Barrier

The Barrier design pattern provides us with the ability to wait for multiple concurrent tasks to complete before proceeding further. A common use case for this is composing objects from different sources.

For example, take the following class:

data class FavoriteCharacter(
    val name: String,
    val catchphrase: String,
    val picture: ByteArray = Random.nextBytes(42)
)

Let's assume that the catchphrase data comes from one service and the picture data comes from another. We would like to fetch these two pieces of data concurrently:

fun CoroutineScope.getCatchphraseAsync
(
    characterName: String
) = async { … }
fun CoroutineScope.getPicture
(
    characterName: String
) = async { … }

The most basic way to implement concurrent fetching would be as follows:

suspend fun fetchFavoriteCharacter(name: String) = coroutineScope {
  ...