Support not registering for sample-index msgs via `sub_for_broadcasts: bool` flag

piker/data/_sampling.py

@@ -162,7 +162,6 @@ class Sampler:
                     if shm_period_s not in broadcasted:
                         sub_pair = self.subscribers[shm_period_s]
                         sub_pair[0] = i_epoch
-                        print(f'skipping `{shm_period_s}s` sample update')
                         broadcasted.add(shm_period_s)
 
                     # TODO: ``numba`` this!
@@ -174,8 +173,8 @@ class Sampler:
                         array = shm.array
                         last = array[-1:][shm._write_fields].copy()
 
-                        # guard against startup backfilling race with
-                        # empty buffers.
+                        # guard against startup backfilling races where
+                        # the buffer has not yet been filled.
                         if not last.size:
                             continue
 
@@ -288,7 +287,9 @@ async def register_with_sampler(
     ctx: tractor.Context,
     period_s: float,
     shms_by_period: dict[float, dict] | None = None,
-    open_index_stream: bool = True,
+
+    open_index_stream: bool = True,  # open a 2way stream for sample step msgs?
+    sub_for_broadcasts: bool = True,  # sampler side to send step updates?
 
 ) -> None:
 
@@ -341,14 +342,15 @@ async def register_with_sampler(
             if open_index_stream:
                 try:
                     async with ctx.open_stream() as stream:
+                        if sub_for_broadcasts:
                             subs.add(stream)
 
                         # except broadcast requests from the subscriber
                         async for msg in stream:
                             if msg == 'broadcast_all':
                                 await Sampler.broadcast_all()
-
                 finally:
+                    if sub_for_broadcasts:
                         subs.remove(stream)
             else:
                 # if no shms are passed in we just wait until cancelled
@@ -404,6 +406,7 @@ async def spawn_samplerd(
                 portal,
                 register_with_sampler,
                 period_s=1,
+                sub_for_broadcasts=False,
             )
             return True
 
@@ -437,9 +440,10 @@ async def maybe_open_samplerd(
 
 @acm
 async def open_sample_stream(
-    period_s: int,
+    period_s: float,
     shms_by_period: dict[float, dict] | None = None,
     open_index_stream: bool = True,
+    sub_for_broadcasts: bool = True,
 
     cache_key: str | None = None,
     allow_new_sampler: bool = True,
@@ -482,6 +486,7 @@ async def open_sample_stream(
                 'period_s': period_s,
                 'shms_by_period': shms_by_period,
                 'open_index_stream': open_index_stream,
+                'sub_for_broadcasts': sub_for_broadcasts,
             },
         ) as (ctx, first)
     ):