Hi! Please help me understand why this hangs after printing 1,2,3 and how do I unfreeze it?... ``` ...

# coroutines

[dimsuz]

Hi! Please help me understand why this hangs after printing 1,2,3 and how do I unfreeze it?...

runBlocking {
    val events = BroadcastChannel<Int>(capacity = Channel.BUFFERED)
    merge(events.asFlow(), flowOf(1,2,3))
      .onStart { events.offer(42) }
      .take(4)
      .collect {
        println("received $it")
      }
  }

This popped up while I was trying to write a unit test for a certain api and got me puzzled. It looks like event should be buffered in a non-blocking way.
I also use .take(4) to unsubscribe from hot Flow, but it's that 42 never gets seen somehow.

[bezrukov]

Because onStart is called before subscribing to flow. So you offered an element to channel before subscribing to it. Buffered broadcast channel doesn`t replay last element, so 42 is just lost

[dimsuz]

thanks!

[dimsuz]

I managed to reproduce my problem more closely. This prints only "received 1" and never receives 42 , hangs. It seems that scan is somehow involved:

runBlocking {
    val events = BroadcastChannel<Int>(capacity = Channel.BUFFERED)
    events.asFlow()
      .scan(1, { accumulator, value -> value })
      .take(2)
      .collect {
        println("received $it")
        if (it == 1) {
          events.offer(42)
        }
      }
  }