.brokers._daemon: add notes around needed brokerd respawn tech

piker/brokers/_daemon.py

@@ -19,9 +19,12 @@ Broker-daemon-actor "endpoint-hooks": the service task entry points for
 ``brokerd``.
 
 '''
+from __future__ import annotations
 from contextlib import (
     asynccontextmanager as acm,
 )
+from typing import TYPE_CHECKING
+import exceptiongroup as eg
 
 import tractor
 import trio
@@ -29,6 +32,9 @@ import trio
 from . import _util
 from . import get_brokermod
 
+if TYPE_CHECKING:
+    from ..data import _FeedsBus
+
 # `brokerd` enabled modules
 # TODO: move this def to the `.data` subpkg..
 # NOTE: keeping this list as small as possible is part of our caps-sec
@@ -69,17 +75,25 @@ async def _setup_persistent_brokerd(
     # set global for this actor to this new process-wide instance B)
     _util.log = log
 
-    from piker.data.feed import (
-        _bus,
-        get_feed_bus,
-    )
-    global _bus
-    assert not _bus
+    from piker.data import feed
+    assert not feed._bus
 
+    # allocate a nursery to the bus for spawning background
+    # tasks to service client IPC requests, normally
+    # `tractor.Context` connections to explicitly required
+    # `brokerd` endpoints such as:
+    # - `stream_quotes()`,
+    # - `manage_history()`,
+    # - `allocate_persistent_feed()`,
+    # - `open_symbol_search()`
+    # NOTE: see ep invocation details inside `.data.feed`.
+    try:
         async with trio.open_nursery() as service_nursery:
-        # assign a nursery to the feeds bus for spawning
-        # background tasks from clients
-        get_feed_bus(brokername, service_nursery)
+            bus: _FeedsBus = feed.get_feed_bus(
+                brokername,
+                service_nursery,
+            )
+            assert bus is feed._bus
 
             # unblock caller
             await ctx.started()
@@ -88,6 +102,14 @@ async def _setup_persistent_brokerd(
             # parent actor decides to tear it down
             await trio.sleep_forever()
 
+    except eg.ExceptionGroup:
+        # TODO: likely some underlying `brokerd` IPC connection
+        # broke so here we handle a respawn and re-connect attempt!
+        # This likely should pair with development of the OCO task
+        # nusery in dev over @ `tractor` B)
+        # https://github.com/goodboy/tractor/pull/363
+        raise
+
 
 async def spawn_brokerd(
 

piker/data/feed.py

@@ -190,7 +190,7 @@ _bus: _FeedsBus = None
 
 def get_feed_bus(
     brokername: str,
-    nursery: Optional[trio.Nursery] = None,
+    nursery: trio.Nursery | None = None,
 
 ) -> _FeedsBus:
     '''