Merge branch 'L2SS-666-fix-clear-poll-cache' into 'master'

L2SS-666: Fix clear poll cache

Closes L2SS-666

See merge request !270

tangostationcontrol/tangostationcontrol/devices/lofar_device.py

@@ -13,7 +13,7 @@
 
 # PyTango imports
 from tango.server import attribute, command, Device, DeviceMeta
-from tango import AttrWriteType, DevState, DebugIt, Attribute, DeviceProxy, AttrDataFormat
+from tango import AttrWriteType, DevState, DebugIt, Attribute, DeviceProxy, AttrDataFormat, DevSource
 import time
 import math
 import numpy
@@ -83,26 +83,6 @@ class lofar_device(Device, metaclass=DeviceMeta):
 
         return self.get_state() in [DevState.STANDBY, DevState.ON, DevState.ALARM]
 
-    def clear_poll_cache(self):
-        """ Remove all attributes from the poll cache, to remove stale entries
-            once we know the values can be read. """
-
-        # we use proxy.attribute_query_list(), as proxy.get_attribute_list() will throw if we
-        # call it too soon when starting everything (database, device) from scratch.
-        attr_names = [config.name for config in self.proxy.attribute_list_query()]
-
-        for attr_name in attr_names:
-            if self.proxy.is_attribute_polled(attr_name):
-                # save poll period
-                poll_period = self.proxy.get_attribute_poll_period(attr_name)
-
-                try:
-                    # stop polling to remove cache entry
-                    self.proxy.stop_poll_attribute(attr_name)
-                finally:
-                    # start polling again
-                    self.proxy.poll_attribute(attr_name, poll_period)
-
     @log_exceptions()
     def init_device(self):
         """ Instantiates the device in the OFF state. """
@@ -123,6 +103,7 @@ class lofar_device(Device, metaclass=DeviceMeta):
         # we cannot write directly to our attribute, as that would not
         # trigger a write_{name} call. See https://www.tango-controls.org/community/forum/c/development/c/accessing-own-deviceproxy-class/?page=1#post-2021
         self.proxy = DeviceProxy(self.get_name())
+        self.proxy.set_source(DevSource.DEV)
 
     @log_exceptions()
     def delete_device(self):
@@ -163,8 +144,14 @@ class lofar_device(Device, metaclass=DeviceMeta):
 
         self.configure_for_initialise()
 
-        # any values read so far are stale. clear the polling cache.
-        self.clear_poll_cache()
+        # WARNING: any values read so far are stale.
+        # Proxies either need to wait for the next poll round, or
+        # use proxy.set_source(DevSource.DEV) to avoid the cache
+        # alltogether.
+        #
+        # Actually clearing the polling cache runs into performance
+        # problems if a lot of attributes are polled, and into race
+        # conditions with the polling thread itself.
 
         self.set_state(DevState.STANDBY)
         self.set_status("Device is in the STANDBY state.")