Isolates and Event Loops – Flutter

person shubham sharmafolder_openFlutterlocal_offeraccess_time February 18, 2024

Isolates in Flutter

In Flutter, isolates are a feature of the Dart language, which Flutter is built on. Isolates allow for concurrent execution of Dart code, enabling tasks to run in parallel without blocking the main UI thread.

How many Isolates Flutter have in default

In Flutter, by default, there is a single UI isolate where all the UI rendering and event handling occur. Additionally, there is a single main isolate where the Dart code runs.

So, in total, Flutter has two isolates by default: the UI isolate and the main isolate.

Isolates are Dart’s way of achieving concurrency, where each isolate has its own memory heap and runs in parallel with other isolates. This allows Flutter to perform tasks concurrently without blocking the UI. However, it’s worth noting that Flutter also supports spawning additional isolates for background tasks or heavy computations using the compute() function or the Isolate class.

How to create new one

To create a new isolate in Dart, you can use the Isolate.spawn function. Here’s how you can do it:

In this example:

  • myIsolateFunction is a function that will be executed in the new isolate.
  • Isolate.spawn takes the function to be executed in the new isolate (myIsolateFunction) and an optional message parameter. The message parameter can be used to pass data to the new isolate.
  • You can also pass arguments to the spawned function by adding them after the function name in the spawn call. For example: Isolate.spawn(myIsolateFunction, 'Hello from main!');

When you run the code, you will see output from both the main isolate and the new isolate:

Keep in mind that isolates are fully isolated from each other, meaning they have their own memory heap and run concurrently. Therefore, they cannot directly share data with each other. If you need to communicate between isolates, you can use message passing or other inter-isolate communication mechanisms provided by Dart, such as SendPort and ReceivePort.

Can we same resource (variable) in different isolets

No, isolates in Dart are fully isolated from each other, meaning they have their own memory heap and cannot directly share resources like variables. Each isolate runs in its own Dart VM (Virtual Machine), and there is no shared memory between isolates by default.

However, Dart provides mechanisms for inter-isolate communication, such as message passing using SendPort and ReceivePort, which allows isolates to communicate with each other by sending messages. This means you can send data from one isolate to another, but you cannot directly access or share variables between isolates.

Here’s a basic example of sending and receiving messages between isolates using SendPort and ReceivePort:

In this example, the main isolate creates a new isolate using Isolate.spawn, then sends a message to the new isolate. The new isolate receives the message and prints it. The communication between isolates is achieved through SendPort and ReceivePort.

What is event loop?

The event loop is a fundamental concept in asynchronous programming that manages the execution of tasks and events in a single-threaded environment. It’s commonly used in programming languages like JavaScript, Dart (used in Flutter), Python, and many others.

Here’s how the event loop works:

  1. Single Thread: In environments with an event loop, such as web browsers, Node.js, or Dart VM, there is typically a single execution thread. This means that all code execution happens on this single thread.
  2. Non-Blocking I/O: When an asynchronous operation, such as reading from a file or making a network request, is initiated, the event loop doesn’t wait for the operation to complete. Instead, it registers a callback function to be executed once the operation finishes, and then continues to process other tasks.
  3. Event Queue: Asynchronous operations and events are placed in an event queue, which the event loop continuously checks. When the event loop detects that the execution stack is empty (i.e., there are no more synchronous tasks to execute), it dequeues tasks from the event queue and executes them one by one.
  4. Callbacks: When an asynchronous operation completes, its corresponding callback function is placed in the event queue. The event loop picks up this callback and executes it when it reaches the top of the event queue.
  5. Concurrency: While the event loop is single-threaded, asynchronous operations and events can still be processed concurrently. This allows programs to remain responsive and handle multiple tasks simultaneously without blocking the main execution thread.

In summary, the event loop is responsible for managing the execution of asynchronous tasks and events in a single-threaded environment, ensuring that tasks are executed in the correct order and without blocking the main thread. It’s a crucial component of asynchronous programming models and is essential for building responsive and efficient applications.


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