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)
}
