Add a service checker predicate

piker/_daemon.py

@@ -19,7 +19,7 @@ Structured, daemon tree service management.
 
 """
 from typing import Optional, Union, Callable, Any
-from contextlib import asynccontextmanager
+from contextlib import asynccontextmanager as acm
 from collections import defaultdict
 
 from pydantic import BaseModel
@@ -123,7 +123,7 @@ class Services(BaseModel):
 _services: Optional[Services] = None
 
 
-@asynccontextmanager
+@acm
 async def open_pikerd(
     start_method: str = 'trio',
     loglevel: Optional[str] = None,
@@ -178,7 +178,7 @@ async def open_pikerd(
             yield _services
 
 
-@asynccontextmanager
+@acm
 async def open_piker_runtime(
     name: str,
     enable_modules: list[str] = [],
@@ -219,7 +219,7 @@ async def open_piker_runtime(
         yield tractor.current_actor()
 
 
-@asynccontextmanager
+@acm
 async def maybe_open_runtime(
     loglevel: Optional[str] = None,
     **kwargs,
@@ -242,7 +242,7 @@ async def maybe_open_runtime(
         yield
 
 
-@asynccontextmanager
+@acm
 async def maybe_open_pikerd(
     loglevel: Optional[str] = None,
     **kwargs,
@@ -293,7 +293,34 @@ class Brokerd:
     locks = defaultdict(trio.Lock)
 
 
-@asynccontextmanager
+@acm
+async def find_service(
+    service_name: str,
+
+) -> tractor.Portal:
+
+    log.info(f'Scanning for existing {service_name}')
+    # attach to existing daemon by name if possible
+    async with tractor.find_actor(
+        service_name,
+        arbiter_sockaddr=_registry_addr,
+    ) as portal:
+        yield portal
+
+
+async def check_for_service(
+    service_name: str,
+
+) -> bool:
+    '''
+    Service daemon "liveness" predicate.
+
+    '''
+    async with find_service(service_name) as portal:
+        return portal is not None
+
+
+@acm
 async def maybe_spawn_daemon(
 
     service_name: str,
@@ -323,13 +350,7 @@ async def maybe_spawn_daemon(
     lock = Brokerd.locks[service_name]
     await lock.acquire()
 
-    log.info(f'Scanning for existing {service_name}')
-    # attach to existing daemon by name if possible
-    async with tractor.find_actor(
-        service_name,
-        arbiter_sockaddr=_registry_addr,
-
-    ) as portal:
+    async with find_service(service_name) as portal:
         if portal is not None:
             lock.release()
             yield portal
@@ -415,7 +436,7 @@ async def spawn_brokerd(
     return True
 
 
-@asynccontextmanager
+@acm
 async def maybe_spawn_brokerd(
 
     brokername: str,
@@ -477,7 +498,7 @@ async def spawn_emsd(
     return True
 
 
-@asynccontextmanager
+@acm
 async def maybe_open_emsd(
 
     brokername: str,