Added @ensure_initialized decorator to actions in variable.

The `variable` plugin may break in the constructor the first time the
application is started.

That's because it tries to initialize the cache of stored variables, but
the local database hasn't yet been initialized.

That's because plugins are registered _before_ the entities engine is
initialized, as the entities engine assumes that it already has plugins
to scan for entities.

Therefore, the initialization of the `variable` plugin's cache should be
lazy (only done upon the first call to `get`/`set` etc.), in order to
prevent deadlock situations where the plugin waits for the engine to
start, but the engine will be initialized only after the plugin is
ready.

And the lazy initialization logic should also ensure that the entities
engine has been properly started (and emit a `TimeoutError` if that's
not the case), in order to prevent race conditions.
This commit is contained in:
Fabio Manganiello 2023-08-17 02:47:30 +02:00
parent adfedfa2dd
commit bf7d060b81
Signed by untrusted user: blacklight
GPG key ID: D90FBA7F76362774

View file

@ -1,11 +1,45 @@
from typing import Collection, Dict, Iterable, Optional, Union
from functools import wraps
from threading import Event, RLock
from typing import Any, Callable, Collection, Dict, Iterable, Optional, Union
from typing_extensions import override
from platypush.entities import EntityManager
from platypush.entities import EntityManager, get_entities_engine
from platypush.entities.variables import Variable
from platypush.plugins import Plugin, action
# pylint: disable=protected-access
def ensure_initialized(f: Callable[..., Any]):
"""
Ensures that the entities engine has been initialized before
reading/writing the db.
It also performs lazy initialization of the variables in the local cache.
"""
@wraps(f)
def wrapper(*args, **kwargs):
self: VariablePlugin = args[0]
if not self._initialized.is_set():
with self._init_lock:
get_entities_engine(timeout=20)
if not self._initialized.is_set():
self._initialized.set()
with self._db.get_session() as session:
self._db_vars.update(
{ # type: ignore
str(var.name): var.value
for var in session.query(Variable).all()
}
)
return f(*args, **kwargs)
return wrapper
class VariablePlugin(Plugin, EntityManager):
"""
This plugin allows you to manipulate context variables that can be
@ -17,18 +51,15 @@ class VariablePlugin(Plugin, EntityManager):
def __init__(self, **kwargs):
super().__init__(**kwargs)
db = self._db
self._db_vars: Dict[str, Optional[str]] = {}
""" Local cache for db variables. """
with db.get_session() as session:
self._db_vars.update(
{ # type: ignore
str(var.name): var.value for var in session.query(Variable).all()
}
)
self._initialized = Event()
""" Lazy initialization event for the _db_vars map. """
self._init_lock = RLock()
""" Lock for the _db_vars map initialization. """
@action
@ensure_initialized
def get(self, name: Optional[str] = None, default_value=None):
"""
Get the value of a variable by name from the local db.
@ -45,6 +76,7 @@ class VariablePlugin(Plugin, EntityManager):
)
@action
@ensure_initialized
def set(self, **kwargs):
"""
Set a variable or a set of variables on the local db.
@ -57,6 +89,7 @@ class VariablePlugin(Plugin, EntityManager):
return kwargs
@action
@ensure_initialized
def delete(self, name: str):
"""
Delete a variable from the database.
@ -76,6 +109,7 @@ class VariablePlugin(Plugin, EntityManager):
return True
@action
@ensure_initialized
def unset(self, name: str):
"""
Unset a variable by name if it's set on the local db.
@ -89,6 +123,7 @@ class VariablePlugin(Plugin, EntityManager):
return self.set(**{name: None})
@action
@ensure_initialized
def mget(self, name: str):
"""
Get the value of a variable by name from Redis.
@ -100,6 +135,7 @@ class VariablePlugin(Plugin, EntityManager):
return self._redis.mget([name])
@action
@ensure_initialized
def mset(self, **kwargs):
"""
Set a variable or a set of variables on Redis.
@ -112,6 +148,7 @@ class VariablePlugin(Plugin, EntityManager):
return kwargs
@action
@ensure_initialized
def munset(self, name: str):
"""
Unset a Redis variable by name if it's set
@ -122,6 +159,7 @@ class VariablePlugin(Plugin, EntityManager):
return self._redis.delete(name)
@action
@ensure_initialized
def expire(self, name: str, expire: int):
"""
Set a variable expiration on Redis
@ -157,6 +195,7 @@ class VariablePlugin(Plugin, EntityManager):
@override
@action
@ensure_initialized
def status(self, *_, **__):
variables = {
name: value for name, value in self._db_vars.items() if value is not None