Use a descriptor for __module__

This makes the rest of the attribute access fast again, but slows down
__module__.

+-------------------------------------------+------------+-------------------------------+
| Benchmark                                 | 38-master3 | 38-faster-descr               |
+===========================================+============+===============================+
| read __module__                           | 41.1 ns    | 123 ns: 2.99x slower (+199%)  |
+-------------------------------------------+------------+-------------------------------+
| read __name__                             | 41.3 ns    | 39.9 ns: 1.04x faster (-3%)   |
+-------------------------------------------+------------+-------------------------------+
| read __doc__                              | 41.8 ns    | 42.4 ns: 1.01x slower (+1%)   |
+-------------------------------------------+------------+-------------------------------+
| query adapter (no registrations)          | 3.85 ms    | 2.95 ms: 1.30x faster (-23%)  |
+-------------------------------------------+------------+-------------------------------+
| query adapter (all trivial registrations) | 4.59 ms    | 3.67 ms: 1.25x faster (-20%)  |
+-------------------------------------------+------------+-------------------------------+
| contains (empty dict)                     | 136 ns     | 54.8 ns: 2.48x faster (-60%)  |
+-------------------------------------------+------------+-------------------------------+
| contains (populated dict)                 | 137 ns     | 55.7 ns: 2.46x faster (-59%)  |
+-------------------------------------------+------------+-------------------------------+
| contains (populated list)                 | 40.2 us    | 2.86 us: 14.03x faster (-93%) |
+-------------------------------------------+------------+-------------------------------+

Not significant (1): read providedBy

4 files changed, 83 insertions, 48 deletions

diff --git a/src/zope/interface/_compat.py b/src/zope/interface/_compat.py
index a57951a..3587463 100644
--- a/src/zope/interface/_compat.py
+++ b/src/zope/interface/_compat.py
@@ -166,4 +166,5 @@ def _use_c_impl(py_impl, name=None, globs=None):
     # name (for testing and documentation)
     globs[name + 'Py'] = py_impl
     globs[name + 'Fallback'] = py_impl
+
     return c_impl
diff --git a/src/zope/interface/_zope_interface_coptimizations.c b/src/zope/interface/_zope_interface_coptimizations.c
index adc7351..5a4fc92 100644
--- a/src/zope/interface/_zope_interface_coptimizations.c
+++ b/src/zope/interface/_zope_interface_coptimizations.c
@@ -818,6 +818,9 @@ IB_dealloc(IB* self)
 
 static PyMemberDef IB_members[] = {
   {"__name__", T_OBJECT_EX, offsetof(IB, __name__), 0, ""},
+  // The redundancy between __module__ and __ibmodule__ is because
+  // __module__ is often shadowed by subclasses.
+  {"__module__", T_OBJECT_EX, offsetof(IB, __module__), READONLY, ""},
   {"__ibmodule__", T_OBJECT_EX, offsetof(IB, __module__), 0, ""},
   {NULL}
 };
@@ -936,32 +939,21 @@ cleanup:
 
