How to make "inappropriate blocking method call" appropriate?

Question

The warning is about methods that block current thread and coroutine cannot be properly suspended. This way, you lose all benefits of coroutines and downgrade to one job per thread again.

Each case should be handled in a different way. For suspendable http calls you can use ktor http client. But sometimes there is no library for your case, so you can either write your own solution or ignore this warning.

Edit: withContext(Dispatchers.IO) or some custom dispatcher can be used to workaround the problem. Thanks for the comments.

You also get this warning when calling a suspending function that is annotated with @Throws(IOException::class) (Kotlin 1.3.61). Not sure if that is intended or not. Anyway, you can suppress this warning by removing that annotation or changing it to Exception class.

Exceptions can occur that's why it shows this warning. Use runCatching{}. It catches any Throwable exception that was thrown from the block function execution and encapsulating it as a failure.

For Example:

 CoroutineScope(Dispatchers.IO).launch {
         runCatching{
               makeHttpRequest(URL(downloadLocation))
         }
}

Wrap the "inappropriate blocking method call" code in another context using withContext.

That is to say (for example):

If you are doing a read/write blocking method call:

val objects = withContext(Dispatchers.IO) { dao.getAll() }

If you are performing a blocking network request (using Retrofit):

val response = withContext(Dispatchers.IO) { call.execute() }

Or if you are performing a CPU intensive blocking task:

val sortedUsers = withContext(Dispatchers.Default) { users.sortByName() }

This will suspend the current coroutine, then execute the "inappropriate blocking call" on a different thread (from either the Dispatchers.IO or Dispatchers.Default pools), thereby not blocking the thread your coroutine is executing on.