Refactor info update background task

We now time the interval between consecutive tasks. This is more precise
than using the constant interval the task is supposed to run at since
there is some drift on each run (~0.004s).

anonstream/__init__.py

@@ -47,6 +47,7 @@ def create_app(config_file):
     app.stream_title = None
     app.stream_uptime = None
     app.stream_viewership = None
+    app.last_info_task = None
 
     # Background tasks' asyncio.sleep tasks, cancelled on shutdown
     app.background_sleep = set()

anonstream/tasks.py

@@ -130,56 +130,58 @@ async def t_broadcast_users_update(iteration):
         broadcast_users_update()
 
 @with_period(CONFIG['TASK_BROADCAST_STREAM_INFO_UPDATE'])
-async def t_broadcast_stream_info_update(iteration):
+@with_timestamp(precise=True)
+async def t_broadcast_stream_info_update(timestamp, iteration):
     if iteration == 0:
         title = await get_stream_title()
-        uptime, viewership = get_stream_uptime_and_viewership()
+        uptime, viewership = get_stream_uptime_and_viewership(rounded=False)
         current_app.stream_title = title
         current_app.stream_uptime = uptime
         current_app.stream_viewership = viewership
     else:
-        payload = {}
+        info = {}
-
         title = await get_stream_title()
-        uptime, viewership = get_stream_uptime_and_viewership()
+        uptime, viewership = get_stream_uptime_and_viewership(rounded=False)
 
         # Check if the stream title has changed
         if current_app.stream_title != title:
             current_app.stream_title = title
-            payload['title'] = title
+            info['title'] = title
 
         # Check if the stream uptime has changed unexpectedly
-        if current_app.stream_uptime is None:
+        last_uptime, current_app.stream_uptime = (
-            expected_uptime = None
+            current_app.stream_uptime, uptime
+        )
+        if last_uptime is None:
+            projected_uptime = None
         else:
-            expected_uptime = (
+            last_info_task_ago = timestamp - current_app.last_info_task
-                current_app.stream_uptime
+            projected_uptime = last_uptime + last_info_task_ago
-                + CONFIG['TASK_BROADCAST_STREAM_INFO_UPDATE']
+        if uptime is None and projected_uptime is None:
-            )
-        current_app.stream_uptime = uptime
-        if uptime is None and expected_uptime is None:
             stats_changed = False
-        elif uptime is None or expected_uptime is None:
+        elif uptime is None or projected_uptime is None:
             stats_changed = True
         else:
-            stats_changed = abs(uptime - expected_uptime) >= 0.5
+            stats_changed = abs(uptime - projected_uptime) >= 0.5
 
         # Check if viewership has changed
         if current_app.stream_viewership != viewership:
             current_app.stream_viewership = viewership
             stats_changed = True
 
+        # Broadcast iff anything has changed
         if stats_changed:
             if uptime is None:
-                payload['stats'] = None
+                info['stats'] = None
             else:
-                payload['stats'] = {
+                info['stats'] = {
-                    'uptime': uptime,
+                    'uptime': round(uptime, 2),
                     'viewership': viewership,
                 }
+        if info:
+            broadcast(USERS, payload={'type': 'info', **info})
 
-        if payload:
+    current_app.last_info_task = timestamp
-            broadcast(USERS, payload={'type': 'info', **payload})
 
 current_app.add_background_task(t_delete_eyes)
 current_app.add_background_task(t_sunset_users)