Fix queue handling to remove the dependency from repobuild, and have a cancel method

data/queue.py

@@ -82,10 +82,19 @@ class WorkQueue(object):
     self._reporter(self._currently_processing, running_count,
                    running_count + available_not_running_count)
 
+  def has_retries_remaining(self, item_id):
+    """ Returns whether the queue item with the given id has any retries remaining. If the
+        queue item does not exist, returns False. """
+    with self._transaction_factory(db):
+      try:
+        return QueueItem.get(id=item_id).retries_remaining > 0
+      except QueueItem.DoesNotExist:
+        return False
+
   def put(self, canonical_name_list, message, available_after=0, retries_remaining=5):
     """
     Put an item, if it shouldn't be processed for some number of seconds,
-    specify that amount as available_after.
+    specify that amount as available_after. Returns the ID of the queue item added.
     """
 
     params = {
@@ -98,7 +107,7 @@ class WorkQueue(object):
     params['available_after'] = available_date
 
     with self._transaction_factory(db):
-      return QueueItem.create(**params)
+      return str(QueueItem.create(**params).id)
 
   def get(self, processing_time=300):
     """
@@ -141,10 +150,32 @@ class WorkQueue(object):
     # Return a view of the queue item rather than an active db object
     return item
 
+  def cancel(self, item_id):
+    """ Attempts to cancel the queue item with the given ID from the queue. Returns true on success
+        and false if the queue item could not be canceled. A queue item can only be canceled if
+        if is available and has retries remaining.
+    """
+
+    with self._transaction_factory(db):
+      # Load the build queue item for update.
+      try:
+        queue_item = db_for_update(QueueItem.select()
+                                            .where(QueueItem.id == item_id)).get()
+      except QueueItem.DoesNotExist:
+        return False
+
+      # Check the queue item.
+      if not queue_item.available or queue_item.retries_remaining == 0:
+        return False
+
+      # Delete the queue item.
+      queue_item.delete_instance(recursive=True)
+      return True
+
   def complete(self, completed_item):
     with self._transaction_factory(db):
       completed_item_obj = self._item_by_id_for_update(completed_item.id)
-      completed_item_obj.delete_instance()
+      completed_item_obj.delete_instance(recursive=True)
       self._currently_processing = False
 
   def incomplete(self, incomplete_item, retry_after=300, restore_retry=False):