Save task references (#475)

* Save a tast reference

Important: Save a reference of the created task,
to avoid a task disappearing mid-execution. The
event loop only keeps weak references to tasks.
A task that isn’t referenced elsewhere may get
garbage collected at any time, even before it’s
done. For reliable “fire-and-forget” background
tasks, gather them in a collection

app/src/server.py

@@ -218,6 +218,7 @@ app = Quart(__name__,
             static_folder='web/static')
 app.secret_key = 'JKLdks.dajlKKKdladkflKwolafallsdfl'
 app.jinja_env.globals.update(url_for=url_for)
+app.background_tasks = set()
 server = Server(app, __name__ == "__main__")
 Web(app, server.trans_path, server.rel_urls)
 
@@ -268,9 +269,13 @@ async def startup_app():    # pragma: no cover
 
     for inv_class, port in [(InverterG3, 5005), (InverterG3P, 10000)]:
         logging.info(f'listen on port: {port} for inverters')
-        loop.create_task(asyncio.start_server(lambda r, w, i=inv_class:
-                                              handle_client(r, w, i),
-                                              '0.0.0.0', port))
+        task = loop.create_task(
+            asyncio.start_server(lambda r, w, i=inv_class:
+                                 handle_client(r, w, i),
+                                 '0.0.0.0', port))
+        app.background_tasks.add(task)
+        task.add_done_callback(app.background_tasks.discard)
+
     ProxyState.set_up(True)
 
 
@@ -294,6 +299,7 @@ async def handle_shutdown():   # pragma: no cover
         await inverter.disc(True)
 
     logging.info('Proxy disconnecting done')
+    app.background_tasks.clear()
 
     await Proxy.class_close(loop)