Unlocking Concurrency in Flutter: A Deep Dive into Isolates
When it comes to building cross-platform apps that run seamlessly across multiple devices and ecosystems, Flutter is an excellent choice. However, to achieve this, developers need to tackle complex tasks like fetching data from the network, serializing it, and displaying the result in a user-friendly interface. To avoid performance bottlenecks, it’s essential to understand how to leverage multithreading in Flutter to run tasks in the background and keep the main thread free.
Concurrency vs. Asynchrony in Flutter
In Flutter, you can introduce asynchronous behavior using async/await functions and Stream APIs. However, the concurrency of your code depends on the underlying threading infrastructure provided by Flutter. To understand how Flutter handles concurrency, let’s explore its threading infrastructure.
Understanding Flutter’s Threading Infrastructure
Flutter maintains a set of thread pools at the VM level, which are used for tasks like Network I/O. Instead of exposing threads, Flutter provides a different concurrency primitive called isolates. The entire UI and most of your code run on what’s called the root isolate.
What are Flutter Isolates?
An isolate is an abstraction on top of threads, similar to an event loop, with a few key differences:
- An isolate has its own memory space
- It cannot share mutable values with other isolates
- Any data transmitted between isolates is duplicated
An isolate is designed to run independently of other isolates, offering benefits like easier garbage collection. When creating parent isolates that spawn child isolates, remember that the child isolates will terminate if the parent does.
Creating Isolates in Flutter
There are two ways to create isolates in Flutter: using the compute function and using Isolate.spawn.
Method 1: Using Compute
The compute function is a convenient way to execute code in a different isolate and return the results to the main isolate. Let’s say we have a class called Person, which we want to deserialize from a JSON object. We can add the deserializing code as follows:
Method 2: Using Isolate.spawn
This method is a more elementary way to work with isolates. Here’s what our deserialization code looks like:
Reusing Flutter Isolates
While the previous example is best used for single-shot tasks, we can easily reuse the isolate by setting up bidirectional communication and sending more data to deserialize while listening to the port stream for the results.
Exploring the flutter_isolate Package
The flutter_isolate package offers utility tools to help achieve isolate reusability. One of the most useful is the LoadBalancer API, which lets us create and manage a pool of isolates. This class automatically delegates tasks to free isolates when it receives them.
Integrating Isolates with Stream APIs
Flutter provides an asyncMap operator to integrate our existing streams with isolates. This allows us to hook up a load-balanced isolate to run code in the background, similar to how we’d switch threads in reactive programming.
Flutter Isolate Best Practices
While it may seem beneficial to create as many isolates as we want, spawning isolates comes with a cost that varies across devices. It’s essential to understand that isolates work wonderfully for tasks like image manipulation, but the cost sometimes can’t be justified for simpler use cases.
By following these best practices and understanding how to leverage multithreading in Flutter, you can build high-performance apps that run smoothly across multiple devices and ecosystems.