Stream and context api tweaks

- drop `shield` input to `MsgStream`
- check for cancel called prior to loading the feeder mem chan
  in `Context.open_stream()`
- warn on a timeout when trying to cancel a remote task from
  `Context.cancel()`
- drop noop endofchannel handler block

tractor/_streaming.py

@@ -51,7 +51,6 @@ class ReceiveMsgStream(trio.abc.ReceiveChannel):
         self,
         ctx: 'Context',  # typing: ignore # noqa
         rx_chan: trio.MemoryReceiveChannel,
-        shield: bool = False,
         _broadcaster: Optional[BroadcastReceiver] = None,
 
     ) -> None:
@@ -295,6 +294,9 @@ class MsgStream(ReceiveMsgStream, trio.abc.Channel):
         '''Send a message over this stream to the far end.
 
         '''
+        # if self._eoc:
+        #     raise trio.ClosedResourceError('This stream is already ded')
+
         await self._ctx.chan.send({'yield': data, 'cid': self._ctx.cid})
 
 
@@ -365,7 +367,7 @@ class Context:
         '''
         side = 'caller' if self._portal else 'callee'
 
-        log.warning(f'Cancelling {side} side of context to {self.chan}')
+        log.warning(f'Cancelling {side} side of context to {self.chan.uid}')
 
         self._cancel_called = True
 
@@ -396,6 +398,10 @@ class Context:
                     log.warning(
                         "May have failed to cancel remote task "
                         f"{cid} for {self._portal.channel.uid}")
+                else:
+                    log.warning(
+                        "Timed out on cancelling remote task "
+                        f"{cid} for {self._portal.channel.uid}")
         else:
             # callee side remote task
 
@@ -439,16 +445,6 @@ class Context:
         # here we create a mem chan that corresponds to the
         # far end caller / callee.
 
-        # NOTE: in one way streaming this only happens on the
-        # caller side inside `Actor.send_cmd()` so if you try
-        # to send a stop from the caller to the callee in the
-        # single-direction-stream case you'll get a lookup error
-        # currently.
-        _, recv_chan = actor.get_memchans(
-            self.chan.uid,
-            self.cid
-        )
-
         # Likewise if the surrounding context has been cancelled we error here
         # since it likely means the surrounding block was exited or
         # killed
@@ -459,6 +455,16 @@ class Context:
                 f'Context around {actor.uid[0]}:{task} was already cancelled!'
             )
 
+        # NOTE: in one way streaming this only happens on the
+        # caller side inside `Actor.send_cmd()` so if you try
+        # to send a stop from the caller to the callee in the
+        # single-direction-stream case you'll get a lookup error
+        # currently.
+        _, recv_chan = actor.get_memchans(
+            self.chan.uid,
+            self.cid
+        )
+
         # XXX: If the underlying channel feeder receive mem chan has
         # been closed then likely client code has already exited
         # a ``.open_stream()`` block prior or there was some other
@@ -482,12 +488,6 @@ class Context:
                 # await trio.lowlevel.checkpoint()
                 yield rchan
 
-            except trio.EndOfChannel:
-                # likely the far end sent us a 'stop' message to
-                # terminate the stream.
-                raise
-
-            else:
                 # XXX: Make the stream "one-shot use".  On exit, signal
                 # ``trio.EndOfChannel``/``StopAsyncIteration`` to the
                 # far end.