improve accuracy of subscription loop timing

asyncua/server/internal_subscription.py

@@ -4,6 +4,7 @@ server side implementation of a subscription object
 
 import logging
 import asyncio
+import time
 
 from typing import Union, Iterable, Dict, List
 from asyncua import ua
@@ -72,9 +73,15 @@ class InternalSubscription:
         """
         Start the publication loop running at the RevisedPublishingInterval.
         """
+        ts = time.time()
+        period = self.data.RevisedPublishingInterval / 1000.0
         try:
+            await self.publish_results()
             while True:
-                await asyncio.sleep(self.data.RevisedPublishingInterval / 1000.0)
+                next_ts = ts + period
+                sleep_time = next_ts - time.time()
+                ts = next_ts
+                await asyncio.sleep(max(sleep_time, 0))
                 await self.publish_results()
         except asyncio.CancelledError:
             self.logger.info('exiting _subscription_loop for %s', self.data.SubscriptionId)

examples/client-example.py

@@ -48,7 +48,7 @@ async def main():
 
         # subscribing to a variable node
         handler = SubHandler()
-        sub = await client.create_subscription(500, handler)
+        sub = await client.create_subscription(10, handler)
         handle = await sub.subscribe_data_change(myvar)
         await asyncio.sleep(0.1)
 
@@ -60,6 +60,8 @@ async def main():
         # calling a method on server
         res = await obj.call_method("2:multiply", 3, "klk")
         _logger.info("method result is: %r", res)
+        while True:
+            await asyncio.sleep(1)
 
 
 if __name__ == "__main__":