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Cliabhach/cat.dart

Last active May 2, 2022 07:50
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Testing out interaction between Dart Futures and Dart Isolates
Raw
cat.dart
/// SPDX-License-Identifier: Apache-2.0
/// Based on source code in https://levelup.gitconnected.com/fluttering-dart-futures-and-isolates-6b4bce6d804b
import 'dart:math';
import 'dart:isolate';
class Cat {
var index;
var meowDelay;
Cat(int index, int meowDelay) {
this.index = index;
this.meowDelay = meowDelay;
}
/// Wait a given number of seconds, meow, and then run `afterMeow`.
void meow(Future<void> afterMeow) async {
await Future.delayed(Duration(seconds: meowDelay));
print('Kitten $index: Meow!');
await afterMeow;
print('Kitten $index has finished.');
}
}
Future<void> createMeowFuture(int index) async {
return print('Just meowed! ($index/10)');
}
void main() async {
final timeInterval = 10;
final random = Random.secure();
// Request 10 meows.
await doLoop(random, timeInterval);
// TODO: Wait for all of those meows to finish
print('Just finished!!');
}
/// Correct
// Kitten 0: Meow!
// Just meowed! (0/10)
// Kitten 1: Meow!
// Just meowed! (1/10)
// Kitten 2: Meow!
// Kitten 3: Meow!
// Just meowed! (2/10)
// Kitten 4: Meow!
// Kitten 5: Meow!
// Just meowed! (3/10)
// Kitten 6: Meow!
// Kitten 7: Meow!
// Just meowed! (4/10)
// Just meowed! (5/10)
// Kitten 8: Meow!
// Kitten 9: Meow!
// Just meowed! (6/10)
// Just meowed! (7/10)
// Just meowed! (8/10)
// Just meowed! (9/10)
// Just finished!!
/// Incorrect
// Just meowed! (0/10)
// Just meowed! (1/10)
// Just meowed! (2/10)
// Just meowed! (3/10)
// Just meowed! (4/10)
// Just meowed! (5/10)
// Just meowed! (6/10)
// Just meowed! (7/10)
// Just meowed! (8/10)
// Just meowed! (9/10)
// Just finished!!
Future<void> doLoop(Random random, int timeInterval) async {
for(var i=0; i<10; i++) {
final kitten = Cat(i, random.nextInt(timeInterval));
await Isolate.spawn(kitten.meow, createMeowFuture(i));
}
}
@Cliabhach
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Cliabhach commented May 2, 2022

The problem I have, is that waiting for Isolate.spawn only waits until kitten.meow is called. I want to return (on line 37) only when all of the print statements have occurred.

@dinakar-m
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dinakar-m commented May 2, 2022 

Create a new isolate using Isolate.spawn()
Let’s look at some Flutter isolate examples. The first way to create an isolate is by using the Isolate.spawn() call. We pass in the method we want to run as the first parameter, while the second argument is the parameter we want to pass to the isolate.

The function passed to the isolate spawn() must be a top-level function *(a function that is not within the boundary of a class) or a static method.

Here’s the code to create an isolate.

here it is explaining well... may be you want to achieve your objective just by different way?
https://blog.codemagic.io/understanding-flutter-isolates/

@dinakar-m
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dinakar-m commented May 2, 2022

@Cliabhach below is just idea... i dont know if help or not!

i think this is just basic problem about

  1. Run multiple threads by child or by multiple thread...
  2. After point 1. completes know the by call back (await etc.)

try understanding the below part code....
https://itnext.io/minimalist-guide-to-isolates-in-dart-flutter-dd5bdee031e
image

one more idea in your case you should understand how and why you want spawn is there is better design you can write your code..

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