music-kraken-core/src/music_kraken/objects/cache.py
2023-03-21 12:46:32 +01:00

111 lines
4.0 KiB
Python

from collections import defaultdict
from typing import Dict, List, Optional
import weakref
from .parents import DatabaseObject
"""
This is a cache for the objects, that et pulled out of the database.
This is necessary, to not have duplicate objects with the same id.
Using a cache that maps the ojects to their id has multiple benefits:
- if you modify the object at any point, all objects with the same id get modified *(copy by reference)*
- less ram usage
- to further decrease ram usage I only store weak refs and not a strong reference, for the gc to still work
"""
class ObjectCache:
"""
ObjectCache is a cache for the objects retrieved from a database.
It maps each object to its id and uses weak references to manage its memory usage.
Using a cache for these objects provides several benefits:
- Modifying an object updates all objects with the same id (due to copy by reference)
- Reduced memory usage
:attr object_to_id: Dictionary that maps DatabaseObjects to their id.
:attr weakref_map: Dictionary that uses weak references to DatabaseObjects as keys and their id as values.
:method exists: Check if a DatabaseObject already exists in the cache.
:method append: Add a DatabaseObject to the cache if it does not already exist.
:method extent: Add a list of DatabaseObjects to the cache.
:method remove: Remove a DatabaseObject from the cache by its id.
:method get: Retrieve a DatabaseObject from the cache by its id. """
object_to_id: Dict[str, DatabaseObject]
weakref_map: Dict[weakref.ref, str]
def __init__(self) -> None:
self.object_to_id = dict()
self.weakref_map = defaultdict()
def exists(self, database_object: DatabaseObject) -> bool:
"""
Check if a DatabaseObject with the same id already exists in the cache.
:param database_object: The DatabaseObject to check for.
:return: True if the DatabaseObject exists, False otherwise.
"""
if database_object.dynamic:
return True
return database_object.id in self.object_to_id
def on_death(self, weakref_: weakref.ref) -> None:
"""
Callback function that gets triggered when the reference count of a DatabaseObject drops to 0.
This function removes the DatabaseObject from the cache.
:param weakref_: The weak reference of the DatabaseObject that has been garbage collected.
"""
data_id = self.weakref_map.pop(weakref_)
self.object_to_id.pop(data_id)
def get_weakref(self, database_object: DatabaseObject) -> weakref.ref:
return weakref.ref(database_object, self.on_death)
def append(self, database_object: DatabaseObject) -> bool:
"""
Add a DatabaseObject to the cache.
:param database_object: The DatabaseObject to add to the cache.
:return: True if the DatabaseObject already exists in the cache, False otherwise.
"""
if self.exists(database_object):
return True
self.weakref_map[weakref.ref(database_object, self.on_death)] = database_object.id
self.object_to_id[database_object.id] = database_object
return False
def extent(self, database_object_list: List[DatabaseObject]):
"""
adjacent to the extent method of list, this appends n Object
"""
for database_object in database_object_list:
self.append(database_object)
def remove(self, _id: str):
"""
Remove a DatabaseObject from the cache.
:param _id: The id of the DatabaseObject to remove from the cache.
"""
data = self.object_to_id.get(_id)
if data:
self.weakref_map.pop(weakref.ref(data))
self.object_to_id.pop(_id)
def __getitem__(self, item) -> Optional[DatabaseObject]:
"""
this returns the data obj
:param item: the id of the music object
:return:
"""
return self.object_to_id.get(item)
def get(self, _id: str) -> Optional[DatabaseObject]:
return self.__getitem__(_id)