 }
 
-static PyObject*
-IB_getattro(IB* self, PyObject* name)
-{
-    int cmpresult;
-    cmpresult = PyObject_RichCompareBool(name, str__module__, Py_EQ);
-    if (cmpresult == -1)
-        return NULL;
-
-    if (cmpresult) { // __module__
-        if (self->__module__) {
-            Py_INCREF(self->__module__);
-            return self->__module__;
-        }
-    }
-
-    // Wasn't __module__, *or* it was, but it was unset.
-    return PyObject_GenericGetAttr(OBJECT(self), name);
-}
-
 static int
 IB_init(IB* self, PyObject* args, PyObject* kwargs)
 {
+    static char *kwlist[] = {"__name__", "__module__", NULL};
+    PyObject* module = NULL;
+    PyObject* name = NULL;
+
+    if (!PyArg_ParseTupleAndKeywords(args, kwargs, "|OO:InterfaceBase.__init__", kwlist,
+                                      &name, &module)) {
+        return -1;
+    }
     IB_clear(self);
-    self->__module__ = Py_None;
+    self->__module__ = module ? module : Py_None;
     Py_INCREF(self->__module__);
-    self->__name__ = Py_None;
+    self->__name__ = name ? name : Py_None;
     Py_INCREF(self->__name__);
     return 0;
 }
@@ -985,7 +977,7 @@ static PyTypeObject InterfaceBaseType = {
         /* tp_hash           */ (hashfunc)IB_hash,
         /* tp_call           */ (ternaryfunc)ib_call,
         /* tp_str            */ (reprfunc)0,
-        /* tp_getattro       */ (getattrofunc)IB_getattro,
+        /* tp_getattro       */ (getattrofunc)0,
         /* tp_setattro       */ (setattrofunc)0,
         /* tp_as_buffer      */ 0,
         /* tp_flags          */ Py_TPFLAGS_DEFAULT
diff --git a/src/zope/interface/interface.py b/src/zope/interface/interface.py
index d17c8dc..aa66c22 100644
--- a/src/zope/interface/interface.py
+++ b/src/zope/interface/interface.py
@@ -20,6 +20,7 @@ from types import FunctionType
 import weakref
 
 from zope.interface._compat import _use_c_impl
+from zope.interface._compat import PYTHON3 as PY3
 from zope.interface.exceptions import Invalid
 from zope.interface.ro import ro as calculate_ro
 from zope.interface import ro
@@ -238,6 +239,56 @@ class NameAndModuleComparisonMixin(object):
         return c >= 0
 
 
+class _ModuleDescriptor(str):
+    # Descriptor for ``__module__``, used in InterfaceBase and subclasses.
+    #
+    # We store the module value in ``__ibmodule__`` and provide access
+    # to it under ``__module__`` through this descriptor. This is
+    # because we want to store ``__module__`` in the C structure (for
+    # speed of equality and sorting), but it's very hard to do
+    # that. Using PyMemberDef or PyGetSetDef (the C
+    # versions of properties) doesn't work without adding
+    # metaclasses: creating a new subclass puts a ``__module__``
+    # string in the class dict that overrides the descriptor that
+    # would access the C structure data.
+    #
+    # We must also preserve access to the *real* ``__module__`` of the
+    # class.
+    #
+    # Our solution is to watch for new subclasses and manually move
+    # this descriptor into them at creation time. We could use a
+    # metaclass, but this seems safer; using ``__getattribute__`` to
+    # alias the two imposed a 25% penalty on every attribute/method
+    # lookup, even when implemented in C.
+
+    # type.__repr__ accesses self.__dict__['__module__']
+    # and checks to see if it's a native string. If it's not,
+    # the repr just uses the __name__. So for things to work out nicely
+    # it's best for us to subclass str.
+    if PY3:
+        # Python 2 doesn't allow non-empty __slots__ for str
+        # subclasses.
+        __slots__ = ('_class_module',)
+
+    def __init__(self, class_module):
+        str.__init__(self)
+        self._class_module = class_module
+
+    def __get__(self, inst, kind):
+        if inst is None:
+            return self._class_module
+        return inst.__ibmodule__
+
+    def __set__(self, inst, val):
+        # Setting __module__ after construction is undefined. There are
+        # numerous things that cache based on it, either directly or indirectly.
+        # Nonetheless, it is allowed.
+        inst.__ibmodule__ = val
+
+    def __str__(self):
+        return self._class_module
+
+
 @_use_c_impl
 class InterfaceBase(NameAndModuleComparisonMixin, SpecificationBasePy):
     """Base class that wants to be replaced with a C base :)
@@ -246,36 +297,17 @@ class InterfaceBase(NameAndModuleComparisonMixin, SpecificationBasePy):
     __slots__ = (
         '__name__',
         '__ibmodule__',
+        '_v_cached_hash',
     )
 
