Begin formalizing `Sampler` singleton API

We're moving toward a single actor managing sampler work and distributed
independently of `brokerd` services such that a user can run samplers on
different hosts then real-time data feed infra. Most of the
implementation details include aggregating `.data._sampling` routines
into a new `Sampler` singleton type.

Move the following methods to class methods:
- `.increment_ohlc_buffer()` to allow a single task to increment all
  registered shm buffers.
- `.broadcast()` for IPC relay to all registered clients/shms.

Further add a new `maybe_open_global_sampler()` which allocates
a service nursery and assigns it to the `Sampler.service_nursery`; this
is prep for putting the step incrementer in a singleton service task
higher up the data-layer actor tree.

piker/data/_sampling.py

@@ -33,7 +33,10 @@ import tractor
 import trio
 from trio_typing import TaskStatus
 
-from ..log import get_logger
+from ..log import (
+    get_logger,
+    get_console_log,
+)
 
 if TYPE_CHECKING:
     from ._sharedmem import ShmArray
@@ -45,7 +48,7 @@ log = get_logger(__name__)
 _default_delay_s: float = 1.0
 
 
-class sampler:
+class Sampler:
     '''
     Global sampling engine registry.
 
@@ -53,6 +56,8 @@ class sampler:
     sample period logic.
 
     '''
+    service_nursery: None | trio.Nursery = None
+
     # TODO: we could stick these in a composed type to avoid
     # angering the "i hate module scoped variables crowd" (yawn).
     ohlcv_shms: dict[int, list[ShmArray]] = {}
@@ -67,8 +72,9 @@ class sampler:
     # notified on a step.
     subscribers: dict[int, tractor.Context] = {}
 
-
+    @classmethod
     async def increment_ohlc_buffer(
+        self,
         delay_s: int,
         task_status: TaskStatus[trio.CancelScope] = trio.TASK_STATUS_IGNORED,
     ):
@@ -95,17 +101,17 @@ async def increment_ohlc_buffer(
         # tradable hours?
 
         # adjust delay to compensate for trio processing time
-    ad = min(sampler.ohlcv_shms.keys()) - 0.001
+        ad = min(self.ohlcv_shms.keys()) - 0.001
 
         total_s = 0  # total seconds counted
-    lowest = min(sampler.ohlcv_shms.keys())
+        lowest = min(self.ohlcv_shms.keys())
-    lowest_shm = sampler.ohlcv_shms[lowest][0]
+        lowest_shm = self.ohlcv_shms[lowest][0]
         ad = lowest - 0.001
 
         with trio.CancelScope() as cs:
 
             # register this time period step as active
-        sampler.incrementers[delay_s] = cs
+            self.incrementers[delay_s] = cs
             task_status.started(cs)
 
             while True:
@@ -118,7 +124,7 @@ async def increment_ohlc_buffer(
                 # TODO:
                 # - this in ``numba``
                 # - just lookup shms for this step instead of iterating?
-            for this_delay_s, shms in sampler.ohlcv_shms.items():
+                for this_delay_s, shms in self.ohlcv_shms.items():
 
                     # short-circuit on any not-ready because slower sample
                     # rate consuming shm buffers.
@@ -128,7 +134,8 @@ async def increment_ohlc_buffer(
 
                     # TODO: ``numba`` this!
                     for shm in shms:
-                    # append new entry to buffer thus "incrementing" the bar
+                        # append new entry to buffer thus "incrementing"
+                        # the bar
                         array = shm.array
                         last = array[-1:][shm._write_fields].copy()
 
@@ -145,7 +152,8 @@ async def increment_ohlc_buffer(
 
                         # print(f'epoch {shm.token["shm_name"]}: {next_t}')
 
-                    # this copies non-std fields (eg. vwap) from the last datum
+                        # this copies non-std fields (eg. vwap) from the
+                        # last datum
                         last[[
                             'time',
 
@@ -168,18 +176,20 @@ async def increment_ohlc_buffer(
                             0,  # vlm
                         )
 
-                    # TODO: in theory we could make this faster by copying the
+                        # TODO: in theory we could make this faster by
-                    # "last" readable value into the underlying larger buffer's
+                        # copying the "last" readable value into the
-                    # next value and then incrementing the counter instead of
+                        # underlying larger buffer's next value and then
-                    # using ``.push()``?
+                        # incrementing the counter instead of using
+                        # ``.push()``?
 
