Merge pull request #264 from goodboy/runinactor_none_result

Fix `Portal.run_in_actor()` returns `None` result

newsfragments/264.bug.rst

@@ -0,0 +1,8 @@
+Fix ``Portal.run_in_actor()`` returns ``None`` result.
+
+``None`` was being used as the cached result flag and obviously breaks
+on a ``None`` returned from the remote target task. This would cause an
+infinite hang if user code ever called ``Portal.result()`` *before* the
+nursery exit. The simple fix is to use the *return message* as the
+initial "no-result-received-yet" flag value and, once received, the
+return value is read from the message to avoid the cache logic error.

tests/test_spawning.py

@@ -1,7 +1,7 @@
 """
 Spawning basics
 """
-from typing import Dict, Tuple
+from typing import Dict, Tuple, Optional
 
 import pytest
 import trio
@@ -93,24 +93,38 @@ async def test_movie_theatre_convo(start_method):
         await portal.cancel_actor()
 
 
-async def cellar_door():
-    return "Dang that's beautiful"
+async def cellar_door(return_value: Optional[str]):
+    return return_value
 
 
+@pytest.mark.parametrize(
+    'return_value', ["Dang that's beautiful", None],
+    ids=['return_str', 'return_None'],
+)
 @tractor_test
-async def test_most_beautiful_word(start_method):
-    """The main ``tractor`` routine.
-    """
-    async with tractor.open_nursery() as n:
+async def test_most_beautiful_word(
+    start_method,
+    return_value
+):
+    '''
+    The main ``tractor`` routine.
 
-        portal = await n.run_in_actor(
-            cellar_door,
-            name='some_linguist',
-        )
+    '''
+    with trio.fail_after(1):
+        async with tractor.open_nursery() as n:
+
+            portal = await n.run_in_actor(
+                cellar_door,
+                return_value=return_value,
+                name='some_linguist',
+            )
 
+            print(await portal.result())
     # The ``async with`` will unblock here since the 'some_linguist'
     # actor has completed its main task ``cellar_door``.
 
+    # this should pull the cached final result already captured during
+    # the nursery block exit.
     print(await portal.result())
 
 

tractor/_portal.py

@@ -21,7 +21,7 @@
 from ._exceptions import (
     unpack_error,
     NoResult,
-    RemoteActorError,
+    # RemoteActorError,
     ContextCancelled,
 )
 from ._streaming import Context, ReceiveMsgStream
@@ -54,8 +54,23 @@ def func_deats(func: Callable) -> Tuple[str, str]:
     )
 
 
+def _unwrap_msg(
+
+    msg: dict[str, Any],
+    channel: Channel
+
+) -> Any:
+    try:
+        return msg['return']
+    except KeyError:
+        # internal error should never get here
+        assert msg.get('cid'), "Received internal error at portal?"
+        raise unpack_error(msg, channel)
+
+
 class Portal:
-    """A 'portal' to a(n) (remote) ``Actor``.
+    '''
+    A 'portal' to a(n) (remote) ``Actor``.
 
     A portal is "opened" (and eventually closed) by one side of an
     inter-actor communication context. The side which opens the portal
@@ -71,13 +86,14 @@ class Portal:
     function calling semantics are supported transparently; hence it is
     like having a "portal" between the seperate actor memory spaces.
 
-    """
+    '''
     def __init__(self, channel: Channel) -> None:
         self.channel = channel
         # when this is set to a tuple returned from ``_submit()`` then
         # it is expected that ``result()`` will be awaited at some point
         # during the portal's lifetime
-        self._result: Optional[Any] = None
+        self._result_msg: Optional[dict] = None
+
         # set when _submit_for_result is called
         self._expect_result: Optional[
             Tuple[str, Any, str, Dict[str, Any]]
@@ -128,16 +144,12 @@ async def _return_once(
         recv_chan: trio.abc.ReceiveChannel,
         resptype: str,
         first_msg: dict
-    ) -> Any:
-        assert resptype == 'asyncfunc'  # single response
 
+    ) -> dict[str, Any]:
+
+        assert resptype == 'asyncfunc'  # single response
         msg = await recv_chan.receive()
-        try:
-            return msg['return']
-        except KeyError:
-            # internal error should never get here
-            assert msg.get('cid'), "Received internal error at portal?"
-            raise unpack_error(msg, self.channel)
+        return msg
 
     async def result(self) -> Any:
         """Return the result(s) from the remote actor's "main" task.
@@ -158,17 +170,11 @@ async def result(self) -> Any:
 
         # expecting a "main" result
         assert self._expect_result
-        if self._result is None:
-            try:
-                self._result = await self._return_once(*self._expect_result)
-            except RemoteActorError as err:
-                self._result = err
 
-        # re-raise error on every call
-        if isinstance(self._result, RemoteActorError):
-            raise self._result
+        if self._result_msg is None:
+            self._result_msg = await self._return_once(*self._expect_result)
 
-        return self._result
+        return _unwrap_msg(self._result_msg, self.channel)
 
     async def _cancel_streams(self):
         # terminate all locally running async generator
@@ -243,22 +249,25 @@ async def run_from_ns(
             instance methods in the remote runtime. Currently this should only
             be used for `tractor` internals.
         """
-        return await self._return_once(
+        msg = await self._return_once(
             *(await self._submit(namespace_path, function_name, kwargs))
         )
+        return _unwrap_msg(msg, self.channel)
 
     async def run(
         self,
         func: str,
         fn_name: Optional[str] = None,
         **kwargs
     ) -> Any:
-        """Submit a remote function to be scheduled and run by actor, in
+        '''
+        Submit a remote function to be scheduled and run by actor, in
         a new task, wrap and return its (stream of) result(s).
 
         This is a blocking call and returns either a value from the
         remote rpc task or a local async generator instance.
-        """
+
+        '''
         if isinstance(func, str):
             warnings.warn(
                 "`Portal.run(namespace: str, funcname: str)` is now"
@@ -284,8 +293,11 @@ async def run(
 
             fn_mod_path, fn_name = func_deats(func)
 
-        return await self._return_once(
-            *(await self._submit(fn_mod_path, fn_name, kwargs))
+        return _unwrap_msg(
+            await self._return_once(
+                *(await self._submit(fn_mod_path, fn_name, kwargs)),
+            ),
+            self.channel,
         )
 
     @asynccontextmanager