Make the connection stack thread safe.

For this, I've included Werkzeug's context locals, which offers both
thread and greenlet safe local variables.

This fixes #47.

rq/connections.py

@@ -1,41 +1,12 @@
 from contextlib import contextmanager
 from redis import Redis
+from .local import LocalStack, release_local
 
 
 class NoRedisConnectionException(Exception):
     pass
 
 
-class _RedisConnectionStack(object):
-    def __init__(self):
-        self.stack = []
-
-    def _get_current_object(self):
-        try:
-            return self.stack[-1]
-        except IndexError:
-            msg = 'No Redis connection configured.'
-            raise NoRedisConnectionException(msg)
-
-    def pop(self):
-        return self.stack.pop()
-
-    def push(self, connection):
-        self.stack.append(connection)
-
-    def empty(self):
-        del self.stack[:]
-
-    def depth(self):
-        return len(self.stack)
-
-    def __getattr__(self, name):
-        return getattr(self._get_current_object(), name)
-
-
-_connection_stack = _RedisConnectionStack()
-
-
 @contextmanager
 def Connection(connection=None):
     if connection is None:
@@ -64,21 +35,23 @@ def use_connection(redis=None):
     """Clears the stack and uses the given connection.  Protects against mixed
     use of use_connection() and stacked connection contexts.
     """
-    assert _connection_stack.depth() <= 1, \
+    assert len(_connection_stack) <= 1, \
             'You should not mix Connection contexts with use_connection().'
-    _connection_stack.empty()
+    release_local(_connection_stack)
 
     if redis is None:
         redis = Redis()
-    push_connection(redis)
+    _connection_stack.push(redis)
 
 
 def get_current_connection():
     """Returns the current Redis connection (i.e. the topmost on the
     connection stack).
     """
-    return _connection_stack._get_current_object()
+    return _connection_stack.top
+
 
+_connection_stack = LocalStack()
 
