Make tutor considerably faster

Tutor was making many calls to iter_installed (~100 on my machine with a
dozen installed plugins). Turns out it's useless to cache Plugin and
Renderer instances, as the config keeps changing all the time. Instead,
we cache the list of installed plugins, which does not change in the
course of a single run.

On my machine this speeds up `tutor config save` by 5x, going from 7.5s
to 1.3s.

bin/main.py

@@ -12,7 +12,7 @@ for plugin_name in [
     "xqueue",
 ]:
     try:
-        OfficialPlugin.INSTALLED.append(OfficialPlugin(plugin_name))
+        OfficialPlugin.load(plugin_name)
     except ImportError:
         pass
 

tests/test_plugins.py

@@ -20,12 +20,11 @@ class PluginsTests(unittest.TestCase):
         self.assertFalse(plugins.is_installed("dummy"))
 
     @patch.object(plugins.DictPlugin, "iter_installed", return_value=[])
-    def test_extra_installed(self, _dict_plugin_iter_installed):
-        plugin1 = plugins.BasePlugin("plugin1", None)
-        plugin2 = plugins.BasePlugin("plugin2", None)
-
-        plugins.OfficialPlugin.INSTALLED.append(plugin1)
-        plugins.OfficialPlugin.INSTALLED.append(plugin2)
+    def test_official_plugins(self, _dict_plugin_iter_installed):
+        with patch.object(plugins.importlib, "import_module", return_value=42):
+            plugin1 = plugins.OfficialPlugin.load("plugin1")
+        with patch.object(plugins.importlib, "import_module", return_value=43):
+            plugin2 = plugins.OfficialPlugin.load("plugin2")
         with patch.object(
             plugins.EntrypointPlugin, "iter_installed", return_value=[plugin1],
         ):

tutor/env.py

@@ -18,20 +18,16 @@ BIN_FILE_EXTENSIONS = [".ico", ".jpg", ".png", ".ttf", ".woff", ".woff2"]
 
 
 class Renderer:
-    INSTANCE = None
-
     @classmethod
     def instance(cls, config):
-        if cls.INSTANCE is None or cls.INSTANCE.config != config:
-            # Load template roots: these are required to be able to use
-            # {% include .. %} directives
-            template_roots = [TEMPLATES_ROOT]
-            for plugin in plugins.iter_enabled(config):
-                if plugin.templates_root:
-                    template_roots.append(plugin.templates_root)
+        # Load template roots: these are required to be able to use
+        # {% include .. %} directives
+        template_roots = [TEMPLATES_ROOT]
+        for plugin in plugins.iter_enabled(config):
+            if plugin.templates_root:
+                template_roots.append(plugin.templates_root)
 
-            cls.INSTANCE = cls(config, template_roots, ignore_folders=["partials"])
-        return cls.INSTANCE
+        return cls(config, template_roots, ignore_folders=["partials"])
 
     @classmethod
     def reset(cls):

tutor/plugins.py

@@ -47,6 +47,9 @@ class BasePlugin:
     `command` (click.Command): if a plugin exposes a `command` attribute, users will be able to run it from the command line as `tutor pluginname`.
     """
 
+    INSTALLED = []
+    _IS_LOADED = False
+
     def __init__(self, name, obj):
         self.name = name
         self.config = get_callable_attr(obj, "config", {})
@@ -79,6 +82,14 @@ class BasePlugin:
 
     @classmethod
     def iter_installed(cls):
+        if not cls._IS_LOADED:
+            for plugin in cls.iter_load():
+                cls.INSTALLED.append(plugin)
+            cls._IS_LOADED = True
+        yield from cls.INSTALLED
+
+    @classmethod
+    def iter_load(cls):
         raise NotImplementedError
 
 
@@ -101,19 +112,22 @@ class EntrypointPlugin(BasePlugin):
         return self.entrypoint.dist.version
 
