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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