Use one nursery per unique manager (signature)

Instead of sticking all `trionics.maybe_open_context()` tasks inside the
actor's (root) service nursery, open a unique one per manager function
instance (id).

Further, accept a callable for the `key` such that a user can have
more flexible control on the caching logic and move the
`maybe_open_nursery()` helper out of the portal mod and into this
trionics "managers" module.

tractor/_portal.py

@@ -35,6 +35,7 @@ import warnings
 import trio
 from async_generator import asynccontextmanager
 
+from .trionics import maybe_open_nursery
 from ._state import current_actor
 from ._ipc import Channel
 from .log import get_logger
@@ -50,25 +51,6 @@ from ._streaming import Context, ReceiveMsgStream
 log = get_logger(__name__)
 
 
-@asynccontextmanager
-async def maybe_open_nursery(
-    nursery: trio.Nursery = None,
-    shield: bool = False,
-) -> AsyncGenerator[trio.Nursery, Any]:
-    '''
-    Create a new nursery if None provided.
-
-    Blocks on exit as expected if no input nursery is provided.
-
-    '''
-    if nursery is not None:
-        yield nursery
-    else:
-        async with trio.open_nursery() as nursery:
-            nursery.cancel_scope.shield = shield
-            yield nursery
-
-
 def _unwrap_msg(
 
     msg: dict[str, Any],

tractor/trionics/__init__.py

@@ -21,6 +21,7 @@ Sugary patterns for trio + tractor designs.
 from ._mngrs import (
     gather_contexts,
     maybe_open_context,
+    maybe_open_nursery,
 )
 from ._broadcast import (
     broadcast_receiver,
@@ -35,4 +36,5 @@ __all__ = [
     'BroadcastReceiver',
     'Lagged',
     'maybe_open_context',
+    'maybe_open_nursery',
 ]

tractor/trionics/_mngrs.py

@@ -19,6 +19,7 @@ Async context manager primitives with hard ``trio``-aware semantics
 
 '''
 from contextlib import asynccontextmanager as acm
+import inspect
 from typing import (
     Any,
     AsyncContextManager,
@@ -35,7 +36,6 @@ import trio
 from trio_typing import TaskStatus
 
 from ..log import get_logger
-from .._state import current_actor
 
 
 log = get_logger(__name__)
@@ -44,6 +44,25 @@ log = get_logger(__name__)
 T = TypeVar("T")
 
 
+@acm
+async def maybe_open_nursery(
+    nursery: trio.Nursery = None,
+    shield: bool = False,
+) -> AsyncGenerator[trio.Nursery, Any]:
+    '''
+    Create a new nursery if None provided.
+
+    Blocks on exit as expected if no input nursery is provided.
+
+    '''
+    if nursery is not None:
+        yield nursery
+    else:
+        async with trio.open_nursery() as nursery:
+            nursery.cancel_scope.shield = shield
+            yield nursery
+
+
 async def _enter_and_wait(
 
     mngr: AsyncContextManager[T],
@@ -128,6 +147,7 @@ class _Cache:
         Hashable,
         tuple[trio.Nursery, trio.Event]
     ] = {}
+    nurseries: dict[int, trio.Nursery] = {}
     no_more_users: Optional[trio.Event] = None
 
     @classmethod
@@ -158,7 +178,7 @@ async def maybe_open_context(
     # XXX: used as cache key after conversion to tuple
     # and all embedded values must also be hashable
     kwargs: dict = {},
-    key: Hashable = None,
+    key: Hashable | Callable[..., Hashable] = None,
 
 ) -> AsyncIterator[tuple[bool, T]]:
     '''
@@ -168,8 +188,14 @@ async def maybe_open_context(
 
     '''
     fid = id(acm_func)
+
+    if inspect.isfunction(key):
+        ctx_key = (fid, key(**kwargs))
+    else:
         ctx_key = (fid, key or tuple(kwargs.items()))
-    value = None
+
+    # yielded output
+    yielded: Any = None
 
     # Lock resource acquisition around task racing  / ``trio``'s
     # scheduler protocol.
@@ -183,40 +209,38 @@ async def maybe_open_context(
         # **critical section** that should prevent other tasks from
         # checking the _Cache until complete otherwise the scheduler
         # may switch and by accident we create more then one resource.
-        value = _Cache.values[ctx_key]
+        yielded = _Cache.values[ctx_key]
 
     except KeyError:
         log.info(f'Allocating new {acm_func} for {ctx_key}')
-
         mngr = acm_func(**kwargs)
-        # TODO: avoid pulling from ``tractor`` internals and
-        # instead offer a "root nursery" in piker actors?
-        service_n = current_actor()._service_n
-
-        # TODO: does this need to be a tractor "root nursery"?
+        service_n: Optional[trio.Nursery] = _Cache.nurseries.get(fid)
+        async with maybe_open_nursery(service_n) as service_n:
+            _Cache.nurseries[fid] = service_n
             resources = _Cache.resources
             assert not resources.get(ctx_key), f'Resource exists? {ctx_key}'
             resources[ctx_key] = (service_n, trio.Event())
 
-        value = await service_n.start(
+            # sync up to the mngr's yielded value
+            yielded = await service_n.start(
                 _Cache.run_ctx,
                 mngr,
                 ctx_key,
             )
             _Cache.users += 1
             lock.release()
-        yield False, value
+            yield False, yielded
 
     else:
         log.info(f'Reusing _Cached resource for {ctx_key}')
         _Cache.users += 1
         lock.release()
-        yield True, value
+        yield True, yielded
 
     finally:
         _Cache.users -= 1
 
-        if value is not None:
+        if yielded is not None:
             # if no more consumers, teardown the client
             if _Cache.users <= 0:
                 log.info(f'De-allocating resource for {ctx_key}')