 __all__ = ['Connection',
         'get_current_connection', 'push_connection', 'pop_connection',

rq/local.py

@@ -0,0 +1,371 @@
+# -*- coding: utf-8 -*-
+"""
+    werkzeug.local
+    ~~~~~~~~~~~~~~
+
+    This module implements context-local objects.
+
+    :copyright: (c) 2011 by the Werkzeug Team, see AUTHORS for more details.
+    :license: BSD, see LICENSE for more details.
+"""
+# Since each thread has its own greenlet we can just use those as identifiers
+# for the context.  If greenlets are not available we fall back to the
+# current thread ident.
+try:
+    from greenlet import getcurrent as get_ident
+except ImportError: # noqa
+    try:
+        from thread import get_ident  # noqa
+    except ImportError: # noqa
+        from dummy_thread import get_ident  # noqa
+
+
+def release_local(local):
+    """Releases the contents of the local for the current context.
+    This makes it possible to use locals without a manager.
+
+    Example::
+
+        >>> loc = Local()
+        >>> loc.foo = 42
+        >>> release_local(loc)
+        >>> hasattr(loc, 'foo')
+        False
+
+    With this function one can release :class:`Local` objects as well
+    as :class:`StackLocal` objects.  However it is not possible to
+    release data held by proxies that way, one always has to retain
+    a reference to the underlying local object in order to be able
+    to release it.
+
+    .. versionadded:: 0.6.1
+    """
+    local.__release_local__()
+
+
+class Local(object):
+    __slots__ = ('__storage__', '__ident_func__')
+
+    def __init__(self):
+        object.__setattr__(self, '__storage__', {})
+        object.__setattr__(self, '__ident_func__', get_ident)
+
+    def __iter__(self):
+        return iter(self.__storage__.items())
+
+    def __call__(self, proxy):
+        """Create a proxy for a name."""
+        return LocalProxy(self, proxy)
+
+    def __release_local__(self):
+        self.__storage__.pop(self.__ident_func__(), None)
+
+    def __getattr__(self, name):
+        try:
+            return self.__storage__[self.__ident_func__()][name]
+        except KeyError:
+            raise AttributeError(name)
+
+    def __setattr__(self, name, value):
+        ident = self.__ident_func__()
+        storage = self.__storage__
+        try:
+            storage[ident][name] = value
+        except KeyError:
+            storage[ident] = {name: value}
+
+    def __delattr__(self, name):
+        try:
+            del self.__storage__[self.__ident_func__()][name]
+        except KeyError:
+            raise AttributeError(name)
+
+
+class LocalStack(object):
+    """This class works similar to a :class:`Local` but keeps a stack
+    of objects instead.  This is best explained with an example::
+
+        >>> ls = LocalStack()
+        >>> ls.push(42)
+        >>> ls.top
+        42
+        >>> ls.push(23)
+        >>> ls.top
+        23
+        >>> ls.pop()
+        23
+        >>> ls.top
+        42
+
+    They can be force released by using a :class:`LocalManager` or with
+    the :func:`release_local` function but the correct way is to pop the
+    item from the stack after using.  When the stack is empty it will
+    no longer be bound to the current context (and as such released).
+
+    By calling the stack without arguments it returns a proxy that resolves to
+    the topmost item on the stack.
+
+    .. versionadded:: 0.6.1
+    """
+
+    def __init__(self):
+        self._local = Local()
+
+    def __release_local__(self):
+        self._local.__release_local__()
+
+    def _get__ident_func__(self):
+        return self._local.__ident_func__
+    def _set__ident_func__(self, value):  # noqa
+        object.__setattr__(self._local, '__ident_func__', value)
+    __ident_func__ = property(_get__ident_func__, _set__ident_func__)
+    del _get__ident_func__, _set__ident_func__
+
+    def __call__(self):
+        def _lookup():
+            rv = self.top
+            if rv is None:
+                raise RuntimeError('object unbound')
+            return rv
+        return LocalProxy(_lookup)
+
+    def push(self, obj):
+        """Pushes a new item to the stack"""
+        rv = getattr(self._local, 'stack', None)
+        if rv is None:
+            self._local.stack = rv = []
+        rv.append(obj)
+        return rv
+
+    def pop(self):
+        """Removes the topmost item from the stack, will return the
+        old value or `None` if the stack was already empty.
+        """
+        stack = getattr(self._local, 'stack', None)
+        if stack is None:
+            return None
+        elif len(stack) == 1:
+            release_local(self._local)
+            return stack[-1]
+        else:
+            return stack.pop()
+
+    @property
+    def top(self):
+        """The topmost item on the stack.  If the stack is empty,
+        `None` is returned.
+        """
+        try:
+            return self._local.stack[-1]
+        except (AttributeError, IndexError):
+            return None
+
+    def __len__(self):
+        return len(self._local.stack)
+
+
+class LocalManager(object):
+    """Local objects cannot manage themselves. For that you need a local
+    manager.  You can pass a local manager multiple locals or add them later
+    by appending them to `manager.locals`.  Everytime the manager cleans up
+    it, will clean up all the data left in the locals for this context.
+
+    The `ident_func` parameter can be added to override the default ident
+    function for the wrapped locals.
+
+    .. versionchanged:: 0.6.1
+       Instead of a manager the :func:`release_local` function can be used
+       as well.
+
+    .. versionchanged:: 0.7
+       `ident_func` was added.
+    """
+
+    def __init__(self, locals=None, ident_func=None):
+        if locals is None:
+            self.locals = []
+        elif isinstance(locals, Local):
+            self.locals = [locals]
+        else:
+            self.locals = list(locals)
+        if ident_func is not None:
+            self.ident_func = ident_func
+            for local in self.locals:
+                object.__setattr__(local, '__ident_func__', ident_func)
+        else:
+            self.ident_func = get_ident
+
+    def get_ident(self):
+        """Return the context identifier the local objects use internally for
+        this context.  You cannot override this method to change the behavior
+        but use it to link other context local objects (such as SQLAlchemy's
+        scoped sessions) to the Werkzeug locals.
+
+        .. versionchanged:: 0.7
