Add piker root daemon spawning machinery

Refactor maybe_spawn_brokerd to adapt to new process tree structure
and add a ``maybe_open_pikerd``.

piker/_daemon.py

@@ -0,0 +1,85 @@
+"""
+pikerd daemon lifecylcle & rpc
+"""
+from typing import Optional
+from contextlib import asynccontextmanager
+
+import tractor
+
+from .log import get_logger, get_console_log
+from .brokers import get_brokermod
+
+
+log = get_logger(__name__)
+
+_root_nursery: Optional[tractor._trionics.ActorNursery] = None
+root_dname = 'pikerd'
+root_modules = [
+    __name__,
+    'piker._ems'
+]
+
+
+@asynccontextmanager
+async def maybe_open_pikerd(
+    loglevel: Optional[str] = None
+) -> Optional[tractor._portal.Portal]:
+    """If no ``pikerd`` daemon-root-actor can be found,
+    assume that role and return a portal to myself
+
+    """
+    global _root_nursery
+
+    if loglevel:
+        get_console_log(loglevel)
+
+    async with tractor.find_actor(root_dname) as portal:
+
+        if portal is not None:  # pikerd exists
+            yield portal
+
+        else:  # assume role
+            async with tractor.open_root_actor(
+                name=root_dname,
+                loglevel=loglevel,
+                enable_modules=root_modules
+            ):
+                # init root nursery
+                try:
+                    async with tractor.open_nursery() as nursery:
+                        _root_nursery = nursery
+                        yield None
+                finally:
+                    # client code may block indefinitely so cancel when
+                    # teardown is invoked
+                    await nursery.cancel()
+
+
+# brokerd enable modules
+_data_mods = [
+    'piker.brokers.core',
+    'piker.brokers.data',
+    'piker.data',
+    'piker.data._buffer'
+]
+
+async def spawn_brokerd(
+    brokername,
+    loglevel: Optional[str] = None,
+    **tractor_kwargs
+):
+
+    brokermod = get_brokermod(brokername)
+    dname = f'brokerd.{brokername}'
+    log.info(f'Spawning {brokername} broker daemon')
+    tractor_kwargs = getattr(brokermod, '_spawnkwargs', {})
+
+    # TODO: raise exception when _root_nursery == None?
+    global _root_nursery
+    await _root_nursery.start_actor(
+        dname,
+        enable_modules=_data_mods + [brokermod.__name__],
+        loglevel=loglevel,
+        **tractor_kwargs
+    )
+

piker/data/__init__.py

@@ -29,11 +29,11 @@ from typing import (
     Dict, Any, Sequence, AsyncIterator, Optional
 )
 
-import trio
 import tractor
 
 from ..brokers import get_brokermod
 from ..log import get_logger, get_console_log
+from .._daemon import spawn_brokerd, maybe_open_pikerd
 from ._normalize import iterticks
 from ._sharedmem import (
     maybe_open_shm_array,
@@ -48,7 +48,6 @@ from ._buffer import (
     subscribe_ohlc_for_increment
 )
 
-
 __all__ = [
     'iterticks',
     'maybe_open_shm_array',
@@ -75,15 +74,6 @@ def get_ingestormod(name: str) -> ModuleType:
     return module
 
 
-# capable rpc modules
-_data_mods = [
-    'piker.brokers.core',
-    'piker.brokers.data',
-    'piker.data',
-    'piker.data._buffer',
-]
-
-
 @asynccontextmanager
 async def maybe_spawn_brokerd(
     brokername: str,
@@ -95,11 +85,11 @@ async def maybe_spawn_brokerd(
 ) -> 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)
 
-    brokermod = get_brokermod(brokername)
     dname = f'brokerd.{brokername}'
     async with tractor.find_actor(dname) as portal:
 
@@ -107,32 +97,29 @@ async def maybe_spawn_brokerd(
         if portal is not None:
             yield portal
 
-        else:  # no daemon has been spawned yet
+        else:
+            # 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:
 
-            log.info(f"Spawning {brokername} broker daemon")
+                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)
 
-            # retrieve any special config from the broker mod
-            tractor_kwargs = getattr(brokermod, '_spawn_kwargs', {})
-
-            async with tractor.open_nursery(
-                #debug_mode=debug_mode,
-            ) as nursery:
-                try:
-                    # spawn new daemon
-                    portal = await nursery.start_actor(
-                        dname,
-                        enable_modules=_data_mods + [brokermod.__name__],
+                else:
+                    await pikerd_portal.run(
+                        spawn_brokerd,
+                        brokername=brokername,
                         loglevel=loglevel,
                         debug_mode=debug_mode,
-                        **tractor_kwargs
                     )
-                    async with tractor.wait_for_actor(dname) as portal:
-                        yield portal
 
-                finally:
-                    # client code may block indefinitely so cancel when
-                    # teardown is invoked
-                    await nursery.cancel()
+                async with tractor.wait_for_actor(dname) as portal:
+                    yield portal
 
 
 @dataclass