Set resent_latest=True for BatteryPool.power_status's channels

RELEASE_NOTES.md

@@ -52,7 +52,9 @@ This version ships an experimental version of the **Power Manager**, adds prelim
 
   This means that one or more inverters can be connected to one or more batteries.
 
-- A `PowerManagingActor` implementation
+- A `PowerManagingActor` implementation.
+
+- Allow configuration of the `resend_latest` flag in channels owned by the `ChannelRegistry`.
 
 ## Bug Fixes
 

src/frequenz/sdk/actor/_channel_registry.py

@@ -28,6 +28,29 @@ def __init__(self, *, name: str) -> None:
         self._name = name
         self._channels: dict[str, Broadcast[typing.Any]] = {}
 
+    def set_resend_latest(self, key: str, resend_latest: bool) -> None:
+        """Set the `resend_latest` flag for a given channel.
+
+        This flag controls whether the latest value of the channel should be resent to
+        new receivers, in slow streams.
+
+        `resend_latest` is `False` by default.  It is safe to be set in data/reporting
+        channels, but is not recommended for use in channels that stream control
+        instructions.
+
+        Args:
+            key: The key to identify the channel.
+            resend_latest: Whether to resend the latest value to new receivers, for the
+                given channel.
+        """
+        if key not in self._channels:
+            self._channels[key] = Broadcast(f"{self._name}-{key}")
+        # This attribute is protected in the current version of the channels library,
+        # but that will change in the future.
+        self._channels[  # pylint: disable=protected-access
+            key
+        ]._resend_latest = resend_latest
+
     def new_sender(self, key: str) -> Sender[typing.Any]:
         """Get a sender to a dynamically created channel with the given key.
 

src/frequenz/sdk/timeseries/battery_pool/_battery_pool.py

@@ -441,6 +441,9 @@ def power_status(self) -> ReceiverFetcher[_power_managing.Report]:
         ] = asyncio.create_task(
             self._battery_pool._power_manager_bounds_subscription_sender.send(sub)
         )
+        self._battery_pool._channel_registry.set_resend_latest(
+            sub.get_channel_name(), True
+        )
         return self._battery_pool._channel_registry.new_receiver_fetcher(
             sub.get_channel_name()
         )