Coroutine Context 대한 이해 (feat. Redisson)

By Jimmyberg
kotlin coroutine coroutinecontext redisson

Kotlin 코루틴 Trouble-Shooting (with Redisson 분산락)

Situation

  • Redisson 분산락을 사용하는 lock 함수에서, block() 람다 함수 실행 후에 락이 정상적으로 해제(unlock)되지 않는 현상 발생
-- 1. 정상적으로 `unlock` 되는 경우
2025-05-13 13:04:00.052.DefaultDispatcher-worker-1 @coroutine#1> INFO  T[] U[] M[] - Redisson 'ktc:202505131304:expire-traffic-token-schedule-lock' locked.
2025-05-13 13:04:00.122.DefaultDispatcher-worker-1 @coroutine#1> INFO  T[] U[] M[] - Expired Traffic Token count : 0
2025-05-13 13:04:00.131.DefaultDispatcher-worker-1 @coroutine#1> INFO  T[] U[] M[] - Redisson 'ktc:202505131304:expire-traffic-token-schedule-lock' unlocked.
-- 2. 비정상적으로 `unlock` 되는 경우
2025-05-13 13:05:00.008.DefaultDispatcher-worker-1 @coroutine#2> INFO  T[] U[] M[] - Redisson 'ktc:202505131305:expire-traffic-token-schedule-lock' locked.
2025-05-13 13:05:00.022.DefaultDispatcher-worker-4 @coroutine#2> INFO  T[] U[] M[] - Expired Traffic Token count : 0
-- 3. 비정상적으로 `unlock` 되는 경우
2025-05-13 13:06:00.012.DefaultDispatcher-worker-4 @coroutine#3> INFO  T[] U[] M[] - Redisson 'ktc:202505131306:expire-traffic-token-schedule-lock' locked.
2025-05-13 13:06:00.025.DefaultDispatcher-worker-1 @coroutine#3> INFO  T[] U[] M[] - Expired Traffic Token count : 0
-- 4. 정상적으로 `unlock` 되는 경우
2025-05-13 13:07:00.005.DefaultDispatcher-worker-4 @coroutine#4> INFO  T[] U[] M[] - Redisson 'ktc:202505131307:expire-traffic-token-schedule-lock' locked.
2025-05-13 13:07:00.018.DefaultDispatcher-worker-4 @coroutine#4> INFO  T[] U[] M[] - Expired Traffic Token count : 0
2025-05-13 13:07:00.020.DefaultDispatcher-worker-4 @coroutine#4> INFO  T[] U[] M[] - Redisson 'ktc:202505131307:expire-traffic-token-schedule-lock' unlocked.

문제의 코드

override suspend fun <R> lock(
    key: String,
    waitTime: Long,
    leaseTime: Long,
    timeUnit: TimeUnit,
    block: suspend () -> R
): R {
    val lock = redissonClient.getLock(key)
    return try {
        if (lock.tryLock(waitTime, leaseTime, timeUnit)) {
            block()
        } else {
            throw InternalServiceException(ErrorCode.REDISSON_LOCK_ATTEMPT_ERROR)
        }
    } finally {
        if (lock.isHeldByCurrentThread) {
            lock.unlock()
        }
    }
}

