Make db queries asynchronous in zuul-web

Previously we blocked on db queries because we didn't await on them. We
address this by wrapping the db query in an executor which runs on a
threadpool in the asyncio event loop. This allows us to await the the
task and context switch to handle other connections asyncronously.

Change-Id: I8db001c160e1e11cb7f5a579a2f575652fd9c454

zuul/driver/sql/sqlconnection.py

@@ -12,6 +12,7 @@
 # License for the specific language governing permissions and limitations
 # under the License.
 
+import asyncio
 import logging
 
 from aiohttp import web
@@ -167,6 +168,9 @@ class SqlWebHandler(BaseTenantWebHandler):
         super(SqlWebHandler, self).__init__(
             connection=connection, zuul_web=zuul_web, method=method, path=path)
 
+    def setEventLoop(self, event_loop):
+        self.event_loop = event_loop
+
     def query(self, args):
         build = self.connection.zuul_build_table
         buildset = self.connection.zuul_buildset_table
@@ -202,7 +206,14 @@ class SqlWebHandler(BaseTenantWebHandler):
         builds = []
         with self.connection.engine.begin() as conn:
             query = self.query(args)
-            for row in conn.execute(query):
+            query_task = self.event_loop.run_in_executor(
+                None,
+                conn.execute,
+                query
+            )
+            rows = await asyncio.wait_for(query_task, 30)
+
+            for row in rows:
                 build = dict(row)
                 # Convert date to iso format
                 if row.start_time:

zuul/web/__init__.py

@@ -264,10 +264,12 @@ class ZuulWeb(object):
         self.log_streaming_handler = LogStreamingHandler(self.rpc)
         self.gearman_handler = GearmanHandler(self.rpc)
         self._plugin_routes = []  # type: List[zuul.web.handler.BaseWebHandler]
+        self._connection_handlers = []
         connections = connections or []
         for connection in connections:
-            self._plugin_routes.extend(
+            self._connection_handlers.extend(
                 connection.getWebHandlers(self, self.info))
+        self._plugin_routes.extend(self._connection_handlers)
 
     async def _handleWebsocket(self, request):
         return await self.log_streaming_handler.processRequest(
@@ -364,6 +366,9 @@ class ZuulWeb(object):
 
         self.event_loop = loop
         self.log_streaming_handler.setEventLoop(loop)
+        for handler in self._connection_handlers:
+            if hasattr(handler, 'setEventLoop'):
+                handler.setEventLoop(loop)
 
         app = web.Application()
         for method, path, handler in routes: