Add backports.socketpair as test/recommended extra on Windows/Py2

We use it in our selector tests.

appveyor.yml

@@ -40,6 +40,11 @@ environment:
     # a later point release.
 
     # 64-bit
+    - PYTHON: "C:\\Python27-x64"
+      PYTHON_VERSION: "2.7.x" # currently 2.7.13
+      PYTHON_ARCH: "64"
+      PYTHON_EXE: python
+
     - PYTHON: "C:\\Python38-x64"
       PYTHON_VERSION: "3.8.x"
       PYTHON_ARCH: "64"
@@ -50,11 +55,6 @@ environment:
       PYTHON_ARCH: "64"
       PYTHON_EXE: python
 
-    - PYTHON: "C:\\Python27-x64"
-      PYTHON_VERSION: "2.7.x" # currently 2.7.13
-      PYTHON_ARCH: "64"
-      PYTHON_EXE: python
-
     - PYTHON: "C:\\Python36-x64"
       PYTHON_VERSION: "3.6.x" # currently 3.6.0
       PYTHON_ARCH: "64"

docs/install.rst

@@ -146,7 +146,13 @@ monitor
     build on all platforms.)
 
 recommended
-    A shortcut for installing suggested extras together.
+    A shortcut for installing suggested extras together. This includes
+    the non-test extras defined here, plus:
+
+    - `backports.socketpair
+      <https://pypi.org/project/backports.socketpair/>`_ on Python
+      2/Windows (beginning with release 20.6.0);
+    - `selectors2 <https://pypi.org/project/selectors2/>`_ on Python 2 (beginning with release 20.6.0).
 
 test
     Everything needed to run the complete gevent test suite.

setup.py

@@ -317,6 +317,8 @@ EXTRA_RECOMMENDED = [
     CFFI_DEP,
     # Backport of selectors module to Python 2
     'selectors2 ; python_version == "2.7"',
+    # Backport of socket.socketpair to Python 2; only needed on Windows
+    'backports.socketpair ; python_version == "2.7" and sys_platform == "win32"',
 ] + EXTRA_DNSPYTHON + EXTRA_EVENTS + EXTRA_MONITOR
 
 

src/gevent/_abstract_linkable.py

@@ -194,6 +194,10 @@ class AbstractLinkable(object):
         # The object itself becomes false in a boolean way as soon
         # as this method returns.
         notifier = self._notifier
+        if notifier is None:
+            # XXX: How did we get here?
+            self._check_and_notify()
+            return
         # Early links are allowed to remove later links, and links
         # are allowed to add more links, thus we must not
         # make a copy of our the ``_links`` list, we must traverse it and

src/gevent/_socket2.py

@@ -460,7 +460,8 @@ class socket(_socketcommon.SocketMixin):
 SocketType = socket
 
 if hasattr(_socket, 'socketpair'):
-
+    # The native, low-level socketpair returns
+    # low-level objects
     def socketpair(family=getattr(_socket, 'AF_UNIX', _socket.AF_INET),
                    type=_socket.SOCK_STREAM, proto=0):
         one, two = _socket.socketpair(family, type, proto)
@@ -469,6 +470,20 @@ if hasattr(_socket, 'socketpair'):
             one._drop()
             two._drop()
         return result
+elif hasattr(__socket__, 'socketpair'):
+    # The high-level backport uses high-level socket APIs. It works
+    # cooperatively automatically if we're monkey-patched,
+    # else we must do it ourself.
+    _orig_socketpair = __socket__.socketpair
+    def socketpair(*args, **kwargs):
+        one, two = _orig_socketpair(*args, **kwargs)
+        if not isinstance(one, socket):
+            one = socket(_sock=one)
+            two = socket(_sock=two)
+            if PYPY:
+                one._drop()
+                two._drop()
+        return one, two
 elif 'socketpair' in __implements__:
     __implements__.remove('socketpair')
 

src/gevent/_socketcommon.py

@@ -128,6 +128,11 @@ if is_macos:
 import _socket
 _realsocket = _socket.socket
 import socket as __socket__
+try:
+    # Provide implementation of socket.socketpair on Windows < 3.5.
+    import backports.socketpair
+except ImportError:
+    pass
 
 _name = _value = None
 __imports__ = copy_globals(__socket__, globals(),

src/gevent/tests/known_failures.py

@@ -259,14 +259,6 @@ class Definitions(DefinitionsBase):
         when=APPVEYOR & PY3
     )
 
-    test__socketpair = Ignored(
-        """
-        Py35 added socket.socketpair, all other releases
-        are missing it. No reason to even test it.
-        """,
-        when=WIN & PY2
-    )
-
     test_ftplib = Flaky(
         r"""
         could be a problem of appveyor - not sure

src/gevent/tests/test__socketpair.py

@@ -15,6 +15,8 @@ class TestSocketpair(unittest.TestCase):
         self.assertEqual(msg, read)
         y.close()
 
+    @unittest.skipUnless(hasattr(socket, 'fromfd'),
+                         'Needs socket.fromfd')
     def test_fromfd(self):
         msg = b'hello world'
         x, y = socket.socketpair()