queue 2.0.6

Queue up futures from multiple sources and await their return anywhere in your code.

queue

Easily queue futures and await their values.

This library allows you to send a future to central queue. The queue will execute the futures in the order they are queued and once the future is complete it will return its result.

My use case was to rate limit calls to bluetooth devices. There were multiple bluetooth devices connected that may have different commands being sent from lots of areas in the app. The devices were tripping over themselves and not responding. A stream wasn't the appropriate tool as I needed to get the result back. Hence a library was born.

Alternative use cases could be spidering a website, downloading a number of files, or rate limiting calls to an API.

Usage

The most simple example:

import 'package:dart_queue/dart_queue.dart';

main() async {
  final queue = Queue();

  //Queue up a future and await its result
  final result = await queue.add(()=>Future.delayed(Duration(milliseconds: 10)));

  //Thats it!
}

A proof of concept:

import 'package:dart_queue/dart_queue.dart';

main() async {
  //Create the queue container
  final Queue queue = Queue(delay: Duration(milliseconds: 10));
  
  //Add items to the queue asyncroniously
  queue.add(()=>Future.delayed(Duration(milliseconds: 100)));
  queue.add(()=>Future.delayed(Duration(milliseconds: 10)));
  
  //Get a result from the future in line with await
  final result = await queue.add(() async {
    await Future.delayed(Duration(milliseconds: 1));
    return "Future Complete";
  });
  
  //100, 10, 1 will reslove in that order.
  result == "Future Complete"; //true
}

Parallel processing

This doesn't work in batches and will fire the next item as soon as as there is space in the queue Use [Queue(delayed: ...)] to specify a delay before firing the next item

import 'package:dart_queue/dart_queue.dart';

main() async {
  final queue = Queue(parallel: 2);

  //Queue up a future and await its result
  final result1 = await queue.add(()=>Future.delayed(Duration(milliseconds: 10)));
  final result2 = await queue.add(()=>Future.delayed(Duration(milliseconds: 10)));

  //Thats it!
}

On complete

import 'package:dart_queue/dart_queue.dart';

main() async {
  final queue = Queue(parallel: 2);

  //Queue up a couple of futures
  queue.add(()=>Future.delayed(Duration(milliseconds: 10)));
  queue.add(()=>Future.delayed(Duration(milliseconds: 10)));


  // Will only resolve when all the queue items have resolved.
  await queue.onComplete;
}

Rate limiting

You can specify a delay before the next item is fired as per the following example:

import 'package:dart_queue/dart_queue.dart';

main() async {
  final queue = Queue(delay: Duration(milliseconds: 500)); // Set the delay here

  //Queue up a future and await its result
  final result1 = await queue.add(()=>Future.delayed(Duration(milliseconds: 10)));
  final result2 = await queue.add(()=>Future.delayed(Duration(milliseconds: 10)));

  //Thats it!
}

Contributing

Pull requests are welcome. There is a shell script ci_checks.sh that will run the checks to get past CI and also format the code before committing. If that all passes your PR will likely be accepted.

Please write tests to cover your new feature.