startup: Handle frontend and backend failures

mopidy/backend.py

@@ -58,6 +58,10 @@ class Backend(object):
     def has_playlists(self):
         return self.playlists is not None
 
+    def ping(self):
+        """Called to check if the actor is still alive."""
+        return True
+
 
 class LibraryProvider(object):
 

mopidy/commands.py

@@ -2,6 +2,7 @@ from __future__ import absolute_import, print_function, unicode_literals
 
 import argparse
 import collections
+import contextlib
 import logging
 import os
 import sys
@@ -232,6 +233,23 @@ class Command(object):
         raise NotImplementedError
 
 
+@contextlib.contextmanager
+def _actor_error_handling(name):
+    try:
+        yield
+    except exceptions.BackendError as exc:
+        logger.error(
+            'Backend (%s) initialization error: %s', name, exc.message)
+    except exceptions.FrontendError as exc:
+        logger.error(
+            'Frontend (%s) initialization error: %s', name, exc.message)
+    except exceptions.MixerError as exc:
+        logger.error(
+            'Mixer (%s) initialization error: %s', name, exc.message)
+    except Exception:
+        logger.exception('Got un-handled exception from %s', name)
+
+
 # TODO: move out of this utility class
 class RootCommand(Command):
 
@@ -328,22 +346,14 @@ class RootCommand(Command):
 
     def start_mixer(self, config, mixer_class):
         logger.info('Starting Mopidy mixer: %s', mixer_class.__name__)
-        mixer = None
-
-        try:
+        with _actor_error_handling(mixer_class.__name__):
             mixer = mixer_class.start(config=config).proxy()
-            mixer.ping().get()
-        except exceptions.MixerError as exc:
-            logger.error('Mixer (%s) initialization error: %s',
-                         mixer_class.__name__, exc.message)
-        except pykka.ActorDeadError as exc:
-            mixer = None
-            logger.error('Mixer actor died: %s', exc)
-        except Exception:
-            logger.exception('Mixer (%s) initialization exception:',
-                             mixer_class.__name__)
-
-        return mixer
+            try:
+                mixer.ping().get()
+                return mixer
+            except pykka.ActorDeadError as exc:
+                logger.error('Actor died: %s', exc)
+        return None
 
     def configure_mixer(self, config, mixer):
         volume = config['audio']['mixer_volume']
@@ -364,16 +374,19 @@ class RootCommand(Command):
 
         backends = []
         for backend_class in backend_classes:
-            try:
+            with _actor_error_handling(backend_class.__name__):
                 with timer.time_logger(backend_class.__name__):
                     backend = backend_class.start(
                         config=config, audio=audio).proxy()
-                backends.append(backend)
-            except exceptions.BackendError as exc:
-                logger.error(
-                    'Backend (%s) initialization error: %s',
-                    backend_class.__name__, exc.message)
-                raise
+                    backends.append(backend)
+
+        # Block until all on_starts have finished, letting them run in parallel
+        for backend in backends[:]:
+            try:
+                backend.ping().get()
+            except pykka.ActorDeadError as exc:
+                backends.remove(backend)
+                logger.error('Actor died: %s', exc)
 
         return backends
 
@@ -388,14 +401,9 @@ class RootCommand(Command):
             ', '.join(f.__name__ for f in frontend_classes) or 'none')
 
         for frontend_class in frontend_classes:
-            try:
+            with _actor_error_handling(frontend_class.__name__):
                 with timer.time_logger(frontend_class.__name__):
                     frontend_class.start(config=config, core=core)
-            except exceptions.FrontendError as exc:
-                logger.error(
-                    'Frontend (%s) initialization error: %s',
-                    frontend_class.__name__, exc.message)
-                raise
 
     def stop_frontends(self, frontend_classes):
         logger.info('Stopping Mopidy frontends')