Initial commit of the lock manager

apps/lock_manager/models.py

@@ -0,0 +1,54 @@
+import datetime
+
+from django.db import models
+from django.utils.translation import ugettext_lazy as _
+from django.db.utils import IntegrityError
+from django.db import transaction
+
+
+class LockError(Exception):
+    pass
+
+class LockManager(models.Manager):
+    @transaction.commit_manually
+    def acquire_lock(self, name):
+        lock = self.model(name=name)
+        try:
+            lock.save(force_insert=True)
+        except IntegrityError:
+            transaction.rollback()
+            # There is already an existing lock
+            # Check it's expiration date and if expired delete it and 
+            # re-create it
+            lock = Lock.objects.get(name=name)
+            if datetime.datetime.now() > lock.creation_datetime + datetime.timedelta(seconds=lock.expiration):
+                release_lock(self)
+                lock.save()
+            else:
+                raise LockError('Unable to acquire lock')
+        else:
+            transaction.commit()
+        
+    @transaction.commit_manually
+    def release_lock(self, name):
+        lock = Lock.objects.get(name=name)
+        lock.delete()
+        transaction.commit()
+
+class Lock(models.Model):
+    creation_datetime = models.DateTimeField(verbose_name=_(u'creation datetime'))
+    expiration_time = models.IntegerField(default=3600, verbose_name=_(u'expiration time'))
+    name = models.CharField(max_length=32, verbose_name=_(u'name'), unique=True)
+    
+    objects = LockManager()
+    
+    def __unicode__(self):
+        return self.name
+        
+    def save(self, *args, **kwargs):
+        self.creation_datetime = datetime.datetime.now()
+        super(Lock, self).save(*args, **kwargs)
+        
+    class Meta:
+        verbose_name = _(u'lock')
+        verbose_name_plural = _(u'locks')

apps/lock_manager/tests.py

@@ -0,0 +1,16 @@
+"""
+This file demonstrates writing tests using the unittest module. These will pass
+when you run "manage.py test".
+
+Replace this with more appropriate tests for your application.
+"""
+
+from django.test import TestCase
+
+
+class SimpleTest(TestCase):
+    def test_basic_addition(self):
+        """
+        Tests that 1 + 1 always equals 2.
+        """
+        self.assertEqual(1 + 1, 2)

apps/lock_manager/views.py

@@ -0,0 +1 @@
+# Create your views here.

settings.py

@@ -129,6 +129,7 @@ INSTALLED_APPS = (
     'project_tools',
     'smart_settings',
     'navigation',
+    'lock_manager',
     'web_theme',
     'common',
     'metadata',