Cache sample step streams per actor

piker/data/feed.py

@@ -355,6 +355,31 @@ async def attach_feed_bus(
             bus._subscribers[symbol].remove(sub)
 
 
+@asynccontextmanager
+async def open_sample_step_stream(
+    portal: tractor.Portal,
+    delay_s: int,
+
+) -> tractor.ReceiveMsgStream:
+    # XXX: this should be singleton on a host,
+    # a lone broker-daemon per provider should be
+    # created for all practical purposes
+    async with maybe_open_ctx(
+        key=delay_s,
+        mngr=portal.open_stream_from(
+            iter_ohlc_periods,
+            delay_s=delay_s,  # must be kwarg
+        ),
+    ) as (cache_hit, istream):
+        if cache_hit:
+            # add a new broadcast subscription for the quote stream
+            # if this feed is likely already in use
+            async with istream.subscribe() as bistream:
+                yield bistream
+        else:
+            yield istream
+
+
 @dataclass
 class Feed:
     """A data feed for client-side interaction with far-process# }}}
@@ -371,7 +396,6 @@ class Feed:
     stream: trio.abc.ReceiveChannel[dict[str, Any]]
 
     _brokerd_portal: tractor._portal.Portal
-    _index_stream: Optional[AsyncIterator[int]] = None
     _trade_stream: Optional[AsyncIterator[dict[str, Any]]] = None
     _max_sample_rate: int = 0
 
@@ -391,20 +415,13 @@ class Feed:
 
     ) -> AsyncIterator[int]:
 
-        if not self._index_stream:
-            # XXX: this should be singleton on a host,
-            # a lone broker-daemon per provider should be
-            # created for all practical purposes
-            async with self._brokerd_portal.open_stream_from(
+        delay_s = delay_s or self._max_sample_rate
 
-                iter_ohlc_periods,
-                delay_s=delay_s or self._max_sample_rate,
-
-            ) as self._index_stream:
-
-                yield self._index_stream
-        else:
-            yield self._index_stream
+        async with open_sample_step_stream(
+            self._brokerd_portal,
+            delay_s,
+        ) as istream:
+            yield istream
 
     async def pause(self) -> None:
         await self.stream.send('pause')