Add support for stream cloning

tractor/_portal.py

@@ -71,15 +71,18 @@ class ReceiveStream(trio.abc.ReceiveChannel):
         try:
             msg = await self._rx_chan.receive()
             return msg['yield']
+
         except trio.ClosedResourceError:
             # when the send is closed we assume the stream has
             # terminated and signal this local iterator to stop
             await self.aclose()
             raise StopAsyncIteration
+
         except trio.Cancelled:
             # relay cancels to the remote task
             await self.aclose()
             raise
+
         except KeyError:
             # internal error should never get here
             assert msg.get('cid'), (
@@ -102,14 +105,25 @@ class ReceiveStream(trio.abc.ReceiveChannel):
         """Cancel associated remote actor task and local memory channel
         on close.
         """
-        if self._rx_chan._closed:
+        rx_chan = self._rx_chan
+        stats = rx_chan.statistics()
+
+        if rx_chan._closed:
             log.warning(f"{self} is already closed")
             return
 
+        if stats.open_receive_channels > 1:
+            # if we've been cloned don't kill the stream
+            log.debug("there are still consumers running keeping stream alive")
+            return
+
         if self._shielded:
             log.warning(f"{self} is shielded, portal channel being kept alive")
             return
 
+        # close the local mem chan
+        rx_chan.close()
+
         cid = self._cid
         with trio.move_on_after(0.5) as cs:
             cs.shield = True
@@ -131,11 +145,16 @@ class ReceiveStream(trio.abc.ReceiveChannel):
                     "May have failed to cancel remote task "
                     f"{cid} for {self._portal.channel.uid}")
 
-        with trio.CancelScope(shield=True):
-            await self._rx_chan.aclose()
-
     def clone(self):
-        return self
+        """Clone this receive channel allowing for multi-task
+        consumption from the same channel.
+
+        """
+        return ReceiveStream(
+            self._cid,
+            self._rx_chan.clone(),
+            self._portal,
+        )
 
 
 class Portal: