Microtasks and Event Loops in Dart#

About#

Microtasks and the Event Loop are essential components in Dart for managing asynchronous operations efficiently. They ensure that tasks are executed in a responsive and non-blocking manner.

Information#

• Event Loop: Coordinates the execution of tasks from two main queues:

  • Microtask Queue: High-priority tasks that run immediately after the current code but before other events.
  • Event Queue: Handles less urgent tasks like I/O and timers after all microtasks are processed.

• Microtasks: Small tasks scheduled to run as soon as possible after the current code. They handle operations such as Future completions and quick updates.

Use#

Microtasks are used for immediate task execution, such as:

• Completing Future callbacks.
• Performing rapid updates or animations.
• Handling critical data in real-time applications.

Example#

void main() {
  print('Start');

  // Schedule a microtask
  scheduleMicrotask(() {
    print('Microtask 1');
  });

  // Schedule another microtask
  scheduleMicrotask(() {
    print('Microtask 2');
  });

  // Schedule a future
  Future(() {
    print('Future 1');
  });

  // Schedule another future
  Future(() {
    print('Future 2');
  });

  // Add another microtask after synchronous code
  scheduleMicrotask(() {
    print('Microtask 3');
  });

  print('End');
}

Overall#

Understanding Microtasks and the Event Loop is crucial for managing asynchronous operations effectively in Dart. These concepts ensure that tasks are handled in a responsive and non-blocking manner, contributing to a smooth user experience in Dart applications.

Microtasks#

• Definition: Microtasks are tasks that are scheduled to run as soon as possible after the currently executing code but before any other events in the Event Queue. They are ideal for operations that need immediate execution, such as handling Future completions or updating state.

• Scheduling: Microtasks are scheduled using the scheduleMicrotask function. They have a higher priority than tasks in the Event Queue, ensuring they are executed first.

• Use Cases: Common use cases for microtasks include:

  • Completing Future callbacks.
  • Performing quick updates or animations.
  • Handling critical data that needs prompt processing.

Event Loop#

• Definition: The Event Loop is responsible for managing and scheduling tasks from the Microtask Queue and the Event Queue. It ensures that tasks are executed in the correct order, maintaining application responsiveness.

• Queues:

  • Microtask Queue: Holds high-priority tasks that are executed immediately after the current code but before other events.
  • Event Queue: Manages less urgent tasks, such as I/O operations and timers, processed after all microtasks are completed.

• Execution Order: The Event Loop processes tasks in the following order:

  1. Microtasks are executed first, ensuring immediate execution of high-priority tasks.
  2. Event Queue tasks are executed next, such as handling I/O operations or timers.

Example#

Here’s a simple example demonstrating the execution order of microtasks and futures:

void main() {
  print('Start');

  // Schedule microtasks
  scheduleMicrotask(() {
    print('Microtask 1');
  });

  // Schedule another microtask
  scheduleMicrotask(() {
    print('Microtask 2');
  });

  // Schedule a future with a delay
  Future.delayed(Duration(seconds: 1), () {
    print('Future 1');
  });

  // Schedule another future with a delay
  Future.delayed(Duration(seconds: 2), () {
    print('Future 2');
  });

  // Additional microtask
  scheduleMicrotask(() {
    print('Microtask 3');
  });

  print('End');
}

• Microtasks are high-priority tasks executed immediately after current synchronous code, before other events.
• Event Loop processes tasks from the Microtask Queue first, then the Event Queue.
• Microtasks are used for quick operations like handling Future callbacks.
• Example: Microtasks run before futures, ensuring immediate task execution.