I am seeing a release unlocked lock error appear occasionally in the logs for

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Asked: June 4, 20262026-06-04T07:05:30+00:00 2026-06-04T07:05:30+00:00

I am seeing a release unlocked lock error appear occasionally in the logs for

0

I am seeing a “release unlocked lock” error appear occasionally in the logs for my app on Google App Engine (gqueues) and cannot figure out why (complete stack trace below). Does anyone know why this error would occur?

Interestingly the app is on python 2.7 with threadsafe=NO, so it seems weird that there would be any locking going on at all, or locking errors.

The backstory: GQueues was on python2.5, and at the beginning of April I migrated it to 2.7 and set threadsafe=True. Everything worked fine for a week. Then on the morning of April 9 the entire app was inaccessible, spitting out 500 errors. It kept spawning new server instances that would have latencies of over 30 seconds. I noticed in my logs I saw the error “Cannot unlock an unlocked lock”. I did not add any locking mechanisms to my code during the migration, so I assumed this was app engine’s locking that the error was referring to. Anyway, I rolled back my app to the previous version that was still on Python 2.5 and everything started working again.

Later in April AppEngine Downtime Notify revealed that there was an issue on their end on April 9 that was causing problems with python 2.7 apps.
https://groups.google.com/d/topic/google-appengine-downtime-notify/QL8TmRn6Ay4/discussion

I followed up with Christina Ilvento from Google and she thought it should be fine to move back to Python 2.7 now and turn threadsafe=True. I migrated back to 2.7 but left threadsafe=False, thinking that I would give it a couple weeks to make sure everything worked well on 2.7 before turning on threading again (which I assumed was causing the problem). Everything worked fine for a few weeks, but now I’m seeing this “release unlocked lock” error even with threading disabled. Does anyone know what’s going on here?

Christina suggested I post here and the App Engine team would follow up.

