Call `MsgStream.aclose()` in `Context.open_stream.__aexit__()`

We weren't doing this originally I *think* just because of the path
dependent nature of the way the code was developed (originally being
mega pedantic about one-way vs. bidirectional streams) but, it doesn't
seem like there's any issue just calling the stream's `.aclose()`; also
have the benefit of just being less code and logic checks B)

tractor/_streaming.py

@@ -97,6 +97,9 @@ class ReceiveMsgStream(trio.abc.ReceiveChannel):
         if self._eoc:
             raise trio.EndOfChannel
 
+        if self._closed:
+            raise trio.ClosedResourceError('This stream was closed')
+
         try:
             msg = await self._rx_chan.receive()
             return msg['yield']
@@ -110,6 +113,9 @@ class ReceiveMsgStream(trio.abc.ReceiveChannel):
             # - 'error'
             # possibly just handle msg['stop'] here!
 
+            if self._closed:
+                raise trio.ClosedResourceError('This stream was closed')
+
             if msg.get('stop') or self._eoc:
                 log.debug(f"{self} was stopped at remote end")
 
@@ -189,7 +195,6 @@ class ReceiveMsgStream(trio.abc.ReceiveChannel):
             return
 
         self._eoc = True
-        self._closed = True
 
         # NOTE: this is super subtle IPC messaging stuff:
         # Relay stop iteration to far end **iff** we're
@@ -206,12 +211,8 @@ class ReceiveMsgStream(trio.abc.ReceiveChannel):
 
         # In the bidirectional case, `Context.open_stream()` will create
         # the `Actor._cids2qs` entry from a call to
-        # `Actor.get_context()` and will send the stop message in
-        # ``__aexit__()`` on teardown so it **does not** need to be
-        # called here.
-        if not self._ctx._portal:
-            # Only for 2 way streams can we can send stop from the
-            # caller side.
+        # `Actor.get_context()` and will call us here to send the stop
+        # msg in ``__aexit__()`` on teardown.
         try:
             # NOTE: if this call is cancelled we expect this end to
             # handle as though the stop was never sent (though if it
@@ -228,7 +229,14 @@ class ReceiveMsgStream(trio.abc.ReceiveChannel):
             # the underlying channel may already have been pulled
             # in which case our stop message is meaningless since
             # it can't traverse the transport.
-                log.debug(f'Channel for {self} was already closed')
+            ctx = self._ctx
+            log.warning(
+                f'Stream was already destroyed?\n'
+                f'actor: {ctx.chan.uid}\n'
+                f'ctx id: {ctx.cid}'
+            )
+
+        self._closed = True
 
         # Do we close the local mem chan ``self._rx_chan`` ??!?
 
@@ -594,30 +602,23 @@ class Context:
         async with MsgStream(
             ctx=self,
             rx_chan=ctx._recv_chan,
-        ) as rchan:
+        ) as stream:
 
             if self._portal:
-                self._portal._streams.add(rchan)
+                self._portal._streams.add(stream)
 
             try:
                 self._stream_opened = True
 
-                # ensure we aren't cancelled before delivering
-                # the stream
+                # XXX: do we need this?
+                # ensure we aren't cancelled before yielding the stream
                 # await trio.lowlevel.checkpoint()
-                yield rchan
+                yield stream
 
-                # XXX: Make the stream "one-shot use".  On exit, signal
+                # NOTE: Make the stream "one-shot use".  On exit, signal
                 # ``trio.EndOfChannel``/``StopAsyncIteration`` to the
                 # far end.
-                try:
-                    await self.send_stop()
-                except trio.BrokenResourceError:
-                    log.warning(
-                        f"Couldn't close: stream already broken?\n"
-                        f'actor: {self.chan.uid}\n'
-                        f'ctx id: {self.cid}'
-                    )
+                await stream.aclose()
 
             finally:
                 if self._portal: