Use tornado's AnyThreadEventLoopPolicy

[fagu]

Since tornado 5.0 (with python 3), event loops by default have to be created explicitly in each new thread. This commit reinstates the old behavior in AWS and CWS.

http://www.tornadoweb.org/en/stable/asyncio.html#tornado.platform.asyncio.AnyThreadEventLoopPolicy

Apparently, the alternative is to create a new event loop inside each new thread, as described here: https://github.com/tornadoweb/tornado/issues/2183

I wasn't sure where to set the AnyThreadEventLoopPolicy, but the top of main() seemed reasonable...

RWS seems to work without this change.

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This change is 

[codecov[bot]]

Codecov Report

Merging #991 into master will decrease coverage by 0.23%. The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #991      +/-   ##
==========================================
- Coverage   65.05%   64.82%   -0.24%     
==========================================
  Files         230      230              
  Lines       17731    17731              
==========================================
- Hits        11535    11494      -41     
- Misses       6196     6237      +41

Flag	Coverage Δ
#functionaltests	48.03% <ø> (-0.16%)	:arrow_down:
#unittests	45.88% <ø> (-0.09%)	:arrow_down:

Impacted Files	Coverage Δ
cms/server/admin/handlers/base.py	68.1% <0%> (-3.66%)	:arrow_down:
cms/io/service.py	69.94% <0%> (-3.47%)	:arrow_down:
cms/db/util.py	60.14% <0%> (-2.9%)	:arrow_down:
cms/service/ScoringService.py	66.19% <0%> (-2.82%)	:arrow_down:
cms/io/PsycoGevent.py	78.04% <0%> (-2.44%)	:arrow_down:
cms/service/Worker.py	80.41% <0%> (-2.07%)	:arrow_down:
cms/service/workerpool.py	64.35% <0%> (-1.49%)	:arrow_down:
cms/io/rpc.py	94.77% <0%> (-1.05%)	:arrow_down:
cms/service/ProxyService.py	59.79% <0%> (-1.04%)	:arrow_down:
cms/io/triggeredservice.py	90% <0%> (-1%)	:arrow_down:
... and 7 more

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[lw]

Your change is breaking the functional tests.

The policy you are using was introduced in Tornado 5.0. The tests pin it to 4.5, as in Ubuntu 18.04.

[fagu]

Yes, sorry! I've added a check for "tornado version >= 5.0" now.

[lw]

Ok, the commit you just pushed should fix that. I'm not understanding however what you're trying to fix. The Tornado doc page you link mentions utils for bridging Tornado with asyncio. Your code also imports asyncio. We're not using asyncio, however, so how can it cause problems?

[fagu]

I was getting errors like this when opening the AWS web page:

Traceback (most recent call last): File "/usr/lib/python3.7/site-packages/gevent/pywsgi.py", line 975, in handle_one_response self.run_application() File "/usr/lib/python3.7/site-packages/gevent/pywsgi.py", line 922, in run_application self.result = self.application(self.environ, self.start_response) File "/usr/lib/python3.7/site-packages/cms-1.4.dev0-py3.7.egg/cms/io/web_service.py", line 120, in call return self.wsgi_app(environ, start_response) File "/usr/lib/python3.7/site-packages/cms-1.4.dev0-py3.7.egg/cms/server/admin/authentication.py", line 128, in call return self.wsgi_app(environ, start_response) File "/usr/lib/python3.7/site-packages/werkzeug/local.py", line 228, in application return ClosingIterator(app(environ, start_response), self.cleanup) File "/usr/lib/python3.7/site-packages/cms-1.4.dev0-py3.7.egg/cms/server/admin/authentication.py", line 158, in wsgi_app return self._app(environ, my_start_response) File "/usr/lib/python3.7/site-packages/werkzeug/wsgi.py", line 826, in call return app(environ, start_response) File "/usr/lib/python3.7/site-packages/cms-1.4.dev0-py3.7.egg/cms/server/file_middleware.py", line 76, in call return self.wsgi_app(environ, start_response) File "/usr/lib/python3.7/site-packages/werkzeug/wsgi.py", line 48, in return update_wrapper(lambda *a: f(*a)(a[-2:]), f) File "/usr/lib/python3.7/site-packages/cms-1.4.dev0-py3.7.egg/cms/server/file_middleware.py", line 86, in wsgi_app original_response = Response.from_app(self.wrapped_app, environ) File "/usr/lib/python3.7/site-packages/werkzeug/wrappers.py", line 939, in from_app return cls(_run_wsgi_app(app, environ, buffered)) File "/usr/lib/python3.7/site-packages/werkzeug/wrappers.py", line 59, in _run_wsgi_app return _run_wsgi_app(*args) File "/usr/lib/python3.7/site-packages/werkzeug/test.py", line 923, in run_wsgi_app app_rv = app(environ, start_response) File "/usr/lib/python3.7/site-packages/werkzeug/wsgi.py", line 766, in call return self.app(environ, start_response) File "/usr/lib/python3.7/site-packages/werkzeug/wsgi.py", line 766, in call return self.app(environ, start_response) File "/usr/lib/python3.7/site-packages/tornado/wsgi.py", line 83, in call return WSGIAdapter(self)(environ, start_response) File "/usr/lib/python3.7/site-packages/tornado/wsgi.py", line 242, in call self.application(request) File "/usr/lib/python3.7/site-packages/tornado/wsgi.py", line 207, in application, request) File "/usr/lib/python3.7/site-packages/tornado/web.py", line 2097, in call return dispatcher.execute() File "/usr/lib/python3.7/site-packages/tornado/web.py", line 2228, in execute **self.path_kwargs) File "/usr/lib/python3.7/site-packages/tornado/gen.py", line 297, in wrapper future = _create_future() File "/usr/lib/python3.7/site-packages/tornado/gen.py", line 187, in _create_future future = Future() File "/usr/lib/python3.7/asyncio/events.py", line 644, in get_event_loop % threading.current_thread().name) RuntimeError: There is no current event loop in thread 'DummyThread-7'. 2018-08-16T15:22:30Z {'REMOTE_ADDR': '::1', 'REMOTE_PORT': '47688', 'HTTP_HOST': 'localhost:8889', (hidden keys: 24)} failed with RuntimeError

