Reentrant lock

Is reentrant lock for coroutines on the roadmap?

I’ve seen a discussion of it where a problem of coroutine identity was raised (https://github.com/Kotlin/kotlinx.coroutines/issues/965). But couldn’t a Job in the coroutine context be that identity?

[vklidu]

There is already a nice example of solution from Roman Elizarov here https://elizarov.medium.com/phantom-of-the-coroutine-afc63b03a131

suspend fun <T> Mutex.withReentrantLock(block: suspend () -> T): T {
  val key = ReentrantMutexContextKey(this)
  // call block directly when this mutex is already locked in the context
  if (coroutineContext[key] != null) return block()
  // otherwise add it to the context and lock the mutex
  return withContext(ReentrantMutexContextElement(key)) {
    withLock { block() }
  }
}

class ReentrantMutexContextElement(
  override val key: ReentrantMutexContextKey
) : CoroutineContext.Element

data class ReentrantMutexContextKey(
  val mutex: Mutex
) : CoroutineContext.Key<ReentrantMutexContextElement>

[elizarov]

IMO, not including reentrant mutex into the library so that you have to actually spend some time on copying the implementation of the reentrant mutex into your code and thinking on whether you really need it, works better than any @herebedragons annotation would.