                         # write to the buffer
                         shm.push(last)
 
-            await broadcast(delay_s, shm=lowest_shm)
+                await self.broadcast(delay_s, shm=lowest_shm)
-
 
+    @classmethod
     async def broadcast(
+        self,
         delay_s: int,
         shm: ShmArray | None = None,
 
@@ -192,17 +202,17 @@ async def broadcast(
         the buffer's non-empty data.
 
         '''
-    subs = sampler.subscribers.get(delay_s, ())
+        subs = self.subscribers.get(delay_s, ())
         first = last = -1
 
         if shm is None:
-        periods = sampler.ohlcv_shms.keys()
+            periods = self.ohlcv_shms.keys()
             # if this is an update triggered by a history update there
             # might not actually be any sampling bus setup since there's
             # no "live feed" active yet.
             if periods:
                 lowest = min(periods)
-            shm = sampler.ohlcv_shms[lowest][0]
+                shm = self.ohlcv_shms[lowest][0]
                 first = shm._first.value
                 last = shm._last.value
 
@@ -227,6 +237,32 @@ async def broadcast(
                         f'{stream._ctx.chan.uid} sub already removed!?'
                     )
 
+    @classmethod
+    async def broadcast_all(self) -> None:
+        for delay_s in self.subscribers:
+            await self.broadcast(delay_s)
+
+
+@tractor.context
+async def maybe_open_global_sampler(
+    ctx: tractor.Context,
+    brokername: str,
+
+) -> None:
+    get_console_log(tractor.current_actor().loglevel)
+
+    global Sampler
+
+    async with trio.open_nursery() as service_nursery:
+        Sampler.service_nursery = service_nursery
+
+        # unblock caller
+        await ctx.started()
+
+        # we pin this task to keep the feeds manager active until the
+        # parent actor decides to tear it down
+        await trio.sleep_forever()
+
 
 @tractor.context
 async def iter_ohlc_periods(
@@ -241,7 +277,7 @@ async def iter_ohlc_periods(
 
     '''
     # add our subscription
-    subs = sampler.subscribers.setdefault(delay_s, [])
+    subs = Sampler.subscribers.setdefault(delay_s, [])
     await ctx.started()
     async with ctx.open_stream() as stream:
         subs.append(stream)

piker/data/feed.py

@@ -74,9 +74,7 @@ from ._source import (
 )
 from ..ui import _search
 from ._sampling import (
-    sampler,
+    Sampler,
-    broadcast,
-    increment_ohlc_buffer,
     sample_and_broadcast,
     uniform_rate_send,
     _default_delay_s,
@@ -327,8 +325,7 @@ async def start_backfill(
         # TODO: *** THIS IS A BUG ***
         # we need to only broadcast to subscribers for this fqsn..
         # otherwise all fsps get reset on every chart..
-        for delay_s in sampler.subscribers:
+        await Sampler.broadcast_all()
-            await broadcast(delay_s)
 
         # signal that backfilling to tsdb's end datum is complete
         bf_done = trio.Event()
@@ -496,8 +493,7 @@ async def start_backfill(
         # in the block above to avoid entering new ``frames``
         # values while we're pipelining the current ones to
         # memory...
-        for delay_s in sampler.subscribers:
+        await Sampler.broadcast_all()
-            await broadcast(delay_s)
 
         # short-circuit (for now)
         bf_done.set()
@@ -738,8 +734,7 @@ async def tsdb_backfill(
                 #   (usually a chart showing graphics for said fsp)
                 #   which tells the chart to conduct a manual full
                 #   graphics loop cycle.
-                for delay_s in sampler.subscribers:
+                await Sampler.broadcast_all()
-                    await broadcast(delay_s)
 
                 # TODO: write new data to tsdb to be ready to for next read.
 
@@ -1037,7 +1032,7 @@ async def allocate_persistent_feed(
 
     # insert 1s ohlc into the increment buffer set
     # to update and shift every second
-    sampler.ohlcv_shms.setdefault(
+    Sampler.ohlcv_shms.setdefault(
         1,
         []
     ).append(rt_shm)
@@ -1053,13 +1048,13 @@ async def allocate_persistent_feed(
 
     # insert 1m ohlc into the increment buffer set
     # to shift every 60s.
-    sampler.ohlcv_shms.setdefault(60, []).append(hist_shm)
+    Sampler.ohlcv_shms.setdefault(60, []).append(hist_shm)
 
     # create buffer a single incrementer task broker backend
     # (aka `brokerd`) using the lowest sampler period.
-    if sampler.incrementers.get(_default_delay_s) is None:
+    if Sampler.incrementers.get(_default_delay_s) is None:
         await bus.start_task(
-            increment_ohlc_buffer,
+            Sampler.increment_ohlc_buffer,
             _default_delay_s,
         )