::1 - - [2018-08-16 17:22:30] "GET / HTTP/1.1" 500 161 0.012203 Traceback (most recent call last): File "/usr/lib/python3.7/site-packages/gevent/pywsgi.py", line 975, in handle_one_response self.run_application() File "/usr/lib/python3.7/site-packages/gevent/pywsgi.py", line 922, in run_application self.result = self.application(self.environ, self.start_response) File "/usr/lib/python3.7/site-packages/cms-1.4.dev0-py3.7.egg/cms/io/web_service.py", line 120, in call return self.wsgi_app(environ, start_response) File "/usr/lib/python3.7/site-packages/cms-1.4.dev0-py3.7.egg/cms/server/admin/authentication.py", line 128, in call return self.wsgi_app(environ, start_response) File "/usr/lib/python3.7/site-packages/werkzeug/local.py", line 228, in application return ClosingIterator(app(environ, start_response), self.cleanup) File "/usr/lib/python3.7/site-packages/cms-1.4.dev0-py3.7.egg/cms/server/admin/authentication.py", line 158, in wsgi_app return self._app(environ, my_start_response) File "/usr/lib/python3.7/site-packages/werkzeug/wsgi.py", line 826, in call return app(environ, start_response) File "/usr/lib/python3.7/site-packages/cms-1.4.dev0-py3.7.egg/cms/server/file_middleware.py", line 76, in call return self.wsgi_app(environ, start_response) File "/usr/lib/python3.7/site-packages/werkzeug/wsgi.py", line 48, in return update_wrapper(lambda *a: f(*a)(a[-2:]), f) File "/usr/lib/python3.7/site-packages/cms-1.4.dev0-py3.7.egg/cms/server/file_middleware.py", line 86, in wsgi_app original_response = Response.from_app(self.wrapped_app, environ) File "/usr/lib/python3.7/site-packages/werkzeug/wrappers.py", line 939, in from_app return cls(_run_wsgi_app(app, environ, buffered)) File "/usr/lib/python3.7/site-packages/werkzeug/test.py", line 923, in run_wsgi_app app_rv = app(environ, start_response) File "/usr/lib/python3.7/site-packages/werkzeug/wsgi.py", line 766, in call return self.app(environ, start_response) File "/usr/lib/python3.7/site-packages/werkzeug/wsgi.py", line 766, in call return self.app(environ, start_response) File "/usr/lib/python3.7/site-packages/tornado/wsgi.py", line 83, in call return WSGIAdapter(self)(environ, start_response) File "/usr/lib/python3.7/site-packages/tornado/wsgi.py", line 242, in call self.application(request) File "/usr/lib/python3.7/site-packages/tornado/wsgi.py", line 207, in application, request) File "/usr/lib/python3.7/site-packages/tornado/web.py", line 2097, in call return dispatcher.execute() File "/usr/lib/python3.7/site-packages/tornado/web.py", line 2228, in execute **self.path_kwargs) File "/usr/lib/python3.7/site-packages/tornado/gen.py", line 297, in wrapper future = _create_future() File "/usr/lib/python3.7/site-packages/tornado/gen.py", line 187, in _create_future future = Future() File "/usr/lib/python3.7/asyncio/events.py", line 644, in get_event_loop % threading.current_thread().name) RuntimeError: There is no current event loop in thread 'DummyThread-8'. 2018-08-16T15:22:30Z {'REMOTE_ADDR': '::1', 'REMOTE_PORT': '47690', 'HTTP_HOST': 'localhost:8889', (hidden keys: 24)} failed with RuntimeError

::1 - - [2018-08-16 17:22:30] "GET /favicon.ico HTTP/1.1" 500 161 0.001120

[fagu]

In case that helps, here's another reference to the AnyThreadEventLoopPolicy fix: https://github.com/tornadoweb/tornado/blob/branch5.1/tornado/wsgi.py#L186 I'm guessing only tornado is using asyncio, and for some reason needs help setting it up. :)

[lw]

Tornado should have nothing to do with IO loops or asynchronicity. We take care of it, through gevent, and just use Tornado via WSGI for routing and handling. I didn't look deep into it (yet) but it appears that v5 became "asyncio-only", which could mean that asyncio stuff has creeped into places where it shouldn't be. I don't think we should tolerate Tornado's use of asyncio, so the fix for this issue should go another way (in your fix, Tornado would start an asyncio loop, which most likely won't play nicely with gevent, be starved, and lead to who knows what chaos).

While I was looking at the changelog I read that they deprecated WSGI support (as if one could ever have called it "support") and will remove it in v6. Maybe it's time to replace Tornado by something else. Or to replace gevent by asyncio. Let's see what @stefano-maggiolo is less disgusted by.

[stefano-maggiolo]

[stefano-maggiolo]

I suppose removing Tornado is more pressing. There are talks to have gevent and asyncio play nice and include that in gevent... https://github.com/gevent/gevent/issues/982

[cantonios]

I get the same error. Ubuntu 18.10 seems to install tornado 5.0.2