vm: emit {pre,post}_state_changed signals

circle/vm/models.py

@@ -10,6 +10,7 @@ from django.core import signing
 from django.db.models import (Model, ForeignKey, ManyToManyField, IntegerField,
                               DateTimeField, BooleanField, TextField,
                               CharField, permalink, Manager)
+from django.dispatch import Signal
 from django.utils import timezone
 from django.utils.translation import ugettext_lazy as _
 
@@ -33,6 +34,9 @@ ARCHITECTURES = (('x86_64', 'x86-64 (64 bit)'),
                  ('i686', 'x86 (32 bit)'))
 VNC_PORT_RANGE = (2000, 65536)  # inclusive start, exclusive end
 
+pre_state_changed = Signal(providing_args=["new_state"])
+post_state_changed = Signal(providing_args=["new_state"])
+
 
 class InstanceActiveManager(Manager):
     def get_query_set(self):
@@ -858,8 +862,15 @@ class Instance(AclBase, VirtualMachineDescModel, TimeStampedModel):
         logger.debug('Instance %s state changed '
                      '(db: %s, new: %s)',
                      self, self.state, new_state)
-        self.state = new_state
-        self.save()
+        try:
+            pre_state_changed.send(sender=self, new_state=new_state)
+        except Exception as e:
+            logger.info('Instance %s state change ignored: %s',
+                        unicode(self), unicode(e))
+        else:
+            self.state = new_state
+            self.save()
+            post_state_changed.send(sender=self, new_state=new_state)
 
 
 class InstanceActivity(ActivityModel):

circle/vm/tests/test_models.py

 from django.test import TestCase
-from ..models import InstanceTemplate
+
+from mock import Mock
+
+from ..models import (
+    InstanceTemplate, Instance, pre_state_changed, post_state_changed
+)
 
 
 class TemplateTestCase(TestCase):
+
     def test_template_creation(self):
         template = InstanceTemplate(name='My first template',
                                     access_method='ssh', )
         template.clean()
         # TODO add images & net
+
+
+class InstanceTestCase(TestCase):
+
+    def test_pre_state_changed_w_exception(self):
+        """Signal handler of pre_state_changed prevents save with Exception."""
+        def callback(sender, new_state, **kwargs):
+            if new_state == 'invalid value':
+                raise Exception()
+        pre_state_changed.connect(callback)
+        i = Instance(state='NOSTATE')
+        i.save = Mock()
+        i.state_changed('invalid value')
+        assert i.state == 'NOSTATE'
+        assert not i.save.called
+
+    def test_pre_state_changed_wo_exception(self):
+        """Signal handler of pre_state_changed allows save."""
+        mock = Mock()
+        pre_state_changed.connect(mock)
+        i = Instance(state='NOSTATE')
+        i.save = Mock()
+        i.state_changed('RUNNING')
+        assert i.state == 'RUNNING'
+        assert mock.called
+        assert i.save.called
+
+    def test_post_state_changed(self):
+        """Signal handler of post_state_changed runs."""
+        mock = Mock()
+        post_state_changed.connect(mock)
+        i = Instance(state='NOSTATE')
+        i.save = Mock()
+        i.state_changed('RUNNING')
+        assert mock.called
+        assert i.save.called
+        assert i.state == 'RUNNING'