feat. multi process

[DHR60]

No description provided.

[gemini-code-assist]

Code Review

This pull request configures several services to run in a separate ":engine" process and updates the Room database and DataStore instances to support multi-process access. The review feedback highlights critical issues in the new multi-process DataStore implementations, including a compilation error due to referencing the internal "PreferencesFileSerializer", missing "@volatile" annotations on the "INSTANCE" variables for double-checked locking, and unsafe synchronization on a framework class instead of a private lock object.

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[gemini-code-assist]

Concurrency & Thread Safety Issues

1. Missing @Volatile: The INSTANCE variable is used in a double-checked locking pattern but is not marked as @Volatile. Without this, writes to INSTANCE might not be immediately visible to other threads, or the compiler/CPU might reorder instructions, leading to another thread reading a partially initialized INSTANCE.
2. Locking on a Framework Class: Locking on MultiProcessDataStoreFactory::class.java is not recommended. It is a framework class, and locking on it can lead to unexpected contention or deadlocks if other parts of the app or libraries also lock on it. Use a private lock object instead.

Suggested change

	private var INSTANCE: DataStore<ConfigItem>? = null
	val Context.configDataStore: DataStore<ConfigItem>
	get() = INSTANCE ?: synchronized(MultiProcessDataStoreFactory::class.java) {
	INSTANCE ?: MultiProcessDataStoreFactory.create(
	serializer = ConfigItemSerializer,
	produceFile = { this.applicationContext.dataStoreFile("config.json") }
	).also { INSTANCE = it }
	}
	@Volatile
	private var INSTANCE: DataStore<ConfigItem>? = null
	private val lock = Any()
	val Context.configDataStore: DataStore<ConfigItem>
	get() = INSTANCE ?: synchronized(lock) {
	INSTANCE ?: MultiProcessDataStoreFactory.create(
	serializer = ConfigItemSerializer,
	produceFile = { this.applicationContext.dataStoreFile("config.json") }
	).also { INSTANCE = it }
	}

[gemini-code-assist]

Compilation & Concurrency Issues

1. Compilation Error (PreferencesFileSerializer is internal): PreferencesFileSerializer is an internal object in the androidx.datastore.preferences.core package. Referencing it directly here will cause a compilation error. To resolve this, you can copy the implementation of PreferencesFileSerializer into your project or implement a custom serializer for Preferences.
2. Missing @Volatile: The INSTANCE variable is used in a double-checked locking pattern but is not marked as @Volatile.
3. Locking on a Framework Class: Locking on MultiProcessDataStoreFactory::class.java is not recommended. Use a private lock object instead.

Suggested change

	private var INSTANCE: DataStore<Preferences>? = null
	val Context.preferencesDataStore: DataStore<Preferences>
	get() = INSTANCE ?: synchronized(MultiProcessDataStoreFactory::class.java) {
	INSTANCE ?: MultiProcessDataStoreFactory.create(
	serializer = PreferencesFileSerializer,
	produceFile = {
	this.applicationContext.dataStoreFile("config.preferences_pb")
	}
	).also { INSTANCE = it }
	}
	@Volatile
	private var INSTANCE: DataStore<Preferences>? = null
	private val lock = Any()
	val Context.preferencesDataStore: DataStore<Preferences>
	get() = INSTANCE ?: synchronized(lock) {
	INSTANCE ?: MultiProcessDataStoreFactory.create(
	serializer = PreferencesFileSerializer,
	produceFile = {
	this.applicationContext.dataStoreFile("config.preferences_pb")
	}
	).also { INSTANCE = it }
	}