add lib for subliminal and set non-intrusive default ionice.

libs/stevedore/extension.py

@@ -0,0 +1,275 @@
+"""ExtensionManager
+"""
+
+import pkg_resources
+
+import logging
+
+
+LOG = logging.getLogger(__name__)
+
+
+class Extension(object):
+    """Book-keeping object for tracking extensions.
+
+    The arguments passed to the constructor are saved as attributes of
+    the instance using the same names, and can be accessed by the
+    callables passed to :meth:`map` or when iterating over an
+    :class:`ExtensionManager` directly.
+
+    :param name: The entry point name.
+    :type name: str
+    :param entry_point: The EntryPoint instance returned by
+        :mod:`pkg_resources`.
+    :type entry_point: EntryPoint
+    :param plugin: The value returned by entry_point.load()
+    :param obj: The object returned by ``plugin(*args, **kwds)`` if the
+                manager invoked the extension on load.
+
+    """
+
+    def __init__(self, name, entry_point, plugin, obj):
+        self.name = name
+        self.entry_point = entry_point
+        self.plugin = plugin
+        self.obj = obj
+
+    @property
+    def entry_point_target(self):
+        """The module and attribute referenced by this extension's entry_point.
+
+        :return: A string representation of the target of the entry point in
+            'dotted.module:object' format.
+        """
+        return '%s:%s' % (self.entry_point.module_name,
+                          self.entry_point.attrs[0])
+
+
+class ExtensionManager(object):
+    """Base class for all of the other managers.
+
+    :param namespace: The namespace for the entry points.
+    :type namespace: str
+    :param invoke_on_load: Boolean controlling whether to invoke the
+        object returned by the entry point after the driver is loaded.
+    :type invoke_on_load: bool
+    :param invoke_args: Positional arguments to pass when invoking
+        the object returned by the entry point. Only used if invoke_on_load
+        is True.
+    :type invoke_args: tuple
+    :param invoke_kwds: Named arguments to pass when invoking
+        the object returned by the entry point. Only used if invoke_on_load
+        is True.
+    :type invoke_kwds: dict
+    :param propagate_map_exceptions: Boolean controlling whether exceptions
+        are propagated up through the map call or whether they are logged and
+        then ignored
+    :type propagate_map_exceptions: bool
+    :param on_load_failure_callback: Callback function that will be called when
+        a entrypoint can not be loaded. The arguments that will be provided
+        when this is called (when an entrypoint fails to load) are
+        (manager, entrypoint, exception)
+    :type on_load_failure_callback: function
+    :param verify_requirements: Use setuptools to enforce the
+        dependencies of the plugin(s) being loaded. Defaults to False.
+    :type verify_requirements: bool
+    """
+
+    def __init__(self, namespace,
+                 invoke_on_load=False,
+                 invoke_args=(),
+                 invoke_kwds={},
+                 propagate_map_exceptions=False,
+                 on_load_failure_callback=None,
+                 verify_requirements=False):
+        self._init_attributes(
+            namespace,
+            propagate_map_exceptions=propagate_map_exceptions,
+            on_load_failure_callback=on_load_failure_callback)
+        extensions = self._load_plugins(invoke_on_load,
+                                        invoke_args,
+                                        invoke_kwds,
+                                        verify_requirements)
+        self._init_plugins(extensions)
+
+    @classmethod
+    def make_test_instance(cls, extensions, namespace='TESTING',
+                           propagate_map_exceptions=False,
+                           on_load_failure_callback=None,
+                           verify_requirements=False):
+        """Construct a test ExtensionManager
+
+        Test instances are passed a list of extensions to work from rather
+        than loading them from entry points.
+
+        :param extensions: Pre-configured Extension instances to use
+        :type extensions: list of :class:`~stevedore.extension.Extension`
+        :param namespace: The namespace for the manager; used only for
+            identification since the extensions are passed in.
+        :type namespace: str
+        :param propagate_map_exceptions: When calling map, controls whether
+            exceptions are propagated up through the map call or whether they
+            are logged and then ignored
+        :type propagate_map_exceptions: bool
+        :param on_load_failure_callback: Callback function that will
+            be called when a entrypoint can not be loaded. The
+            arguments that will be provided when this is called (when
+            an entrypoint fails to load) are (manager, entrypoint,
+            exception)
+        :type on_load_failure_callback: function
+        :param verify_requirements: Use setuptools to enforce the
+            dependencies of the plugin(s) being loaded. Defaults to False.
