fix PeriodicTimer usage

fixes #4066

Author: vladak

docker/periodic_timer.py

@@ -8,23 +8,24 @@
 
 class PeriodicTimer:
     """
-    Helper class to facilitate waiting for periodic events.
-    Requires the start() function to be called first.
+    Helper class to facilitate waiting for (periodic) events.
+    For periodic events, start() function has to be called first.
     """
 
     def __init__(self, interval):
         """
-        :param interval: interval in seconds
+        :param interval: interval in seconds, can be 0
         """
         self._interval = interval
         self._flag = 0
         self._cv = threading.Condition()
 
     def start(self):
         """
-        Start the notification thread.
+        Start the periodic notification thread if the configured interval is positive.
         """
-        threading.Thread(target=self.run, daemon=True).start()
+        if self._interval > 0:
+            threading.Thread(target=self.run, daemon=True).start()
 
     def run(self):
         """
@@ -34,9 +35,10 @@ def run(self):
             time.sleep(self._interval)
             self.notify_all()
 
-    def wait_for_tick(self):
+    def wait_for_event(self):
         """
-        Wait for the next tick of the timer
+        Wait for the wakeup event. This can be either tick of the timer from run(),
+        or notification via notify_all().
         """
         with self._cv:
             last_flag = self._flag

docker/start.py

@@ -81,11 +81,6 @@
 REINDEX_POINT = '/reindex'
 
 
-def trigger_reindex():
-    # Signal the sync/indexer thread.
-    periodic_timer.notify_all()
-
-
 @auth.verify_token
 def verify_token(token):
     if expected_token is None:
@@ -98,9 +93,16 @@ def verify_token(token):
 @app.route(REINDEX_POINT)
 @auth.login_required
 def index():
-    periodic_timer.notify_all()
+    global periodic_timer
+
+    if periodic_timer:
+        logger = logging.getLogger(__name__)
+        logger.debug("Triggering reindex based on API call")
 
-    return "Reindex triggered"
+        periodic_timer.notify_all()
+        return "Reindex triggered\n"
+
+    return "Reindex not triggered - the timer is not initialized yet\n"
 
 
 def rest_function(logger, rest_port):
@@ -297,7 +299,8 @@ def indexer_no_projects(logger, uri, config_path, extra_indexer_options):
         indexer.execute()
 
         logger.info("Waiting for reindex to be triggered")
-        periodic_timer.wait_for_tick()
+        global periodic_timer
+        periodic_timer.wait_for_event()
 
 
 def project_syncer(logger, loglevel, uri, config_path, numworkers, env):
@@ -346,7 +349,8 @@ def project_syncer(logger, loglevel, uri, config_path, numworkers, env):
             save_config(logger, uri, config_path)
 
         logger.info("Waiting for reindex to be triggered")
-        periodic_timer.wait_for_tick()
+        global periodic_timer
+        periodic_timer.wait_for_event()
 
 
 def create_bare_config(logger, use_projects, extra_indexer_options=None):
@@ -553,6 +557,12 @@ def main():
                        extra_indexer_options)
 
     if sync_enabled:
+        period_seconds = sync_period_mins * 60
+        logger.debug(f"Creating and starting periodic timer (period {period_seconds} seconds)")
+        global periodic_timer
+        periodic_timer = PeriodicTimer(period_seconds)
+        periodic_timer.start()
+
         logger.debug("Starting sync thread")
         sync_thread = threading.Thread(target=worker_function,
                                        name="Sync thread",
@@ -561,11 +571,6 @@ def main():
 
         start_rest_thread(logger)
 
-        if sync_period_mins > 0:
-            global periodic_timer
-            periodic_timer = PeriodicTimer(sync_period_mins * 60)
-            periodic_timer.start()
-
     # Start Tomcat last. It will be the foreground process.
     logger.info("Starting Tomcat")
     global tomcat_popen