     @classmethod
-    def iter_installed(cls):
+    def iter_load(cls):
         for entrypoint in pkg_resources.iter_entry_points(cls.ENTRYPOINT):
             yield cls(entrypoint)
 
 
 class OfficialPlugin(BasePlugin):
     """
-    Official plugins have a "plugin" module which exposes a __version__
-    attribute.
-    Official plugins should be manually added to INSTALLED.
+    Official plugins have a "plugin" module which exposes a __version__ attribute.
+    Official plugins should be manually added by calling `OfficialPlugin.load()`.
     """
 
-    INSTALLED = []
+    @classmethod
+    def load(cls, name):
+        plugin = cls(name)
+        cls.INSTALLED.append(plugin)
+        return plugin
 
     def __init__(self, name):
         self.module = importlib.import_module("tutor{}.plugin".format(name))
@@ -124,8 +138,8 @@ class OfficialPlugin(BasePlugin):
         return self.module.__version__
 
     @classmethod
-    def iter_installed(cls):
-        yield from cls.INSTALLED
+    def iter_load(cls):
+        yield from []
 
 
 class DictPlugin(BasePlugin):
@@ -145,7 +159,7 @@ class DictPlugin(BasePlugin):
         return self._version
 
     @classmethod
-    def iter_installed(cls):
+    def iter_load(cls):
         for path in glob(os.path.join(cls.ROOT, "*.yml")):
             with open(path) as f:
                 data = serialize.load(f)
@@ -162,8 +176,7 @@ class DictPlugin(BasePlugin):
 
 
 class Plugins:
-
-    INSTANCE = None
+    PLUGIN_CLASSES = [OfficialPlugin, EntrypointPlugin, DictPlugin]
 
     def __init__(self, config):
         self.config = deepcopy(config)
@@ -184,23 +197,17 @@ class Plugins:
 
     @classmethod
     def clear(cls):
-        cls.INSTANCE = None
-        OfficialPlugin.INSTALLED.clear()
-
-    @classmethod
-    def instance(cls, config):
-        if cls.INSTANCE is None or cls.INSTANCE.config != config:
-            cls.INSTANCE = cls(config)
-        return cls.INSTANCE
+        for PluginClass in cls.PLUGIN_CLASSES:
+            PluginClass.INSTALLED.clear()
 
     @classmethod
     def iter_installed(cls):
         """
-        Iterate on all installed plugins. Plugins are deduplicated by name.
+        Iterate on all installed plugins. Plugins are deduplicated by name. The list of installed plugins is cached to
+        prevent too many re-computations, which happens a lot.
         """
-        classes = [OfficialPlugin, EntrypointPlugin, DictPlugin]
         installed_plugin_names = set()
-        for PluginClass in classes:
+        for PluginClass in cls.PLUGIN_CLASSES:
             for plugin in PluginClass.iter_installed():
                 if plugin.name not in installed_plugin_names:
                     installed_plugin_names.add(plugin.name)
@@ -252,7 +259,7 @@ def enable(config, name):
 
 def disable(config, name):
     fmt.echo_info("Disabling plugin {}...".format(name))
-    for plugin in Plugins.instance(config).iter_enabled():
+    for plugin in Plugins(config).iter_enabled():
         if name == plugin.name:
             # Remove "set" config entries
             for key, value in plugin.config_set.items():
@@ -265,7 +272,7 @@ def disable(config, name):
 
 
 def iter_enabled(config):
-    yield from Plugins.instance(config).iter_enabled()
+    yield from Plugins(config).iter_enabled()
 
 
 def is_enabled(config, name):
@@ -273,8 +280,8 @@ def is_enabled(config, name):
 
 
 def iter_patches(config, name):
-    yield from Plugins.instance(config).iter_patches(name)
+    yield from Plugins(config).iter_patches(name)
 
 
 def iter_hooks(config, hook_name):
-    yield from Plugins.instance(config).iter_hooks(hook_name)
+    yield from Plugins(config).iter_hooks(hook_name)