The idea of single threaded execution in Kotlin Coroutine.

single-coroutine-executor.kt

private val semaphore = AtomicBoolean(false)

private suspend fun Service.checkAndRefreshAccessToken() {
  val aSecond = 1000L
  var mills = 1L
  // wait (binary-) semaphore to ensure only one coroutine
  // executing this function's try ... catch body.
  while (!semaphore.compareAndSet(false, true)) {
    delay(millis)
    mills = minOf(aSecond, millis * 2)
  }

  try {
    // update token, if it will be expired soon.
    if (token.expiresIn(10 * aSecond)) {
      token.refresh() // NOTE: This is suspend function
    }
  } finally {
    // signal semaphore.
    semaphore.lazySet(false)
  }
}