hey, I want to make a blocking function to suspend...

# coroutines

[kurt_steiner]

hey, I want to make a blocking function to suspend function, I have tried this code

suspend fun mydelay(timeMillis: Long) {
        if (timeMillis < 0) {
            return
        }

        if (timeMillis < Long.MAX_VALUE) {
            suspendCoroutine<Unit> {
                Thread.sleep(timeMillis)
                it.resume(Unit)
            }
        }
    }

but failed in

repeat(100) {
            launch {
                mydelay(1000)
                println("awake ${Thread.currentThread()}")
            }
        }

it can be like delay suspend function, how can I do it ?

[Ahmed]

What exactly do you want to achieve?

If you only want to make a function suspend, I am assuming it does IO, you can do that with

suspend fun doIO() = withContext(<http://Dispatchers.IO|Dispatchers.IO>) { /* code here */ }

// If it’s something you want the result for at later in time the you can use async {} and then call .await() on it

[kurt_steiner]

actually, here I have a sync function called download, and I want to make it suspend so that I can launch many coroutines with running it

repeat(1000) {
    download
}

so I similator it with Thread.sleep

[Zach Klippenstein (he/him) [MOD]]

I think the best practice here is to just launch your coroutines from your loop without any additional context, then switching to the IO dispatcher (via withContext) should be an implementation detail of your download function. The reason is that the download function could potentially use a non-blocking api itself, which wouldn’t require switching dispatchers. If it uses a blocking api, that’s an implementation detail and the function can satisfy the “suspend functions must not block caller” contract by switching dispatchers.

[kurt_steiner]

heavy sigh. is there a async downloader with kotlin coroutine ? I want to check the code

[Zach Klippenstein (he/him) [MOD]]

There are tons of examples of doing various types of io with coroutines on the internet, this is a pretty common thing.

[kurt_steiner]

I don't know what's the keyword to search, may be you can help me

[Zach Klippenstein (he/him) [MOD]]

I’m not either, you’re asking a pretty general question. The thing I suggested is basically just this, adapting the code you’ve already posted:

suspend fun downloadEverything() {
  coroutineScope {
    repeat(1000) {
      launch { download() }
    }
  }
}

suspend fun download() {
  withContext(Dispatchers.IO) {
    blockingDownloadCall()
  }
}