Before we go
What is Distributed Lock?
Syncronizing datas or api calls for multiple servers.
Why Redis for Distributed Lock?
Eastest way in my case. Because of not heavy requirements.
Why implementing all the lock codes?
You can use Redisson for lock easly instead of implementing all to locking code. But I need more customizing and using Lettuce already.
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@Service
class DistributeLockService(
private val commonRedisTemplate: RedisTemplate<String, String>,
) {
private val valueOps = commonRedisTemplate.opsForValue()
companion object {
private const val DefaultLockTimeoutMillis = 30_000L
private val ReleaseScript: RedisScript<String> = RedisScript.of("some lock release script")
}
fun <T> doWait(space: String, lockTimeMillis: Long = DefaultLockTimeoutMillis, block: ()->T): T {
val lockName = getLockName(space)
val lockValue = acquireWait(lockName, lockTimeMillis)
return internalDo(lockName, lockValue, lockTimeMillis, block)
}
private fun <T> internalDo(lockName: String, lockValue: String, lockTimeMillis: Long, block: ()->T): T {
val beginAtNanos = System.nanoTime()
return runCatching { block() }
.onSuccess { release(lockName, lockValue, lockTimeMillis, beginAtNanos) }
.getOrElse {
release(lockName, lockValue, lockTimeMillis, beginAtNanos)
throw it
}
}
private fun acquireWait(lockName: String, lockTimeMillis: Long): String {
val lockValue = "" // something unique string
// Wait up to lockTimeMillis with trying to set lockValue to Redis.
// If success to set lockValue, return it. If not throw some kind of Exception.
return lockValue
}
private fun release(lockName: String, lockValue: String, lockTimeMillis: Long, beginAtNanos: Long) {
val elapsedMillis = TimeUtil.calculateTimeGapMillis(beginAtNanos)
if(elapsedMillis > lockTimeMillis) {
return
}
runCatching { commonRedisTemplate.execute(ReleaseScript, mutableListOf(lockName), lockValue) }
}
}
Conclusion
This code call get command to Redis while trying to get lock. So it could be evoke stress to Redis even you did not intend. With Redis pub-sub, it can be less stress for Redis.
