Hello, while it is not certain to be the case it appears likely that has to
do with threading. As this is a specific technical question the best way to
get it answered would be to post it on Stack Overflow
<https://stackoverflow.com/> using one of the tags
<https://cloud.google.com/support/docs/stackexchange> monitored by our
community technical support team. Be sure to include the code you believe
this error originates from and the full error traces. Once that's done you
should post a link to it here so other posters can help answer it.
On Thursday, July 27, 2017 at 12:08:49 PM UTC-4, Andreas Blixt wrote:
>
> Hello, I have a standard GAE project on Python 2.7 using Flask for
> handling web requests. The project has threadsafe: yes configured.
>
> I'm seeing an issue where two requests that are very close in timing
> failing with two separate errors. Since these errors/requests come in pairs
> often, I believe they're related.
>
> One error will say "Deadlock waiting for <Future ...>" with an arbitrary
> stack trace, the other will be the following set_result cannot be called
> twice:
>
> Traceback (most recent call last):
> File
> "/base/data/home/apps/s~appname/2017-07-26-002.402945478053763657/lib/appname/flask_extras.py",
>
> line 91, in wrap
> result = func(*args, **kwargs)
> File
> "/base/data/home/apps/s~appname/2017-07-26-002.402945478053763657/appname/auth.py",
>
> line 242, in wrap
> result = func(session, *args, **kwargs)
> File
> "/base/data/home/apps/s~appname/2017-07-26-002.402945478053763657/appname/apps/api.py",
>
> line 695, in post_content_content_id_votes
> _wait_all(futures)
> File
> "/base/data/home/runtimes/python27/python27_lib/versions/1/google/appengine/ext/ndb/tasklets.py",
>
> line 1087, in synctasklet_wrapper
> return taskletfunc(*args, **kwds).get_result()
> File
> "/base/data/home/runtimes/python27/python27_lib/versions/1/google/appengine/ext/ndb/tasklets.py",
>
> line 383, in get_result
> self.check_success()
> File
> "/base/data/home/runtimes/python27/python27_lib/versions/1/google/appengine/ext/ndb/tasklets.py",
>
> line 378, in check_success
> self.wait()
> File
> "/base/data/home/runtimes/python27/python27_lib/versions/1/google/appengine/ext/ndb/tasklets.py",
>
> line 362, in wait
> if not ev.run1():
> File
> "/base/data/home/runtimes/python27/python27_lib/versions/1/google/appengine/ext/ndb/eventloop.py",
>
> line 268, in run1
> delay = self.run0()
> File
> "/base/data/home/runtimes/python27/python27_lib/versions/1/google/appengine/ext/ndb/eventloop.py",
>
> line 230, in run0
> callback(*args, **kwds)
> File
> "/base/data/home/runtimes/python27/python27_lib/versions/1/google/appengine/ext/ndb/tasklets.py",
>
> line 533, in _on_future_completion
> self._help_tasklet_along(ns, ds_conn, gen, val)
> File
> "/base/data/home/runtimes/python27/python27_lib/versions/1/google/appengine/ext/ndb/tasklets.py",
>
> line 444, in _help_tasklet_along
> self.set_result(result)
> File
> "/base/data/home/runtimes/python27/python27_lib/versions/1/google/appengine/ext/ndb/tasklets.py",
>
> line 322, in set_result
> raise RuntimeError('Result cannot be set twice.')
> RuntimeError: Result cannot be set twice.
>
> Is there any obvious reasons why this would happen? Could it be the
> treadsafe configuration?
>
> As far as I've been able to confirm, I don't call get_result() or perform
> any synchronous ndb calls in any of the crashing functions, and I wait for
> all Futures to complete before returning from the function (that said,
> would ndb.toplevel(...) have any effect in this case?)
>
> Appreciate any help!
>
>
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