X. They
   enforce the distinction between CFLAGS and CPPFLAGS.
 - ``gevent.lock.Semaphore`` is atomic on PyPy, just like it is on
-  CPython. This comes at a small performance cost.
+  CPython. This comes at a small performance cost on PyPy.
 - Fixed regression that failed to set the ``successful`` value to
   False when killing a greenlet before it ran with a non-default
   exception. Fixed in :pr:`608` by Heungsub Lee.

gevent/_semaphore.pxd

@@ -3,6 +3,7 @@ cdef class Semaphore:
     cdef readonly object _links
     cdef readonly object _notifier
     cdef public int _dirty
+    cdef object __weakref__
 
     cpdef bint locked(self)
     cpdef int release(self) except -1000

greentest/test__semaphore.py

@@ -2,13 +2,14 @@ import greentest
 import gevent
 from gevent.lock import Semaphore
 from gevent.thread import allocate_lock
+import weakref
 try:
     from _thread import allocate_lock as std_allocate_lock
 except ImportError: # Py2
     from thread import allocate_lock as std_allocate_lock
 
 
-class TestTimeoutAcquire(greentest.TestCase):
+class TestSemaphore(greentest.TestCase):
 
     # issue 39
     def test_acquire_returns_false_after_timeout(self):
@@ -26,6 +27,12 @@ class TestTimeoutAcquire(greentest.TestCase):
         gevent.sleep(0.001)
         self.assertEqual(result, ['a', 'b'])
 
+    def test_semaphore_weakref(self):
+        s = Semaphore()
+        r = weakref.ref(s)
+        self.assertEqual(s, r())
+
+
 
 class TestLock(greentest.TestCase):