ansible: preload built-in modules in ModuleDepScanner.

For "ansible -m setup" over a 25ms link, avoids 65 roundtrips and
reduces runtime from 5.7s to 4.1s (-28%).

For "ansible -m setup" over a simulated 250 ms link, reduces runtime
from m27.015s to 0m8.254s (-69%).

ansible_mitogen/mixins.py

@@ -313,6 +313,7 @@ class ActionModuleMixin(ansible.plugins.action.ActionBase):
         env = {}
         self._compute_environment_string(env)
 
+        self._connection._connect()
         return ansible_mitogen.planner.invoke(
             ansible_mitogen.planner.Invocation(
                 action=self,

ansible_mitogen/planner.py

@@ -181,7 +181,6 @@ class BinaryPlanner(Planner):
         return module_common._is_binary(invocation.module_source)
 
     def _grant_file_service_access(self, invocation):
-        invocation.connection._connect()
         invocation.connection.parent.call_service(
             service_name='ansible_mitogen.services.FileService',
             method_name='register',
@@ -297,7 +296,6 @@ class NewStylePlanner(ScriptPlanner):
         )
 
     def get_module_utils(self, invocation):
-        invocation.connection._connect()
         return invocation.connection.parent.call_service(
             service_name='ansible_mitogen.services.ModuleDepService',
             method_name='scan',
@@ -306,6 +304,7 @@ class NewStylePlanner(ScriptPlanner):
             module_path=invocation.module_path,
             search_path=self.get_search_path(invocation),
             builtin_path=module_common._MODULE_UTILS_PATH,
+            context=invocation.connection.context,
         )
 
     def plan(self, invocation):

ansible_mitogen/services.py

@@ -624,32 +624,50 @@ class ModuleDepService(mitogen.service.Service):
         self._file_service = file_service
         self._cache = {}
 
+    def _get_builtin_names(self, builtin_path, resolved):
+        return [
+            fullname
+            for fullname, path, is_pkg in resolved
+            if os.path.abspath(path).startswith(builtin_path)
+        ]
+
+    def _get_custom_tups(self, builtin_path, resolved):
+        return [
+            (fullname, path, is_pkg)
+            for fullname, path, is_pkg in resolved
+            if not os.path.abspath(path).startswith(builtin_path)
+        ]
+
     @mitogen.service.expose(policy=mitogen.service.AllowParents())
     @mitogen.service.arg_spec({
         'module_name': basestring,
         'module_path': basestring,
         'search_path': tuple,
         'builtin_path': basestring,
+        'context': mitogen.core.Context,
     })
-    def scan(self, module_name, module_path, search_path, builtin_path):
-        if (module_name, search_path) not in self._cache:
+    def scan(self, module_name, module_path, search_path, builtin_path, context):
+        key = (module_name, search_path)
+        if key not in self._cache:
             resolved = ansible_mitogen.module_finder.scan(
                 module_name=module_name,
                 module_path=module_path,
                 search_path=tuple(search_path) + (builtin_path,),
             )
             builtin_path = os.path.abspath(builtin_path)
-            filtered = [
-                (fullname, path, is_pkg)
-                for fullname, path, is_pkg in resolved
-                if not os.path.abspath(path).startswith(builtin_path)
-            ]
-            self._cache[module_name, search_path] = filtered
+            builtin = self._get_builtin_names(builtin_path, resolved)
+            custom = self._get_custom_tups(builtin_path, resolved)
+            self._cache[key] = {
+                'builtin': builtin,
+                'custom': custom,
+            }
 
             # Grant FileService access to paths in here to avoid another 2 IPCs
             # from WorkerProcess.
             self._file_service.register(path=module_path)
-            for fullname, path, is_pkg in filtered:
+            for fullname, path, is_pkg in custom:
                 self._file_service.register(path=path)
 
-        return self._cache[module_name, search_path]
+        for name in self._cache[key]['builtin']:
+            self.router.responder.forward_module(context, name)
+        return self._cache[key]['custom']