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

alertproviders/http_alert_provider.py

@@ -1,7 +1,6 @@
 import logging
 from datetime import datetime
-from threading import Timer, Thread
-from time import sleep
+from threading import Thread, Event
 
 import pytz
 import requests
@@ -18,22 +17,25 @@ class HTTPAlertProvider(AlertProvider):
         super().__init__(provider_config)
         self.url = url
         self.poll_interval = poll_interval
-        self.poll_timer = None
+        self._stop_event = Event()
 
     def start(self):
-        # Fire off a one-shot thread to run poll() for the first time, just to ensure start() returns immediately and
-        # the application can continue starting. The thread itself will then die, and the timer will kick in on its own
-        # thread.
+        # Fire off the polling thread. It will poll immediately on startup, then sleep for poll_interval between
+        # subsequent polls, so start() returns immediately and the application can continue starting.
         logging.info("Set up query of " + self.name + " alert API every " + str(self.poll_interval) + " seconds.")
-        thread = Thread(target=self.poll)
-        thread.daemon = True
-        thread.start()
+        self._thread = Thread(target=self._run, daemon=True)
+        self._thread.start()
 
     def stop(self):
-        if self.poll_timer:
-            self.poll_timer.cancel()
+        self._stop_event.set()
 
-    def poll(self):
+    def _run(self):
+        while True:
+            self._poll()
+            if self._stop_event.wait(timeout=self.poll_interval):
+                break
+
+    def _poll(self):
         try:
             # Request data from API
             logging.debug("Polling " + self.name + " alert API...")
@@ -51,10 +53,8 @@ class HTTPAlertProvider(AlertProvider):
         except Exception as e:
             self.status = "Error"
             logging.exception("Exception in HTTP JSON Alert Provider (" + self.name + ")")
-            sleep(1)
-
-        self.poll_timer = Timer(self.poll_interval, self.poll)
-        self.poll_timer.start()
+            # Brief pause on error before the next poll, but still respond promptly to stop()
+            self._stop_event.wait(timeout=1)
 
     # Convert an HTTP response returned by the API into alert data. The whole response is provided here so the subclass
     # implementations can check for HTTP status codes if necessary, and handle the response as JSON, XML, text, whatever