원인 분석

  • Redisson 락은 스레드 기반 동작 구조
  • 락을 획득한 스레드와 해제하는 스레드가 달라지면 unlock 실패 or unlock 미호출
  • Kotlin 코루틴은 suspend 함수 내에서 컨텍스트 전환이 일어나면, block 실행 시점과 unlock 시점의 스레드가 달라질 수 있음
  • 이로 인해 lock.isHeldByCurrentThread가 false가 되거나, IllegalMonitorStateException 예외 발생 가능
  • 비정상적으로 unlock 되지 않는 경우, Worker Thread 가 락 획득 시점과 block() 함수 처리된 후 스레드가 다름
-- 2. 비정상적으로 `unlock` 되는 경우
2025-05-13 13:05:00.008.DefaultDispatcher-worker-1 @coroutine#2> INFO  T[] U[] M[] - Redisson 'ktc:202505131305:expire-traffic-token-schedule-lock' locked.
2025-05-13 13:05:00.022.DefaultDispatcher-worker-4 @coroutine#2> INFO  T[] U[] M[] - Expired Traffic Token count : 0
-- 3. 비정상적으로 `unlock` 되는 경우
2025-05-13 13:06:00.012.DefaultDispatcher-worker-4 @coroutine#3> INFO  T[] U[] M[] - Redisson 'ktc:202505131306:expire-traffic-token-schedule-lock' locked.
2025-05-13 13:06:00.025.DefaultDispatcher-worker-1 @coroutine#3> INFO  T[] U[] M[] - Expired Traffic Token count : 0

Solution

  • lock() ~ unlock() 락 획득부터 해제까지 같은 스레드에서 실행 필요
  • 코루틴 컨텍스트를 withContext(Dispatchers.IO) 등으로 고정하여, 같은 코루틴 컨텍스트에서 실행되도록 코드 수정
override suspend fun <R> lock(
    key: String,
    waitTime: Long,
    leaseTime: Long,
    timeUnit: TimeUnit,
    block: suspend () -> R
): R = withContext(Dispatchers.IO) {
    val lock = redissonClient.getLock(key)
    try {
        if (lock.tryLock(waitTime, leaseTime, timeUnit)) {
            block()
        } else {
            throw InternalServiceException(ErrorCode.REDISSON_LOCK_ATTEMPT_ERROR)
        }
    } finally {
        if (lock.isHeldByCurrentThread) {
            lock.unlock()
        }
    }
}

2025-05-13 13:19:00.052.DefaultDispatcher-worker-2 @coroutine#1> INFO  T[] U[] M[] - Redisson 'ktc:202505131319:expire-traffic-token-schedule-lock' locked.
2025-05-13 13:19:00.113.DefaultDispatcher-worker-2 @coroutine#1> INFO  T[] U[] M[] - Expired Traffic Token count : 0
2025-05-13 13:19:00.121.DefaultDispatcher-worker-2 @coroutine#1> INFO  T[] U[] M[] - Redisson 'ktc:202505131319:expire-traffic-token-schedule-lock' unlocked.

2025-05-13 13:20:00.022.DefaultDispatcher-worker-3 @coroutine#2> INFO  T[] U[] M[] - Redisson 'ktc:202505131320:expire-traffic-token-schedule-lock' locked.
2025-05-13 13:20:00.036.DefaultDispatcher-worker-3 @coroutine#2> INFO  T[] U[] M[] - Expired Traffic Token count : 0
2025-05-13 13:20:00.039.DefaultDispatcher-worker-3 @coroutine#2> INFO  T[] U[] M[] - Redisson 'ktc:202505131320:expire-traffic-token-schedule-lock' unlocked.

2025-05-13 13:21:00.018.DefaultDispatcher-worker-1 @coroutine#3> INFO  T[] U[] M[] - Redisson 'ktc:202505131321:expire-traffic-token-schedule-lock' locked.
2025-05-13 13:21:00.030.DefaultDispatcher-worker-1 @coroutine#3> INFO  T[] U[] M[] - Expired Traffic Token count : 0
2025-05-13 13:21:00.032.DefaultDispatcher-worker-1 @coroutine#3> INFO  T[] U[] M[] - Redisson 'ktc:202505131321:expire-traffic-token-schedule-lock' unlocked.

Conclusion

  • Redisson 분산락과 같은 동일한 Thread 기반 컨텍스트 유지가 필요한 로직애소 코루틴 사용시 주의 필요
  • 코루틴 환경에서 같은 스레드에서 실행되도록 withContext(Dispatchers.IO) 로 컨텍스트 구분하도록 설정 필요