What methods can be used to organize simultaneous query execution without using threads and asynchronous functions?

To perform multiple requests simultaneously without using threads (Threads) and asynchronous functions (async/await) in Android, you can apply the following methods:

1. Using RxJava — a library for reactive programming that allows running multiple requests in parallel and processing their results.

2. Using Handler and Looper — you can send tasks to the message queue for sequential or delayed execution, which prevents blocking the main thread.

3. Using ExecutorService with a thread pool — although related to threads, it allows managing task execution without explicitly creating threads.

4. Using libraries for parallel execution, such as Retrofit with enqueue() support — enables performing network requests in the background without explicitly creating threads.

5. Using Kotlin Coroutines launched in GlobalScope.launch without async — although this is asynchronous, it allows launching coroutines for parallel work without using async/await.

If strictly excluding threads and asynchronous functions, you can use Callback-oriented APIs that manage background execution themselves, such as network libraries with callbacks.

Example with Retrofit:

val call = apiService.getData()
call.enqueue(object : Callback<Data> {
    override fun onResponse(call: Call<Data>, response: Response<Data>) {
        // handle successful response
    }

    override fun onFailure(call: Call<Data>, t: Throwable) {
        // handle error
    }
})

Thus, requests are executed in parallel without explicitly using threads or async/await.