release unlocked lock
Traceback (most recent call last):
  File "/base/python27_runtime/python27_lib/versions/third_party/webapp2-2.3/webapp2.py", line 545, in dispatch
    return method(*args, **kwargs)
  File "/base/data/home/apps/s~gqueues-hrd/gq3-7-5.358902352474055782/controllers/util.py", line 69, in check_login
    handler_method(self, *args)
  File "/base/data/home/apps/s~gqueues-hrd/gq3-7-5.358902352474055782/controllers/main.py", line 297, in get
    self.generate('main.html', template_values)
  File "/base/data/home/apps/s~gqueues-hrd/gq3-7-5.358902352474055782/controllers/baserequest.py", line 257, in generate
    self.response.out.write(template.render(path, values))
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/ext/webapp/template.py", line 92, in render
    return t.render(Context(template_dict))
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/ext/webapp/template.py", line 172, in wrap_render
    return orig_render(context)
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/_internal/django/template/__init__.py", line 173, in render
    return self._render(context)
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/_internal/django/template/__init__.py", line 167, in _render
    return self.nodelist.render(context)
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/_internal/django/template/__init__.py", line 794, in render
    bits.append(self.render_node(node, context))
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/_internal/django/template/__init__.py", line 807, in render_node
    return node.render(context)
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/_internal/django/template/loader_tags.py", line 139, in render
    return self.template.render(context)
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/_internal/django/template/__init__.py", line 173, in render
    return self._render(context)
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/_internal/django/template/__init__.py", line 167, in _render
    return self.nodelist.render(context)
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/_internal/django/template/__init__.py", line 794, in render
    bits.append(self.render_node(node, context))
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/_internal/django/template/__init__.py", line 807, in render_node
    return node.render(context)
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/_internal/django/template/defaulttags.py", line 173, in render
    nodelist.append(node.render(context))
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/_internal/django/template/defaulttags.py", line 257, in render
    return self.nodelist_true.render(context)
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/_internal/django/template/__init__.py", line 794, in render
    bits.append(self.render_node(node, context))
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/_internal/django/template/__init__.py", line 807, in render_node
    return node.render(context)
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/_internal/django/template/loader_tags.py", line 139, in render
    return self.template.render(context)
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/_internal/django/template/__init__.py", line 173, in render
    return self._render(context)
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/_internal/django/template/__init__.py", line 167, in _render
    return self.nodelist.render(context)
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/_internal/django/template/__init__.py", line 794, in render
    bits.append(self.render_node(node, context))
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/_internal/django/template/__init__.py", line 807, in render_node
    return node.render(context)
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/_internal/django/template/loader_tags.py", line 139, in render
    return self.template.render(context)
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/_internal/django/template/__init__.py", line 173, in render
    return self._render(context)
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/_internal/django/template/__init__.py", line 167, in _render
    return self.nodelist.render(context)
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/_internal/django/template/__init__.py", line 794, in render
    bits.append(self.render_node(node, context))
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/_internal/django/template/__init__.py", line 807, in render_node
    return node.render(context)
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/_internal/django/template/defaulttags.py", line 173, in render
    nodelist.append(node.render(context))
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/_internal/django/template/loader_tags.py", line 139, in render
    return self.template.render(context)
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/_internal/django/template/__init__.py", line 173, in render
    return self._render(context)
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/_internal/django/template/__init__.py", line 167, in _render
    return self.nodelist.render(context)
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/_internal/django/template/__init__.py", line 794, in render
    bits.append(self.render_node(node, context))
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/_internal/django/template/__init__.py", line 807, in render_node
    return node.render(context)
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/_internal/django/template/loader_tags.py", line 139, in render
    return self.template.render(context)
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/_internal/django/template/__init__.py", line 173, in render
    return self._render(context)
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/_internal/django/template/__init__.py", line 167, in _render
    return self.nodelist.render(context)
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/_internal/django/template/__init__.py", line 794, in render
    bits.append(self.render_node(node, context))
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/_internal/django/template/__init__.py", line 807, in render_node
    return node.render(context)
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/_internal/django/template/defaulttags.py", line 136, in render
    values = list(values)
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/ext/db/__init__.py", line 2312, in next
    return self.__model_class.from_entity(self.__iterator.next())
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/datastore/datastore_query.py", line 2809, in next
    next_batch = self.__batcher.next()
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/datastore/datastore_query.py", line 2671, in next
    return self.next_batch(self.AT_LEAST_ONE)
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/datastore/datastore_query.py", line 2708, in next_batch
    batch = self.__next_batch.get_result()
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/api/apiproxy_stub_map.py", line 592, in get_result
    return self.__get_result_hook(self)
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/datastore/datastore_query.py", line 2450, in __query_result_hook
    self._batch_shared.conn.check_rpc_success(rpc)
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/datastore/datastore_rpc.py",

