AsyncQueue

AsyncQueue is a TypeScript class that provides a simple asynchronous queue implementation. It implements the Symbol.asyncIterator interface, allowing it to be used in for-await-of loops. This enables one or multiple consumers to process items in the queue asynchronously.

Installation

Install AsyncQueue using npm:

npm install @ai-zen/async-queue

Usage

Importing

1import AsyncQueue from "@ai-zen/async-queue";

Creating an AsyncQueue Instance

1const queue = new AsyncQueue([1, 2, 3]);

Pushing Values to the Queue

1queue.push(value);
2
3// Or
4queue.push(value1, value2, value3, ...);
5
6// Or
7queue.push(...values);

The push method adds one or more values to the queue, and increases its size.

Marking the Queue as Done

1queue.done();

The done method marks the queue as finished. This indicates that no more items will be added to the queue.

Iterating Over the Queue

1for await (const value of queue) {
2  // Consume the value
3}

The for await...of loop can be used to iterate over the items in the queue. This loop is asynchronous and will wait for each value to be available before consuming it.

Getting the Size of the Queue

1const size = queue.size;

The size property returns the current size of the queue.

Examples

Example 1: Single Consumer

You can add data asynchronously while consuming data asynchronously.

1const queue = new AsyncQueue();
2
3(async () => {
4  for (const value of [1, 2, 3, 4, 5]) {
5    await sleep(1); // Simulate asynchronous operations
6    queue.push(value);
7  }
8  queue.done();
9})();
10
11for await (const value of queue) {
12  await sleep(1); // Simulate asynchronous operations
13  console.log(value);
14}
15
16console.log("Done!");

Output:

1
2
3
4
5
Done!

Example 2: Multiple Consumers

This is useful for limiting the number of concurrent operations, such as network requests.

1// Assume `Task` and `TaskResult` are types defined elsewhere in your code
2const queue = new AsyncQueue<Task>(tasks);
3
4queue.done();
5
6const results: TaskResult[] = [];
7
8// Start 10 concurrent consumers using the competing-consumers pattern
9await Promise.all(
10  Array.from({ length: 10 }).map(async () => {
11    for await (const task of queue) {
12      try {
13        const result = await download(task); // Perform the task
14        results.push(result);
15      } catch (error) {
16        console.error("Task failed:", error);
17      }
18    }
19  })
20);

Example 3: Backpressure

The library provides a very simple backpressure control mechanism that can prevent the queue length from exceeding a threshold. Just call and wait for the backpressure method before push. If the queue reaches the threshold, the backpressure method will wait until the queue length decreases to have space.

1const queue = new AsyncQueue<number>();
2const result: number[] = [];
3
4(async () => {
5  for (const value of Array.from({ length: 100 }).map((_, i) => i)) {
6    await queue.backpressure(10); // Wait for the queue to have space, the maximum size is 10
7    queue.push(value);
8  }
9  queue.done();
10})();
11
12for await (const value of queue) {
13  await sleep(1000); // Simulate asynchronous operations
14  result.push(value);
15}

License

This package is licensed under the MIT License.