Avoid blocking the application when computing the calculator report.

cara/apps/calculator/__init__.py

@@ -1,6 +1,8 @@
 # This module is part of CARA. Please see the repository at
 # https://gitlab.cern.ch/cara/cara for details of the license and terms of use.
 
+import asyncio
+import concurrent.futures
 import datetime
 import base64
 import html
@@ -87,7 +89,7 @@ class Missing404Handler(BaseRequestHandler):
 
 
 class ConcentrationModel(BaseRequestHandler):
-    def post(self):
+    async def post(self):
         requested_model_config = {
             name: self.get_argument(name) for name in self.request.arguments
         }
@@ -107,20 +109,27 @@ class ConcentrationModel(BaseRequestHandler):
             return
 
         base_url = self.request.protocol + "://" + self.request.host
-        report_generator = self.settings['report_generator']
-        report = report_generator.build_report(base_url, form)
+        report_generator: ReportGenerator = self.settings['report_generator']
+        report_task = self.settings["worker_pool"].submit(
+            report_generator.build_report, base_url, form,
+        )
+        report: str = await asyncio.wrap_future(report_task)
         self.finish(report)
 
 
 class StaticModel(BaseRequestHandler):
-    def get(self):
+    async def get(self):
         form = model_generator.FormData.from_dict(model_generator.baseline_raw_form_data())
         base_url = self.request.protocol + "://" + self.request.host
-        report_generator = self.settings['report_generator']
-        report = report_generator.build_report(base_url, form)
+        report_generator: ReportGenerator = self.settings['report_generator']
+        report_task = self.settings["worker_pool"].submit(
+            report_generator.build_report, base_url, form,
+        )
+        report: str = await asyncio.wrap_future(report_task)
         self.finish(report)
 
 
+
 class LandingPage(BaseRequestHandler):
     def get(self):
         template = self.settings["template_environment"].get_template(
@@ -226,4 +235,5 @@ def make_app(
         # COOKIE_SECRET being undefined will result in no login information being
         # presented to the user.
         cookie_secret=os.environ.get('COOKIE_SECRET', '<undefined>'),
+        worker_pool=concurrent.futures.ProcessPoolExecutor(),
     )

cara/tests/apps/calculator/test_webapp.py

@@ -48,7 +48,23 @@ class TestBasicApp(tornado.testing.AsyncHTTPTestCase):
 
     @tornado.testing.gen_test(timeout=_TIMEOUT)
     def test_report(self):
-        response = yield self.http_client.fetch(self.get_url('/calculator/baseline-model/result'))
+        requests = [
+            self.http_client.fetch(self.get_url('/calculator/baseline-model/result')),
+            # At the same time, request a non-report page (to check whether the report is blocking).
+            self.http_client.fetch(self.get_url('/calculator/')),
+        ]
+        response = yield requests[0]
+        other_response = yield requests[1]
+
+        def end_time(resp):
+            return resp.start_time + resp.request_time
+
+        # The start time is before the other request,
+        # but the end time is after the other request (because it takes longer
+        # to process a report than a simple page).
+        assert response.start_time < other_response.start_time
+        assert end_time(response) > end_time(other_response)
+
         self.assertEqual(response.code, 200)
         assert 'CERN HSE' not in response.body.decode()
         assert 'expected number of new cases is' in response.body.decode()
@@ -66,6 +82,7 @@ class TestCernApp(tornado.testing.AsyncHTTPTestCase):
         assert 'CERN HSE' in response.body.decode()
         assert 'expected number of new cases is' in response.body.decode()
 
+
 class TestOpenApp(tornado.testing.AsyncHTTPTestCase):
     def get_app(self):
         return cara.apps.calculator.make_app(calculator_prefix="/mycalc")