UPDATE:
Here is a complete backtrace for one of the errors

46.231.181.199 - sandra.martin [15/May/2012:03:28:44 -0700] "POST /items/ HTTP/1.1" 500 1306 "http://www.gqueues.com/main?q=ag1zfmdxdWV1ZXMtaHJkciILEgdBY2NvdW50GL-psgYMCxILU2hhcmVkUXVldWUYkU4M";;;; "Mozilla/5.0 (Windows NT 6.1; rv:12.0) Gecko/20100101 Firefox/12.0" "www.gqueues.com" ms=59858 cpu_ms=154948 api_cpu_ms=112433 cpm_usd=4.305925 instance=00c61b117cfbf1818fa4b0f779eacc7f4a9030
D 2012-05-15 05:27:45.121
postAction: reorder
E 2012-05-15 05:28:44.714
release unlocked lock
Traceback (most recent call last):
  File "/base/python27_runtime/python27_lib/versions/third_party/webapp2-2.3/webapp2.py", line 545, in dispatch
    return method(*args, **kwargs)
  File "/base/data/home/apps/s~gqueues-hrd/gq3-7-5.358902352474055782/controllers/util.py", line 139, in check_login
    handler_method(self, *args)
  File "/base/data/home/apps/s~gqueues-hrd/gq3-7-5.358902352474055782/controllers/items.py", line 371, in post
    self.reorder()
  File "/base/data/home/apps/s~gqueues-hrd/gq3-7-5.358902352474055782/controllers/items.py", line 856, in reorder
    QueueSyncHandler.syncQueueViewers(clientId, itemQueue)
  File "/base/data/home/apps/s~gqueues-hrd/gq3-7-5.358902352474055782/controllers/queuesync.py", line 197, in syncQueueViewers
    jsonObj['items']        = util.getJSONItems(queueItems, filter, queueViewer.type, accountObj)
  File "/base/data/home/apps/s~gqueues-hrd/gq3-7-5.358902352474055782/controllers/util.py", line 1536, in getJSONItems
    jsonItem['subitems'] = getJSONItems(subItems, filter, type, accountObj, assignmentCompleted=assignmentCompleted, accountEmail=accountEmail)
  File "/base/data/home/apps/s~gqueues-hrd/gq3-7-5.358902352474055782/controllers/util.py", line 1536, in getJSONItems
    jsonItem['subitems'] = getJSONItems(subItems, filter, type, accountObj, assignmentCompleted=assignmentCompleted, accountEmail=accountEmail)
  File "/base/data/home/apps/s~gqueues-hrd/gq3-7-5.358902352474055782/controllers/util.py", line 1536, in getJSONItems
    jsonItem['subitems'] = getJSONItems(subItems, filter, type, accountObj, assignmentCompleted=assignmentCompleted, accountEmail=accountEmail)
  File "/base/data/home/apps/s~gqueues-hrd/gq3-7-5.358902352474055782/controllers/util.py", line 1481, in getJSONItems
    if item.hasAssignments():
  File "/base/data/home/apps/s~gqueues-hrd/gq3-7-5.358902352474055782/models.py", line 1512, in hasAssignments
    itemAssignments = Assignment.all(keys_only=True).filter('item =', self).fetch(1)
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/ext/db/__init__.py", line 2143, in fetch
    return list(self.run(limit=limit, offset=offset, **kwargs))
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/datastore/datastore_query.py", line 2809, in next
    next_batch = self.__batcher.next()
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/datastore/datastore_query.py", line 2671, in next
    return self.next_batch(self.AT_LEAST_ONE)
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/datastore/datastore_query.py", line 2708, in next_batch
    batch = self.__next_batch.get_result()
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/api/apiproxy_stub_map.py", line 592, in get_result
    return self.__get_result_hook(self)
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/datastore/datastore_query.py", line 2450, in __query_result_hook
    self._batch_shared.conn.check_rpc_success(rpc)
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/datastore/datastore_rpc.py", line 1206, in check_rpc_success
    rpc.wait()
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/api/apiproxy_stub_map.py", line 533, in wait
    self.__rpc.Wait()
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/api/apiproxy_rpc.py", line 119, in Wait
    rpc_completed = self._WaitImpl()
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/runtime/apiproxy.py", line 134, in _WaitImpl
    self.__done_event.wait()
  File "/base/python27_runtime/python27_dist/lib/python2.7/threading.py", line 407, in wait
    self.__cond.release()
error: release unlocked lock

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1 Answer

Editorial Team · Answer 1 · 2026-06-04T07:05:31+00:00

Thanks for the report. We (the GAE python team) are aware of this bug. What’s probably happening is that your handler is probably hitting the request deadline and running into a problem we warn about at https://developers.google.com/appengine/docs/python/runtime#The_Request_Timer.

Can you check a couple of things for me:
1. The exception trace appears to be incomplete. If possible, can you post a full backtrace.
2. Can you check the request times for your requests that are hitting this (in the logs) and post them here.

EDIT: The warning on the page I linked to was posted recently.

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I am seeing a release unlocked lock error appear occasionally in the logs for

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