Start forming an services api

Add a `Services` nurseries container singleton for spawning sub-daemons
inside the long running `pikerd` tree. Bring in `brokerd` spawning util
funcs to start getting eyes on what can be factored into a service api.

piker/_daemon.py

@@ -1,9 +1,12 @@
 """
 pikerd daemon lifecylcle & rpc
 """
-from typing import Optional
+from typing import Optional, Union
 from contextlib import asynccontextmanager
+from functools import partial
 
+from pydantic import BaseModel
+import trio
 import tractor
 
 from .log import get_logger, get_console_log
@@ -12,7 +15,6 @@ from .brokers import get_brokermod
 
 log = get_logger(__name__)
 
-_root_nursery: Optional[tractor._trionics.ActorNursery] = None
 _root_dname = 'pikerd'
 _root_modules = [
     __name__,
@@ -21,17 +23,39 @@ _root_modules = [
 ]
 
 
+# @dataclass
+class Services(BaseModel):
+    actor_n: tractor._trionics.ActorNursery
+    service_n: trio.Nursery
+
+    class Config:
+        arbitrary_types_allowed = True
+
+
+_services: Optional[Services] = None
+
+
 @asynccontextmanager
 async def open_pikerd(
     loglevel: Optional[str] = None,
     **kwargs,
 ) -> Optional[tractor._portal.Portal]:
+    """Start a root piker daemon who's lifetime extends indefinitely
+    until cancelled.
 
-    global _root_nursery
+    A root actor nursery is created which can be used to create and keep
+    alive underling services (see below).
+
+    """
+    global _services
+    assert _services is None
 
     # XXX: this may open a root actor as well
     async with tractor.open_nursery(
+
+        # passed through to ``open_root_actor``
         name=_root_dname,
+        loglevel=loglevel,
 
         # TODO: eventually we should be able to avoid
         # having the root have more then permissions to
@@ -39,23 +63,28 @@ async def open_pikerd(
         # enable_modules=[__name__],
         enable_modules=_root_modules,
 
-        loglevel=loglevel,
-    ) as nursery:
-        _root_nursery = nursery
-        yield nursery
+    ) as actor_nursery:
+        async with trio.open_nursery() as service_nursery:
+
+            # assign globally for future daemon/task creation
+            _services = Services(
+                actor_n=actor_nursery,
+                service_n=service_nursery
+            )
+
+            yield _services
 
 
 @asynccontextmanager
 async def maybe_open_pikerd(
     loglevel: Optional[str] = None,
     **kwargs,
-) -> Optional[tractor._portal.Portal]:
-    """If no ``pikerd`` daemon-root-actor can be found,
-    assume that role and return a portal to myself
+) -> Union[tractor._portal.Portal, Services]:
+    """If no ``pikerd`` daemon-root-actor can be found start it and
+    yield up (we should probably figure out returning a portal to self
+    though).
 
     """
-    global _root_nursery
-
     if loglevel:
         get_console_log(loglevel)
 
@@ -72,13 +101,10 @@ async def maybe_open_pikerd(
     async with open_pikerd(
         loglevel,
         **kwargs,
-    ):
-        assert _root_nursery
-
+    ) as _:
         # in the case where we're starting up the
         # tractor-piker runtime stack in **this** process
-        # we want to hand off a nursery for starting (as a sub)
-        # whatever actor is requesting pikerd.
+        # we return no portal to self.
         yield None
 
 
@@ -97,6 +123,8 @@ async def spawn_brokerd(
     **tractor_kwargs
 ) -> tractor._portal.Portal:
 
+    from .data import _setup_persistent_feeds
+
     log.info(f'Spawning {brokername} broker daemon')
 
     brokermod = get_brokermod(brokername)
@@ -105,19 +133,82 @@ async def spawn_brokerd(
     extra_tractor_kwargs = getattr(brokermod, '_spawn_kwargs', {})
     tractor_kwargs.update(extra_tractor_kwargs)
 
-    # TODO: raise exception when _root_nursery == None?
-    global _root_nursery
+    global _services
+    assert _services
 
-    await _root_nursery.start_actor(
+    portal = await _services.actor_n.start_actor(
         dname,
         enable_modules=_data_mods + [brokermod.__name__],
         loglevel=loglevel,
         **tractor_kwargs
     )
 
+    # TODO: so i think this is the perfect use case for supporting
+    # a cross-actor async context manager api instead of this
+    # shoort-and-forget task spawned in the root nursery, we'd have an
+    # async exit stack that we'd register the `portal.open_context()`
+    # call with and then have the ability to unwind the call whenevs.
+
+    # non-blocking setup of brokerd service nursery
+    _services.service_n.start_soon(
+        partial(
+            portal.run,
+            _setup_persistent_feeds,
+            brokername=brokername,
+        )
+    )
+
     return dname
 
 
+@asynccontextmanager
+async def maybe_spawn_brokerd(
+    brokername: str,
+    loglevel: Optional[str] = None,
+
+    # XXX: you should pretty much never want debug mode
+    # for data daemons when running in production.
+    debug_mode: bool = True,
+) -> tractor._portal.Portal:
+    """If no ``brokerd.{brokername}`` daemon-actor can be found,
+    spawn one in a local subactor and return a portal to it.
+
+    """
+    if loglevel:
+        get_console_log(loglevel)
+
+    dname = f'brokerd.{brokername}'
+
+    # attach to existing brokerd if possible
+    async with tractor.find_actor(dname) as portal:
+        if portal is not None:
+            yield portal
+            return
+
+    # ask root ``pikerd`` daemon to spawn the daemon we need if
+    # pikerd is not live we now become the root of the
+    # process tree
+    async with maybe_open_pikerd(
+        loglevel=loglevel
+    ) as pikerd_portal:
+
+        if pikerd_portal is None:
+            # we are root so spawn brokerd directly in our tree
+            # the root nursery is accessed through process global state
+            await spawn_brokerd(brokername, loglevel=loglevel)
+
+        else:
+            await pikerd_portal.run(
+                spawn_brokerd,
+                brokername=brokername,
+                loglevel=loglevel,
+                debug_mode=debug_mode,
+            )
+
+        async with tractor.wait_for_actor(dname) as portal:
+            yield portal
+
+
 async def spawn_emsd(
     brokername,
     loglevel: Optional[str] = None,
@@ -126,10 +217,10 @@ async def spawn_emsd(
 
     log.info('Spawning emsd')
 
-    # TODO: raise exception when _root_nursery == None?
-    global _root_nursery
+    # TODO: raise exception when _services == None?
+    global _services
 
-    await _root_nursery.start_actor(
+    await _services.actor_n.start_actor(
         'emsd',
         enable_modules=[
             'piker.clearing._ems',