+           Yu can pass a different ident function to the local manager that
+           will then be propagated to all the locals passed to the
+           constructor.
+        """
+        return self.ident_func()
+
+    def cleanup(self):
+        """Manually clean up the data in the locals for this context.  Call
+        this at the end of the request or use `make_middleware()`.
+        """
+        for local in self.locals:
+            release_local(local)
+
+    def __repr__(self):
+        return '<%s storages: %d>' % (
+            self.__class__.__name__,
+            len(self.locals)
+        )
+
+
+class LocalProxy(object):
+    """Acts as a proxy for a werkzeug local.  Forwards all operations to
+    a proxied object.  The only operations not supported for forwarding
+    are right handed operands and any kind of assignment.
+
+    Example usage::
+
+        from werkzeug.local import Local
+        l = Local()
+
+        # these are proxies
+        request = l('request')
+        user = l('user')
+
+
+        from werkzeug.local import LocalStack
+        _response_local = LocalStack()
+
+        # this is a proxy
+        response = _response_local()
+
+    Whenever something is bound to l.user / l.request the proxy objects
+    will forward all operations.  If no object is bound a :exc:`RuntimeError`
+    will be raised.
+
+    To create proxies to :class:`Local` or :class:`LocalStack` objects,
+    call the object as shown above.  If you want to have a proxy to an
+    object looked up by a function, you can (as of Werkzeug 0.6.1) pass
+    a function to the :class:`LocalProxy` constructor::
+
+        session = LocalProxy(lambda: get_current_request().session)
+
+    .. versionchanged:: 0.6.1
+       The class can be instanciated with a callable as well now.
+    """
+    __slots__ = ('__local', '__dict__', '__name__')
+
+    def __init__(self, local, name=None):
+        object.__setattr__(self, '_LocalProxy__local', local)
+        object.__setattr__(self, '__name__', name)
+
+    def _get_current_object(self):
+        """Return the current object.  This is useful if you want the real
+        object behind the proxy at a time for performance reasons or because
+        you want to pass the object into a different context.
+        """
+        if not hasattr(self.__local, '__release_local__'):
+            return self.__local()
+        try:
+            return getattr(self.__local, self.__name__)
+        except AttributeError:
+            raise RuntimeError('no object bound to %s' % self.__name__)
+
+    @property
+    def __dict__(self):
+        try:
+            return self._get_current_object().__dict__
+        except RuntimeError:
+            raise AttributeError('__dict__')
+
+    def __repr__(self):
+        try:
+            obj = self._get_current_object()
+        except RuntimeError:
+            return '<%s unbound>' % self.__class__.__name__
+        return repr(obj)
+
+    def __nonzero__(self):
+        try:
+            return bool(self._get_current_object())
+        except RuntimeError:
+            return False
+
+    def __unicode__(self):
+        try:
+            return unicode(self._get_current_object())
+        except RuntimeError:
+            return repr(self)
+
+    def __dir__(self):
+        try:
+            return dir(self._get_current_object())
+        except RuntimeError:
+            return []
+
+    def __getattr__(self, name):
+        if name == '__members__':
+            return dir(self._get_current_object())
+        return getattr(self._get_current_object(), name)
+
+    def __setitem__(self, key, value):
+        self._get_current_object()[key] = value
+
+    def __delitem__(self, key):
+        del self._get_current_object()[key]
+
+    def __setslice__(self, i, j, seq):
+        self._get_current_object()[i:j] = seq
+
+    def __delslice__(self, i, j):
+        del self._get_current_object()[i:j]
+
+    __setattr__ = lambda x, n, v: setattr(x._get_current_object(), n, v)
+    __delattr__ = lambda x, n: delattr(x._get_current_object(), n)
+    __str__ = lambda x: str(x._get_current_object())
+    __lt__ = lambda x, o: x._get_current_object() < o
+    __le__ = lambda x, o: x._get_current_object() <= o
+    __eq__ = lambda x, o: x._get_current_object() == o
+    __ne__ = lambda x, o: x._get_current_object() != o
+    __gt__ = lambda x, o: x._get_current_object() > o
+    __ge__ = lambda x, o: x._get_current_object() >= o
+    __cmp__ = lambda x, o: cmp(x._get_current_object(), o)
+    __hash__ = lambda x: hash(x._get_current_object())
+    __call__ = lambda x, *a, **kw: x._get_current_object()(*a, **kw)
+    __len__ = lambda x: len(x._get_current_object())
+    __getitem__ = lambda x, i: x._get_current_object()[i]
+    __iter__ = lambda x: iter(x._get_current_object())
+    __contains__ = lambda x, i: i in x._get_current_object()
+    __getslice__ = lambda x, i, j: x._get_current_object()[i:j]
+    __add__ = lambda x, o: x._get_current_object() + o
+    __sub__ = lambda x, o: x._get_current_object() - o
+    __mul__ = lambda x, o: x._get_current_object() * o
+    __floordiv__ = lambda x, o: x._get_current_object() // o
+    __mod__ = lambda x, o: x._get_current_object() % o
+    __divmod__ = lambda x, o: x._get_current_object().__divmod__(o)
+    __pow__ = lambda x, o: x._get_current_object() ** o
+    __lshift__ = lambda x, o: x._get_current_object() << o
+    __rshift__ = lambda x, o: x._get_current_object() >> o
+    __and__ = lambda x, o: x._get_current_object() & o
+    __xor__ = lambda x, o: x._get_current_object() ^ o
+    __or__ = lambda x, o: x._get_current_object() | o
+    __div__ = lambda x, o: x._get_current_object().__div__(o)
+    __truediv__ = lambda x, o: x._get_current_object().__truediv__(o)
+    __neg__ = lambda x: -(x._get_current_object())
+    __pos__ = lambda x: +(x._get_current_object())
+    __abs__ = lambda x: abs(x._get_current_object())
+    __invert__ = lambda x: ~(x._get_current_object())
+    __complex__ = lambda x: complex(x._get_current_object())
+    __int__ = lambda x: int(x._get_current_object())
+    __long__ = lambda x: long(x._get_current_object())
+    __float__ = lambda x: float(x._get_current_object())
+    __oct__ = lambda x: oct(x._get_current_object())
+    __hex__ = lambda x: hex(x._get_current_object())
+    __index__ = lambda x: x._get_current_object().__index__()
+    __coerce__ = lambda x, o: x._get_current_object().__coerce__(x, o)
+    __enter__ = lambda x: x._get_current_object().__enter__()
+    __exit__ = lambda x, *a, **kw: x._get_current_object().__exit__(*a, **kw)