Convert `iter_ohlc_periods()` to a `@tractor.context`

piker/data/_sampling.py

@@ -133,18 +133,20 @@ async def increment_ohlc_buffer(
             # a given sample period.
             subs = sampler.subscribers.get(delay_s, ())
 
-            for ctx in subs:
+            for stream in subs:
                 try:
-                    await ctx.send_yield({'index': shm._last.value})
+                    await stream.send({'index': shm._last.value})
                 except (
                     trio.BrokenResourceError,
                     trio.ClosedResourceError
                 ):
-                    log.error(f'{ctx.chan.uid} dropped connection')
-                    subs.remove(ctx)
+                    log.error(
+                        f'{stream._ctx.chan.uid} dropped connection'
+                    )
+                    subs.remove(stream)
 
 
-@tractor.stream
+@tractor.context
 async def iter_ohlc_periods(
     ctx: tractor.Context,
     delay_s: int,
@@ -158,18 +160,20 @@ async def iter_ohlc_periods(
     '''
     # add our subscription
     subs = sampler.subscribers.setdefault(delay_s, [])
-    subs.append(ctx)
+    await ctx.started()
+    async with ctx.open_stream() as stream:
+        subs.append(stream)
 
-    try:
-        # stream and block until cancelled
-        await trio.sleep_forever()
-    finally:
         try:
-            subs.remove(ctx)
-        except ValueError:
-            log.error(
-                f'iOHLC step stream was already dropped for {ctx.chan.uid}?'
-            )
+            # stream and block until cancelled
+            await trio.sleep_forever()
+        finally:
+            try:
+                subs.remove(stream)
+            except ValueError:
+                log.error(
+                    f'iOHLC step stream was already dropped {ctx.chan.uid}?'
+                )
 
 
 async def sample_and_broadcast(