Merge pull request #414 from MITx/kimth/xqueue_callback_blocking

Rename acquire_lock to select_for_update, add docstring

lms/djangoapps/courseware/models.py

@@ -67,7 +67,7 @@ class StudentModuleCache(object):
     """
     A cache of StudentModules for a specific student
     """
-    def __init__(self, user, descriptors, acquire_lock=False):
+    def __init__(self, user, descriptors, select_for_update=False):
         '''
         Find any StudentModule objects that are needed by any descriptor
         in descriptors. Avoids making multiple queries to the database.
@@ -77,6 +77,7 @@ class StudentModuleCache(object):
         Arguments
         user: The user for which to fetch maching StudentModules
         descriptors: An array of XModuleDescriptors.
+        select_for_update: Flag indicating whether the row should be locked until end of transaction
         '''
         if user.is_authenticated():
             module_ids = self._get_module_state_keys(descriptors) 
@@ -86,7 +87,7 @@ class StudentModuleCache(object):
             self.cache = []
             chunk_size = 500
             for id_chunk in [module_ids[i:i + chunk_size] for i in xrange(0, len(module_ids), chunk_size)]:
-                if acquire_lock:
+                if select_for_update:
                     self.cache.extend(StudentModule.objects.select_for_update().filter(
                         student=user,
                         module_state_key__in=id_chunk)
@@ -102,13 +103,14 @@ class StudentModuleCache(object):
     
     
     @classmethod
-    def cache_for_descriptor_descendents(cls, user, descriptor, depth=None, descriptor_filter=lambda descriptor: True, acquire_lock=False):
+    def cache_for_descriptor_descendents(cls, user, descriptor, depth=None, descriptor_filter=lambda descriptor: True, select_for_update=False):
         """
         descriptor: An XModuleDescriptor
         depth is the number of levels of descendent modules to load StudentModules for, in addition to
             the supplied descriptor. If depth is None, load all descendent StudentModules
         descriptor_filter is a function that accepts a descriptor and return wether the StudentModule 
             should be cached
+        select_for_update: Flag indicating whether the row should be locked until end of transaction
         """
         
         def get_child_descriptors(descriptor, depth, descriptor_filter):
@@ -128,7 +130,7 @@ class StudentModuleCache(object):
         
         descriptors = get_child_descriptors(descriptor, depth, descriptor_filter)
         
-        return StudentModuleCache(user, descriptors, acquire_lock)
+        return StudentModuleCache(user, descriptors, select_for_update)
     
     def _get_module_state_keys(self, descriptors):
         '''

lms/djangoapps/courseware/module_render.py

@@ -308,7 +308,7 @@ def xqueue_callback(request, course_id, userid, id, dispatch):
     user = User.objects.get(id=userid)
 
     student_module_cache = StudentModuleCache.cache_for_descriptor_descendents(
-        user, modulestore().get_item(id), depth=0, acquire_lock=True)
+        user, modulestore().get_item(id), depth=0, select_for_update=True)
     instance = get_module(user, request, id, student_module_cache)
     if instance is None:
         log.debug("No module {} for user {}--access denied?".format(id, user))