If I have a resource inside a `Flow` , what’s the ...

# coroutines

[spierce7]

If I have a resource inside a Flow , what’s the best way to call something when the context it’s running in is cancelled? i.e. when the flow is cancelled, I need to call `process.destroy()`:

actual fun run(command: String): Flow<String> = flow {
        val split = command.split(' ')
        val process = ProcessBuilder(split).apply {
            redirectErrorStream(true)
        }.start()

        process.inputStream.source().use { processSource ->
            processSource.buffer().use { bufferedProcessSource ->
                while (true) {
                    val line = bufferedProcessSource.readUtf8Line() ?: break
                    emit(line)
                }
            }
        }
    }.flowOn(<http://Dispatchers.IO|Dispatchers.IO>)

[bezrukov]

You can use currentCoroutineContext from flow {} for checking if it still active

[bezrukov]

So you can simply switch from while(true) to while (currentCoroutineContext().isActive). Also, I believe emit will throw cancellation exception if flow's collector was cancelled (since 1.3.7). Then you can call process.destroy() in finally block

[bezrukov]

https://github.com/Kotlin/kotlinx.coroutines/issues/2026 more details

[spierce7]

Thanks for the advise. This looks good.

[spierce7]

Is there any difference between currentCoroutineContext() and coroutineContext? It doesn’t look like it

[spierce7]

it’s hard to be sure with compiler magic implicit variables like this though.

[bezrukov]

yes, there is a difference, sometimes coroutineContext may be ambiguous - in case if you have an access to CoroutineScope as this (e.g. if you write flow { } inside `coroutineScope`/`launch`/`async` etc or if you write the flow operator as an extension function of CoroutineScope, or something like that). There is an example in the link I mentioned where coroutineContext will refer to the wrong context.