In my Android application, I have a usecase in which I need to run a bit of code inside a loop for as long as the app is running.

Example code:

  fun exampleRunCodeInLoop() {
    viewModelScope.launch(Dispatchers.Default) { 
      while (true) {
        delay(5000) // Wait for 5 seconds
        // @param someCondition is just an example for the if statement
        if (someCondition == true) {
          withContext(Dispatchers.Main) {
            // Do something on Main thread
          }
        }
      }
    }
  }

I am confused regarding which Dispatcher to use for the launch block to get the best performance. Should I use Default, IO or just run everything on Main?

CodePudding user response：

Dispatchers.Default as it is designed to be optimal for computations, by using a shared pool of threads that contains a maximum number of threads that is equal to the number of CPU cores

Dispatchers.IO in case your blocking the thread, waiting for a response without doing heavy computational logic

CodePudding user response：

At least here's the usage I did with coroutine dispatcher.

Dispatchers.Default - I usually use this when only doing CPU-intensive tasks to parallel with the current task on the main thread, it has a fixed size hardcoded to the number of available processors, because that's what makes sense for CPU-intensive tasks. Use with operation like loops, math operations, data/image manipulations.

Dispatchers.IO - is designed for offloading blocking IO tasks to a shared pool of threads. Use if you still need more threads than cores if you're doing blocking IO, e.g., Database query is an IO operation or network calls

Dispatchers.Main - A coroutine dispatcher that is confined to the Main thread operating with UI objects. This dispatcher can be used either directly or via MainScope factory. Usually such dispatcher is single-threaded. Usually used when you are done or finished with the background task from IO or Default to forecast whatever results from operations you've done to the UI or Main Thread.