Solution: Using dispatchers

createInvoice does not need to set a dispatcher because postInvoice is a suspending function that does not block threads.

sendEmail needs to set the dispatcher to Dispatchers.IO or a custom dispatcher with a thread limit because api is a blocking function.

getUserOrders does not need to set a dispatcher because toList is a suspending function that does not block threads.

upscaleImage needs to set the dispatcher to Dispatchers.Default or Dispatchers.Default limited to a certain number of threads because upscaling an image is a CPU-intensive operation.

The author:

Marcin Moskała

Marcin Moskala is a highly experienced developer and Kotlin instructor as the founder of Kt. Academy, an official JetBrains partner specializing in Kotlin training, Google Developers Expert, known for his significant contributions to the Kotlin community. Moskala is the author of several widely recognized books, including "Effective Kotlin," "Kotlin Coroutines," "Functional Kotlin," "Advanced Kotlin," "Kotlin Essentials," and "Android Development with Kotlin."

Beyond his literary achievements, Moskala is the author of the largest Medium publication dedicated to Kotlin. As a respected speaker, he has been invited to share his insights at numerous programming conferences, including events such as Droidcon and the prestigious Kotlin Conf, the premier conference dedicated to the Kotlin programming language.