Flutter multiple async methods for parrallel execution

Question

I'm still struggeling with the async/await pattern so I'm here to ask you some precisions.

I saw this page explaining the async/await pattern pretty well. I'm posting here the example that bother me :

import 'dart:async';  Future<String> firstAsync() async {   await Future<String>.delayed(const Duration(seconds: 2));   return "First!"; }  Future<String> secondAsync() async {   await Future<String>.delayed(const Duration(seconds: 2));   return "Second!"; }  Future<String> thirdAsync() async {   await Future<String>.delayed(const Duration(seconds: 2));   return "Third!"; }  void main() async {   var f = await firstAsync();   print(f);   var s = await secondAsync();   print(s);   var t = await thirdAsync();   print(t);   print('done'); } 

In this example, each async method is called one after another, so the execution time for the main function is 6 seconds (3 x 2 seconds). However, I don't understand what's the point of asynchronous function if they are executed one after another.

Are async functions not supposed to execute in the background ? Is it not the point of multiple async functions to fastens the process with parrallel execution ?

I think I'm missing something about asynchronous functions and async/await pattern in flutter so if you could explain me that, it would be very appreciated.

Best

Answer 1

Waiting on multiple Futures to complete using Future.wait() If the order of execution of the functions is not important, you can use Future.wait().

The functions get triggered in quick succession; when all of them complete with a value, Future.wait() returns a new Future. This Future completes with a list containing the values produced by each function.

Future     .wait([firstAsync(), secondAsync(), thirdAsyncC()])     .then((List responses) => chooseBestResponse(responses))     .catchError((e) => handleError(e)); 

or with async/await

try {     List responses = await Future.wait([firstAsync(), secondAsync(), thirdAsyncC()]); } catch (e) {     handleError(e) } 

If any of the invoked functions completes with an error, the Future returned by Future.wait() also completes with an error. Use catchError() to handle the error.

Resource:https://v1-dartlang-org.firebaseapp.com/tutorials/language/futures#waiting-on-multiple-futures-to-complete-using-futurewait