+        :type verify_requirements: bool
+        :return: The manager instance, initialized for testing
+
+        """
+
+        o = cls.__new__(cls)
+        o._init_attributes(namespace,
+                           propagate_map_exceptions=propagate_map_exceptions,
+                           on_load_failure_callback=on_load_failure_callback)
+        o._init_plugins(extensions)
+        return o
+
+    def _init_attributes(self, namespace, propagate_map_exceptions=False,
+                         on_load_failure_callback=None):
+        self.namespace = namespace
+        self.propagate_map_exceptions = propagate_map_exceptions
+        self._on_load_failure_callback = on_load_failure_callback
+
+    def _init_plugins(self, extensions):
+        self.extensions = extensions
+        self._extensions_by_name = None
+
+    ENTRY_POINT_CACHE = {}
+
+    def _find_entry_points(self, namespace):
+        if namespace not in self.ENTRY_POINT_CACHE:
+            eps = list(pkg_resources.iter_entry_points(namespace))
+            self.ENTRY_POINT_CACHE[namespace] = eps
+        return self.ENTRY_POINT_CACHE[namespace]
+
+    def _load_plugins(self, invoke_on_load, invoke_args, invoke_kwds,
+                      verify_requirements):
+        extensions = []
+        for ep in self._find_entry_points(self.namespace):
+            LOG.debug('found extension %r', ep)
+            try:
+                ext = self._load_one_plugin(ep,
+                                            invoke_on_load,
+                                            invoke_args,
+                                            invoke_kwds,
+                                            verify_requirements,
+                                            )
+                if ext:
+                    extensions.append(ext)
+            except (KeyboardInterrupt, AssertionError):
+                raise
+            except Exception as err:
+                LOG.error('Could not load %r: %s', ep.name, err)
+                LOG.exception(err)
+                if self._on_load_failure_callback is not None:
+                    self._on_load_failure_callback(self, ep, err)
+        return extensions
+
+    def _load_one_plugin(self, ep, invoke_on_load, invoke_args, invoke_kwds,
+                         verify_requirements):
+        plugin = ep.load(require=verify_requirements)
+        if invoke_on_load:
+            obj = plugin(*invoke_args, **invoke_kwds)
+        else:
+            obj = None
+        return Extension(ep.name, ep, plugin, obj)
+
+    def names(self):
+        "Returns the names of the discovered extensions"
+        # We want to return the names of the extensions in the order
+        # they would be used by map(), since some subclasses change
+        # that order.
+        return [e.name for e in self.extensions]
+
+    def map(self, func, *args, **kwds):
+        """Iterate over the extensions invoking func() for each.
+
+        The signature for func() should be::
+
+            def func(ext, *args, **kwds):
+                pass
+
+        The first argument to func(), 'ext', is the
+        :class:`~stevedore.extension.Extension` instance.
+
+        Exceptions raised from within func() are propagated up and
+        processing stopped if self.propagate_map_exceptions is True,
+        otherwise they are logged and ignored.
+
+        :param func: Callable to invoke for each extension.
+        :param args: Variable arguments to pass to func()
+        :param kwds: Keyword arguments to pass to func()
+        :returns: List of values returned from func()
+        """
+        if not self.extensions:
+            # FIXME: Use a more specific exception class here.
+            raise RuntimeError('No %s extensions found' % self.namespace)
+        response = []
+        for e in self.extensions:
+            self._invoke_one_plugin(response.append, func, e, args, kwds)
+        return response
+
+    @staticmethod
+    def _call_extension_method(extension, method_name, *args, **kwds):
+        return getattr(extension.obj, method_name)(*args, **kwds)
+
+    def map_method(self, method_name, *args, **kwds):
+        """Iterate over the extensions invoking a method by name.
+
+        This is equivalent of using :meth:`map` with func set to
+        `lambda x: x.obj.method_name()`
+        while being more convenient.
+
+        Exceptions raised from within the called method are propagated up
+        and processing stopped if self.propagate_map_exceptions is True,
+        otherwise they are logged and ignored.
+
+        .. versionadded:: 0.12
+
+        :param method_name: The extension method name
+                            to call for each extension.
+        :param args: Variable arguments to pass to method
+        :param kwds: Keyword arguments to pass to method
+        :returns: List of values returned from methods
+        """
+        return self.map(self._call_extension_method,
+                        method_name, *args, **kwds)
+
+    def _invoke_one_plugin(self, response_callback, func, e, args, kwds):
+        try:
+            response_callback(func(e, *args, **kwds))
+        except Exception as err:
+            if self.propagate_map_exceptions:
+                raise
+            else:
+                LOG.error('error calling %r: %s', e.name, err)
+                LOG.exception(err)
+
+    def __iter__(self):
+        """Produce iterator for the manager.
+
+        Iterating over an ExtensionManager produces the :class:`Extension`
+        instances in the order they would be invoked.
+        """
+        return iter(self.extensions)
+
+    def __getitem__(self, name):
+        """Return the named extension.
+
+        Accessing an ExtensionManager as a dictionary (``em['name']``)
+        produces the :class:`Extension` instance with the
+        specified name.
+        """
+        if self._extensions_by_name is None:
+            d = {}
+            for e in self.extensions:
+                d[e.name] = e
+            self._extensions_by_name = d
+        return self._extensions_by_name[name]