Attempt to fix CPU utilisation bug by preventing the heartbeat callback leak in the SSE stream handlers and replacing Timer-based with Event-based threads. Also compiled regexes in advance for DXCC callsign lookups for efficiency, and fixed my misunderstanding of what Queue.empty() does

server/handlers/api/alerts.py

@@ -8,7 +8,7 @@ import tornado
 import tornado_eventsource.handler
 
 from core.prometheus_metrics_handler import api_requests_counter
-from core.utils import serialize_everything
+from core.utils import serialize_everything, empty_queue
 
 SSE_HANDLER_MAX_QUEUE_SIZE = 100
 SSE_HANDLER_QUEUE_CHECK_INTERVAL = 5000
@@ -86,7 +86,11 @@ class APIAlertsStreamHandler(tornado_eventsource.handler.EventSourceHandler):
         try:
             if self.alert_queue in self.sse_alert_queues:
                 self.sse_alert_queues.remove(self.alert_queue)
-            self.alert_queue.empty()
+            empty_queue(self.alert_queue)
+        except:
+            pass
+        try:
+            self.heartbeat.stop()
         except:
             pass
         self.alert_queue = None