Update Tornado lib

libs/tornado/util.py

@@ -96,6 +96,102 @@ def raise_exc_info(exc_info):
         # After 2to3: raise exc_info[0](exc_info[1]).with_traceback(exc_info[2])
 
 
+class Configurable(object):
+    """Base class for configurable interfaces.
+
+    A configurable interface is an (abstract) class whose constructor
+    acts as a factory function for one of its implementation subclasses.
+    The implementation subclass as well as optional keyword arguments to
+    its initializer can be set globally at runtime with `configure`.
+
+    By using the constructor as the factory method, the interface looks like
+    a normal class, ``isinstance()`` works as usual, etc.  This pattern
+    is most useful when the choice of implementation is likely to be a
+    global decision (e.g. when epoll is available, always use it instead of
+    select), or when a previously-monolithic class has been split into
+    specialized subclasses.
+
+    Configurable subclasses must define the class methods
+    `configurable_base` and `configurable_default`, and use the instance
+    method `initialize` instead of `__init__`.
+    """
+    __impl_class = None
+    __impl_kwargs = None
+
+    def __new__(cls, **kwargs):
+        base = cls.configurable_base()
+        args = {}
+        if cls is base:
+            impl = cls.configured_class()
+            if base.__impl_kwargs:
+                args.update(base.__impl_kwargs)
+        else:
+            impl = cls
+        args.update(kwargs)
+        instance = super(Configurable, cls).__new__(impl)
+        # initialize vs __init__ chosen for compatiblity with AsyncHTTPClient
+        # singleton magic.  If we get rid of that we can switch to __init__
+        # here too.
+        instance.initialize(**args)
+        return instance
+
+    @classmethod
+    def configurable_base(cls):
+        """Returns the base class of a configurable hierarchy.
+
+        This will normally return the class in which it is defined.
+        (which is *not* necessarily the same as the cls classmethod parameter).
+        """
+        raise NotImplementedError()
+
+    @classmethod
+    def configurable_default(cls):
+        """Returns the implementation class to be used if none is configured."""
+        raise NotImplementedError()
+
+    def initialize(self):
+        """Initialize a `Configurable` subclass instance.
+
+        Configurable classes should use `initialize` instead of `__init__`.
+        """
+
+    @classmethod
+    def configure(cls, impl, **kwargs):
+        """Sets the class to use when the base class is instantiated.
+
+        Keyword arguments will be saved and added to the arguments passed
+        to the constructor.  This can be used to set global defaults for
+        some parameters.
+        """
+        base = cls.configurable_base()
+        if isinstance(impl, (unicode, bytes_type)):
+            impl = import_object(impl)
+        if impl is not None and not issubclass(impl, cls):
+            raise ValueError("Invalid subclass of %s" % cls)
+        base.__impl_class = impl
+        base.__impl_kwargs = kwargs
+
+    @classmethod
+    def configured_class(cls):
+        """Returns the currently configured class."""
+        base = cls.configurable_base()
+        if cls.__impl_class is None:
+            base.__impl_class = cls.configurable_default()
+        return base.__impl_class
+
+
+    @classmethod
+    def _save_configuration(cls):
+        base = cls.configurable_base()
+        return (base.__impl_class, base.__impl_kwargs)
+
+    @classmethod
+    def _restore_configuration(cls, saved):
+        base = cls.configurable_base()
+        base.__impl_class = saved[0]
+        base.__impl_kwargs = saved[1]
+
+
 def doctests():
     import doctest
     return doctest.DocTestSuite()