Introduce a singleton decorator

homeassistant/core.py

@@ -83,8 +83,8 @@
 block_async_io.enable()
 fix_threading_exception_logging()
 
-# pylint: disable=invalid-name
 T = TypeVar("T")
+# pylint: disable=invalid-name
 CALLABLE_T = TypeVar("CALLABLE_T", bound=Callable)
 CALLBACK_TYPE = Callable[[], None]
 # pylint: enable=invalid-name

homeassistant/helpers/device_registry.py

@@ -1,15 +1,15 @@
 """Provide a way to connect entities belonging to one device."""
-from asyncio import Event
 from collections import OrderedDict
 import logging
-from typing import Any, Dict, List, Optional, cast
+from typing import Any, Dict, List, Optional
 import uuid
 
 import attr
 
 from homeassistant.core import callback
 from homeassistant.loader import bind_hass
 
+from .singleton import singleton
 from .typing import HomeAssistantType
 
 # mypy: allow-untyped-calls, allow-untyped-defs, no-check-untyped-defs
@@ -356,26 +356,12 @@ def async_clear_area_id(self, area_id: str) -> None:
 
 
 @bind_hass
+@singleton(DATA_REGISTRY)
 async def async_get_registry(hass: HomeAssistantType) -> DeviceRegistry:
-    """Return device registry instance."""
-    reg_or_evt = hass.data.get(DATA_REGISTRY)
-
-    if not reg_or_evt:
-        evt = hass.data[DATA_REGISTRY] = Event()
-
-        reg = DeviceRegistry(hass)
-        await reg.async_load()
-
-        hass.data[DATA_REGISTRY] = reg
-        evt.set()
-        return reg
-
-    if isinstance(reg_or_evt, Event):
-        evt = reg_or_evt
-        await evt.wait()
-        return cast(DeviceRegistry, hass.data.get(DATA_REGISTRY))
-
-    return cast(DeviceRegistry, reg_or_evt)
+    """Create entity registry."""
+    reg = DeviceRegistry(hass)
+    await reg.async_load()
+    return reg
 
 
 @callback

homeassistant/helpers/entity_registry.py

@@ -7,7 +7,6 @@
 registered. Registering a new entity while a timer is in progress resets the
 timer.
 """
-import asyncio
 from collections import OrderedDict
 import logging
 from typing import (
@@ -39,6 +38,7 @@
 from homeassistant.util import slugify
 from homeassistant.util.yaml import load_yaml
 
+from .singleton import singleton
 from .typing import HomeAssistantType
 
 if TYPE_CHECKING:
@@ -492,26 +492,12 @@ def async_clear_config_entry(self, config_entry: str) -> None:
 
 
 @bind_hass
+@singleton(DATA_REGISTRY)
 async def async_get_registry(hass: HomeAssistantType) -> EntityRegistry:
-    """Return entity registry instance."""
-    reg_or_evt = hass.data.get(DATA_REGISTRY)
-
-    if not reg_or_evt:
-        evt = hass.data[DATA_REGISTRY] = asyncio.Event()
-
-        reg = EntityRegistry(hass)
-        await reg.async_load()
-
-        hass.data[DATA_REGISTRY] = reg
-        evt.set()
-        return reg
-
-    if isinstance(reg_or_evt, asyncio.Event):
-        evt = reg_or_evt
-        await evt.wait()
-        return cast(EntityRegistry, hass.data.get(DATA_REGISTRY))
-
-    return cast(EntityRegistry, reg_or_evt)
+    """Create entity registry."""
+    reg = EntityRegistry(hass)
+    await reg.async_load()
+    return reg
 
 
 @callback
@@ -621,4 +607,4 @@ async def async_migrate_entries(
         updates = entry_callback(entry)
 
         if updates is not None:
-            ent_reg.async_update_entity(entry.entity_id, **updates)  # type: ignore
+            ent_reg.async_update_entity(entry.entity_id, **updates)

homeassistant/helpers/singleton.py

@@ -0,0 +1,44 @@
+"""Helper to help coordinating calls."""
+import asyncio
+import functools
+from typing import Awaitable, Callable, TypeVar, cast
+
+from homeassistant.core import HomeAssistant
+
+T = TypeVar("T")
+
+FUNC = Callable[[HomeAssistant], Awaitable[T]]
+
+
+def singleton(data_key: str) -> Callable[[FUNC], FUNC]:
+    """Decorate a function that should be called once per instance.
+
+    Result will be cached and simultaneous calls will be handled.
+    """
+
+    def wrapper(func: FUNC) -> FUNC:
+        """Wrap a function with caching logic."""
+
+        @functools.wraps(func)
+        async def wrapped(hass: HomeAssistant) -> T:
+            obj_or_evt = hass.data.get(data_key)
+
+            if not obj_or_evt:
+                evt = hass.data[data_key] = asyncio.Event()
+
+                result = await func(hass)
+
+                hass.data[data_key] = result
+                evt.set()
+                return cast(T, result)
+
+            if isinstance(obj_or_evt, asyncio.Event):
+                evt = obj_or_evt
+                await evt.wait()
+                return cast(T, hass.data.get(data_key))
+
+            return cast(T, obj_or_evt)
+
+        return wrapped
+
+    return wrapper

pylintrc

@@ -8,7 +8,7 @@ persistent=no
 extension-pkg-whitelist=ciso8601
 
 [BASIC]
-good-names=id,i,j,k,ex,Run,_,fp
+good-names=id,i,j,k,ex,Run,_,fp,T
 
 [MESSAGES CONTROL]
 # Reasons disabled: