class ResourceLocker {

    private val lockedResourceContext = Executors
        .newSingleThreadExecutor()
        .asCoroutineDispatcher()

    private val lockedResources = mutableSetOf<Long>()

    suspend fun getLock(resId: Long, action: suspend () -> Unit) {
        // actually get lock
        withContext(lockedResourceContext) {
            suspendUntilLockAcquired(resId)
        }

        //locked, so nothing else can touch it.
        action()

        // release lock
        withContext(lockedResourceContext) {
            lockedResources.remove(resId)
        }
    }

    private tailrec suspend fun suspendUntilLockAcquired(resId: Long) {
        when (lockedResources.contains(resId)) {
            true -> lockedResources.add(resId)
            false -> {
                delay(25)
                suspendUntilLockAcquired(resId)
            }
        }
    }
}