     def __init__(self, name=None, module=None):
-        # pylint:disable=assigning-non-slot
         self.__name__ = name
-        # We store the module value in ``__ibmodule__`` and provide access
-        # to it under ``__module__`` through ``__getattribute__``. This is
-        # because we want to store __module__ in the C structure (for
-        # speed of equality and sorting), but it's very hard to do
-        # that any other way. Using PyMemberDef or PyGetSetDef (the C
-        # versions of properties) doesn't work without adding
-        # metaclasses: creating a new subclass puts a ``__module__``
-        # string in the class dict that overrides the descriptor that
-        # would access the C structure data.
-        #
-        # We could use a metaclass to override this behaviour, but it's probably
-        # safer to use ``__getattribute__``.
-        #
-        # Setting ``__module__`` after construction is undefined.
-        # There are numerous things that cache that value directly or
-        # indirectly (and long have).
         self.__ibmodule__ = module
 
     def _call_conform(self, conform):
         raise NotImplementedError
 
-    def __getattribute__(self, name):
-        if name == '__module__':
-            return self.__ibmodule__
-        return object.__getattribute__(self, name)
+    __module__ = _ModuleDescriptor(__name__)
 
     def __call__(self, obj, alternate=_marker):
         """Adapt an object to the interface
@@ -559,12 +591,18 @@ class InterfaceClass(InterfaceBase, Element, Specification):
     #
     #implements(IInterface)
 
+    def __new__(cls, *args, **kwargs):
+        if not isinstance(
+                cls.__dict__.get('__module__'),
+                _ModuleDescriptor):
+            cls.__module__ = _ModuleDescriptor(cls.__dict__['__module__'])
+        return super(InterfaceClass, cls).__new__(cls)
+
     def __init__(self, name, bases=(), attrs=None, __doc__=None,  # pylint:disable=redefined-builtin
                  __module__=None):
         if not all(isinstance(base, InterfaceClass) for base in bases):
             raise TypeError('Expected base interfaces')
 
-        InterfaceBase.__init__(self)
         if attrs is None:
             attrs = {}
 
@@ -581,8 +619,10 @@ class InterfaceClass(InterfaceBase, Element, Specification):
                 except (AttributeError, KeyError): # pragma: no cover
                     pass
 
-        self.__ibmodule__ = __module__
+        InterfaceBase.__init__(self, name, __module__)
 
+        assert '__module__' not in self.__dict__
+        assert self.__module__ == __module__, (self.__module__, __module__, self.__ibmodule__)
         d = attrs.get('__doc__')
         if d is not None:
             if not isinstance(d, Attribute):
@@ -799,7 +839,8 @@ class Attribute(Element):
         of = ''
         if self.interface is not None:
             of = self.interface.__module__ + '.' + self.interface.__name__ + '.'
-        return of + self.__name__ + self._get_str_info()
+        # self.__name__ may be None during construction (e.g., debugging)
+        return of + (self.__name__ or '<unknown>') + self._get_str_info()
 
     def __repr__(self):
         return "<%s.%s object at 0x%x %s>" % (
diff --git a/src/zope/interface/tests/test_registry.py b/src/zope/interface/tests/test_registry.py
index db91c52..2df4ae8 100644
--- a/src/zope/interface/tests/test_registry.py
+++ b/src/zope/interface/tests/test_registry.py
@@ -2343,9 +2343,10 @@ class UtilityRegistrationTests(unittest.TestCase):
     def _makeOne(self, component=None, factory=None):
         from zope.interface.declarations import InterfaceClass
 
-        class IFoo(InterfaceClass):
+        class InterfaceClassSubclass(InterfaceClass):
             pass
-        ifoo = IFoo('IFoo')
+
+        ifoo = InterfaceClassSubclass('IFoo')
         class _Registry(object):
             def __repr__(self):
                 return '_REGISTRY'