Establish stream before `fsp_compute` so that backfill updates work again..

piker/fsp/_engine.py

@@ -76,7 +76,6 @@ async def filter_quotes_by_sym(
 
 async def fsp_compute(
 
-    ctx: tractor.Context,
     symbol: Symbol,
     feed: Feed,
     quote_stream: trio.abc.ReceiveChannel,
@@ -86,7 +85,7 @@ async def fsp_compute(
 
     func: Callable,
 
-    attach_stream: bool = False,
+    # attach_stream: bool = False,
     task_status: TaskStatus[None] = trio.TASK_STATUS_IGNORED,
 
 ) -> None:
@@ -193,27 +192,22 @@ async def fsp_compute(
     profiler(f'{func_name} pushed history')
     profiler.finish()
 
-    # TODO: UGH, what is the right way to do something like this?
-    if not ctx._started_called:
-        await ctx.started(index)
-
     # setup a respawn handle
     with trio.CancelScope() as cs:
+
+        # TODO: might be better to just make a "restart" method where
+        # the target task is spawned implicitly and then the event is
+        # set via some higher level api? At that poing we might as well
+        # be writing a one-cancels-one nursery though right?
         tracker = TaskTracker(trio.Event(), cs)
         task_status.started((tracker, index))
+
         profiler(f'{func_name} yield last index')
 
         # import time
         # last = time.time()
 
         try:
-            # rt stream
-            async with ctx.open_stream() as stream:
-
-                # always trigger UI refresh after history update,
-                # see ``piker.ui._fsp.FspAdmin.open_chain()`` and
-                # ``piker.ui._display.trigger_update()``.
-                await stream.send('update')
 
             async for processed in out_stream:
 
@@ -225,8 +219,14 @@ async def fsp_compute(
                 # NOTE: for now we aren't streaming this to the consumer
                 # stream latest array index entry which basically just acts
                 # as trigger msg to tell the consumer to read from shm
-                    if attach_stream:
-                        await stream.send(index)
+                # TODO: further this should likely be implemented much
+                # like our `Feed` api where there is one background
+                # "service" task which computes output and then sends to
+                # N-consumers who subscribe for the real-time output,
+                # which we'll likely want to implement using local-mem
+                # chans for the fan out?
+                # if attach_stream:
+                #     await client_stream.send(index)
 
                 # period = time.time() - last
                 # hz = 1/period if period else float('nan')
@@ -320,7 +320,6 @@ async def cascade(
             fsp_target = partial(
 
                 fsp_compute,
-                ctx=ctx,
                 symbol=symbol,
                 feed=feed,
                 quote_stream=quote_stream,
@@ -329,7 +328,7 @@ async def cascade(
                 src=src,
                 dst=dst,
 
-                # func_name=func_name,
+                # target
                 func=func
             )
 
@@ -341,13 +340,34 @@ async def cascade(
 
             profiler(f'{func_name}: fsp up')
 
-            async def resync(tracker: TaskTracker) -> tuple[TaskTracker, int]:
+            # sync client
+            await ctx.started(index)
+
+            # XXX:  rt stream with client which we MUST
+            # open here (and keep it open) in order to make
+            # incremental "updates" as history prepends take
+            # place.
+            async with ctx.open_stream() as client_stream:
+
+                # TODO: these likely should all become
+                # methods of this ``TaskLifetime`` or wtv
+                # abstraction..
+                async def resync(
+                    tracker: TaskTracker,
+
+                ) -> tuple[TaskTracker, int]:
                     # TODO: adopt an incremental update engine/approach
                     # where possible here eventually!
                     log.warning(f're-syncing fsp {func_name} to source')
                     tracker.cs.cancel()
                     await tracker.complete.wait()
-                return await n.start(fsp_target)
+                    tracker, index = await n.start(fsp_target)
+
+                    # always trigger UI refresh after history update,
+                    # see ``piker.ui._fsp.FspAdmin.open_chain()`` and
+                    # ``piker.ui._display.trigger_update()``.
+                    await client_stream.send('update')
+                    return tracker, index
 
                 def is_synced(
                     src: ShmArray,
@@ -394,7 +414,9 @@ async def cascade(
 
                 # Increment the underlying shared memory buffer on every
                 # "increment" msg received from the underlying data feed.
-            async with feed.index_stream(int(delay_s)) as istream:
+                async with feed.index_stream(
+                    int(delay_s)
+                ) as istream:
 
                     profiler(f'{func_name}: sample stream up')
                     profiler.finish()