Android Room Database: Threadsafe usage of database properties

Question

In order to support synchronization of time using NTP for time sensitive data, I've added a Volatile property to our RoomDatabase from where all update operations can request a "timestamp". But I was wondering if this is threadsafe in regards to using Room with suspending functions and transactions? Also not quite sure it actually has to be marked as Volatile as every access should produce a new java.time.Clock.

Example:

abstract class AppDatabase : RoomDatabase() {

    abstract val chatRepository: ChatRepository
    abstract val taskRepository: TaskRepository
    abstract val userSampleRepository: UserRepository

    companion object {
        private const val DB_NAME = "example_database"

        @Volatile
        internal var clock: Clock = Clock.systemDefaultZone()
            private set

        ...
        @JvmStatic
        fun withClock(clock: Clock) {
            synchronized(this) {
                this.clock = clock
            }
        }
    }
}

When used:

abstract class TaskRepository
...
    private suspend fun updateAll(tasks: List<TaskEntity>) = updateAllInternal(
        tasks.map {
            TaskEntity.Builder()
                .copyOf(it)
                .withUpdatedAt(OffsetDateTime.now(AppDatabase.clock))
                .create()
        }
    )
...
}

Related passing tests:

@Test
fun whenRequestingDefaultClock_shouldCreateUpdatedTimestamp() {
    val firstTimestamp = Instant.now(AppDatabase.clock)
    sleep(1) // Adding 1ms delay to ensure Clock is not fixed and returns a different timestamp
    val secondTimestamp = Instant.now(AppDatabase.clock)

    assertThat(firstTimestamp).isLessThan(secondTimestamp)
}

@Test
fun whenSwitchingToFixedClock_shouldUseSameTimestamp() {
    val instant = Instant.now()
    val clock = Clock.fixed(instant, Clock.systemDefaultZone().zone)
    AppDatabase.withClock(clock)
    val firstTimestamp = Instant.now(AppDatabase.clock)
    sleep(1) // Adding 1ms delay to ensure Clock is fixed and returns a fixed timestamp
    val secondTimestamp = Instant.now(AppDatabase.clock)

    assertThat(firstTimestamp).isEqualTo(secondTimestamp)
}

question from:https://stackoverflow.com/questions/65625747/android-room-database-threadsafe-usage-of-database-properties

Answer 1

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