I want to display an image for 3 seconds while also fetching, serializing and persisting a large JSO...

# coroutines

[Stanley Gomes]

I want to display an image for 3 seconds while also fetching, serializing and persisting a large JSON blob. Keeping in mind the whole operation could take more than 3 seconds on slow network, this is what I have right now

viewmodelScope.launch {
      val deferredFetchAndPersist = async {
          some suspend fun()
      }
      val deferredTimer = async {
          delay(3000)
      }
      awaitAll(deferredFetchAndPersist, deferredTimer)

      hideImageView()
   }

This works but I feel it's a little too verbose. Is there a better way I can achieve this?
Thanks

[Erik]

What if the operation takes less than 3 seconds? Right now you'd also await the timer for 3 seconds anyways. If that's not what you want, then cancel the timer on completion of the operation.

And do you intend to show the image for more than 3 seconds if the operation takes more than that?

Other than that this seems fine.

[Stanley Gomes]

The requirement is to show the image for at least 3 seconds and yes for your 2nd question.
If this seems fine then thanks!

[uli]

looks fine to me. You could also use coroutineScope { … } and use launch instead of `async`and awaitAll

[uli]

viewmodelScope.launch {
    coroutineScope {
      launch {
          fetchAndPersist()
      }
      launch {
          delay(3000)
      }
    }
    hideImageView()
   }

[uli]

Well, actually you should use launch if you don’t expect a result. When structured concurrency does not come handy you can also joinAll the `Job`s returned from launch instead of calling `awaitAll`on the `Deferred<Unit>`s

[bezrukov]

another option would be to write it in sequential way, which is probably looks simpler in this particular case.

delay(3000 - measureTimeMillis {
    yourSuspendFun()
})
hideImageView()

(delay works fine with negative arguments, so everything should work regardless if yourSuspendFun faster/slower than 3s)

[Erik]

Wow, that's pretty effective and pretty difficult to understand as a reader! 👏 But that's arguable!

[Erik]

Maybe actually write it sequentially, on multiple lines and optionally with named values, to increase readability?

val actualMillis = measureTimeMillis { yourSuspendFun() }
val minimumMillis = 3000
delay(minimumMillis - actualMillis)
hideImageView()

[Stanley Gomes]

I like it! Thanks for all the suggestions everyone 🙏