Parametrize rw test with variable frame sizes

Demonstrates fixed size frame-oriented reads by the child where the
parent only transmits a "read" stream msg on "frame fill events" such
that the child incrementally reads the shm list data (much like in
a real-time-buffered streaming system).

tests/test_shm.py

@@ -24,7 +24,10 @@ async def child_attach_shml_alot(
 
     # now try to attach a boatload of times in a loop..
     for _ in range(1000):
-        shml = attach_shm_list(key=shm_key)
+        shml = attach_shm_list(
+            key=shm_key,
+            readonly=False,
+        )
         assert shml.shm.name == shm_key
         await trio.sleep(0.001)
 
@@ -46,8 +49,8 @@ def test_child_attaches_alot():
 
             async with (
                 portal.open_context(
-                    child_attach_shml_alot,  # taken from pytest parameterization
-                    shm_key=key,
+                    child_attach_shml_alot,
+                    shm_key=shml.key,
                 ) as (ctx, start_val),
             ):
                 assert start_val == key
@@ -63,50 +66,70 @@ async def child_read_shm_list(
     ctx: tractor.Context,
     shm_key: str,
     use_str: bool,
+    frame_size: int,
 ) -> None:
 
+    # attach in child
     shml = attach_shm_list(key=shm_key)
     await ctx.started(shml.key)
 
     async with ctx.open_stream() as stream:
         async for i in stream:
-            print(f'reading shm list index: {i}')
+            print(f'(child): reading shm list index: {i}')
 
             if use_str:
                 expect = str(float(i))
             else:
                 expect = float(i)
 
-            assert expect == shml[i]
+            if frame_size == 1:
+                val = shml[i]
+                assert expect == val
+                print(f'(child): reading value: {val}')
+            else:
+                frame = shml[i - frame_size:i]
+                print(f'(child): reading frame: {frame}')
 
 
 @pytest.mark.parametrize(
     'use_str', [False, True],
 )
+@pytest.mark.parametrize(
+    'frame_size',
+    [1, 2**6, 2**10],
+    ids=lambda i: f'frame_size={i}',
+)
 def test_parent_writer_child_reader(
     use_str: bool,
+    frame_size: int,
 ):
 
     async def main():
-        async with tractor.open_nursery() as an:
-
-            # allocate writeable list in parent
-            key = 'shm_list'
-            shml = open_shm_list(
-                key=key,
-                readonly=False,
-            )
+        async with tractor.open_nursery(
+            debug_mode=True,
+        ) as an:
 
             portal = await an.start_actor(
                 'shm_reader',
                 enable_modules=[__name__],
+                debug_mode=True,
+            )
+
+            # allocate writeable list in parent
+            key = 'shm_list'
+            seq_size = int(2 * 2 ** 10)
+            shml = open_shm_list(
+                key=key,
+                size=seq_size,
+                readonly=False,
             )
 
             async with (
                 portal.open_context(
-                    child_read_shm_list,  # taken from pytest parameterization
+                    child_read_shm_list,
                     shm_key=key,
                     use_str=use_str,
+                    frame_size=frame_size,
                 ) as (ctx, sent),
 
                 ctx.open_stream() as stream,
@@ -114,14 +137,23 @@ def test_parent_writer_child_reader(
 
                 assert sent == key
 
-                for i in range(2 ** 10):
+                for i in range(seq_size):
 
                     val = float(i)
                     if use_str:
                         val = str(val)
 
-                    print(f'writing {val}')
+                    print(f'(parent): writing {val}')
                     shml[i] = val
+
+                    # only on frame fills do we
+                    # signal to the child that a frame's
+                    # worth is ready.
+                    if (i % frame_size) == 0:
+                        print(f'(parent): signalling frame full on {val}')
+                        await stream.send(i)
+                else:
+                    print(f'(parent): signalling final frame on {val}')
                     await stream.send(i)
 
             await portal.cancel_actor()