Isolates in Flutter | Dart Isolate Tutorial — Run tasks in background using Isolates

Vijay R
vijaycreations
Published in
4 min readMay 29, 2023

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In this article we will discuss about when, why and how to use isolates in Flutter apps.

🎥 Video Tutorial

🔭 Implementation

Just like threads what we have in java, we have isolates here in flutter. Each isolate has its own memory where it performs the event looping. So in general isolates are individual worker components that can do the given task without affecting the main dart engine. Since dart language is single threaded, isolates can be used for achieving multi-threading in flutter apps.

So this is what isolate technically is.

Now let’s turn our attention towards the question,
Why do we need to use isolates in our flutter app?

Lets try to answer this question with the help of a simple example. Consider we the basic UI containing a circularProgressIndicator and Elevated button widgets placed at the center of our app screen as shown below👇.

 Scaffold(
appBar: AppBar(title: const Text('Isolates')),
body: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: [
const CircularProgressIndicator(),
const SizedBox(height: 50),
ElevatedButton(
child: const Text('Run Heavy Task'),
onPressed: () => runHeavyTaskWithOutIsolate(4000000000),
),
],
),
),
);

In the above code snippet, we try to call runHeavyTaskWithOutIsolate() method which by it’s name is going to perform a heavy duty task without using isolate (it can be file operation, network related work etc.,) which depends on our use-case.

In this article, to keep it simple we will make use of basic for loop that will iterate for 4000000000 (which is passed as a parameter).

The runHeavyTaskWithOutIsolate() method is as follows.,

int runHeavyTaskWithOutIsolate(int count) {
int value = 0;
for (var i = 0; i < count; i++) {
value += i;
}
print(value);
return value;
}

Now if we run our app, we will notice that upon clicking the button (which calls the runHeavyTaskWithOutIsolate() method) the circularProgressIndicator widget that was loading infinitely, gets stuck and freezes until the for loop completes it’s execution.

This clearly says us that, since dart is single threaded language, the main thread is busy executing the 4000000000 (4 billion) iterations. so it has no time to refresh the UI components. Once the heavy task (4 billion) iteration is complete, the main thread or the main isolate turns its focus to the UI thereby refreshing back to its original state where we will be able to observe the circularProgressIndicator getting loaded back again.

So this is a typical example, where the isolate needs to be used. Hence now let’s try using isolate for performing the same heavy task and see if our circularProgressIndicator is getting stuck at any point of time. Therefore our previous code needs to be updated as follows.,

Scaffold(
appBar: AppBar(title: const Text('Isolates')),
body: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: [
const CircularProgressIndicator(),
const SizedBox(height: 50),
ElevatedButton(
child: const Text('Run Heavy Task'),
onPressed: () => useIsolate(),
),
],
),
),
);

The useIsolate() methods which is called inside the onpress event is as follows,

useIsolate() async {
final ReceivePort receivePort = ReceivePort();
try {
await Isolate.spawn(
runHeavyTaskIWithIsolate, [receivePort.sendPort, 4000000000]);
} on Object {
debugPrint('Isolate Failed');
receivePort.close();
}
final response = await receivePort.first;

print('Result: $response');
}

int runHeavyTaskIWithIsolate(List<dynamic> args) {
SendPort resultPort = args[0];
int value = 0;
for (var i = 0; i < args[1]; i++) {
value += i;
}
I

Here in the above code we have made use of isolates to perform the same task. Wherein we use the Isolate.spawn() method and pass in the function that is going to perform the heavy task followed by the arguments if any.

Additionally, we make use of the PORTS (Send and receive ports) to pass the data between isolates.

Now if we run our app, we will notice that the CircularProgressIndicator widget that was getting freezed earlier won’t get affected now. Because we have now added the isolate to perform the heavy task, so it can run independently to do the computation without affecting the main dart thread.

Well that’s it. 🎉 Run the code to see it in action.🥳

Refer my video tutorial for complete guide:👉 https://www.youtube.com/watch?v=g6sPAWCFgtE

Get the complete source code here:👉 https://github.com/vijayinyoutube/isolates_demo

Check out all my Flutter related blogs here.,👇

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Vijay R
vijaycreations

Hai👋 I’m a flutter developer experienced in designing and developing stunning mobile apps. Reach out for freelance projects: calico.takeoff_01@icloud.com