319 Windows Hang on Exit (#320)

* Blank line formatting.

* Try signal handling in waitress.

* Remove unrecognised SIGQUIT.

* Don't try to handle Unix signals on Windows.

* Forceful kill.

* Cater for everybody.

backend/src/jv2backend/app.py

@@ -80,11 +80,26 @@ def load(self):
         options["log-level"] = "INFO"
     GUnicornApplication(jv2app, options).run()
 
+
+global server
 def go_waitress(jv2app: Flask, args):
-    from waitress import serve
+    from waitress.server import create_server
+    import signal
+    global server
+
+    # serve(jv2app, listen=args.bind, channel_timeout=args.timeout)
+
+    # signal handler, to do something before shutdown service
+    def handle_sig(sig, frame):
+        logging.warning(f"Got signal {sig}, now close worker...")
+        # worker.close()
+        server.close()
 
-    serve(jv2app, listen=args.bind, channel_timeout=args.timeout)
+    for sig in (signal.SIGINT, signal.SIGTERM):
+        signal.signal(sig, handle_sig)
 
+    server = create_server(jv2app, listen=args.bind, channel_timeout=args.timeout)
+    server.run()
 
 
 def go():

frontend/backend.cpp

@@ -19,7 +19,10 @@ Backend::Backend(const QCommandLineParser &args) : process_()
     if (args.isSet(CLIArgs::DebugBackend))
         backendArgs << "-d";
     if (args.isSet(CLIArgs::UseWaitress))
+    {
         backendArgs << "-w";
+        waitressBackend_ = true;
+    }
 
     process_.setArguments(backendArgs);
     process_.setProcessChannelMode(QProcess::ForwardedChannels);
@@ -77,7 +80,12 @@ void Backend::stop()
     // Gracefully inform the backend to quit
     createRequest(createRoute("shutdown"));
 
-    process_.terminate();
+    // Send the TERM signal to gunicorn, but send the KILL signal to waitress. Dontcha just love cross-platform development?
+    if (waitressBackend_)
+        process_.kill();
+    else
+        process_.terminate();
+
     process_.waitForFinished();
 }
 

frontend/backend.h

@@ -25,6 +25,8 @@ class Backend : public QObject
     QProcess process_;
     // Network manager
     QNetworkAccessManager manager_;
+    // Whether we are using waitress-serve backend over gunicorn
+    bool waitressBackend_{false};
 
     private:
     // Return the backend bind address