crs_queue

crs_queue is a simple coalescing, rate-limited, serializable/deserializable task queue for Node and Deno which is designed for issuing requests to a rate-limited endpoint from a host program that is transient (as opposed to long-running).

Features

• Tasks with the same (string) identity are coalesced (using "last writer wins" for task data)
• Requests are limited according to a user-specified rate
• The entire queue (including tasks, data, history) can be serialized/deserialized (e.g. to localStorage)
• Tasks can be delayed/scheduled for the future

Note that this library does not guarantee that requests won't be issued more than once. For example, if the queue is serialized while a request is in flight, that request can later be run a second time if the queue is deserialized and restarted.

API

Task type

Tasks are objects with only primitive/JSON-compatible properties. There is only one required property:

• id (string): This is the identity of the task; tasks with the same identity are coalesced (with all other data being overwritten by the most recent task)

Example:

{
    id: "update leaderboard",
    value: 5,
}

TaskManager

This section is just a quick summary. Refer to JSDoc comments for more detail.

The task queue is encapsulated in the TaskManager<TTask extends TaskBase, TResult> class. The class constructor takes options object with the following properties:

• rateLimit ({ count: number, periodMS: number}):
  • count: Maximum number of tasks to process during the period
  • periodMS: Length of the period in milliseconds
• onRunTask ((task: TTask) => Promise<TResult>): Async callback for processing a task
• onTaskFailure ((task: TTask) => void | undefined): Optional task failure handler (e.g. to re-enqueue the task)

Here's a brief description of the class's methods:

• run(task: TTask): Promise<TResult> | null: Enqueues the provided task (coalescing, if applicable); if run immediately, the running task's promise (from onRunTask above) is returned (otherwise null is returned)
• stop(): void: Halts task processing (note that in-flight tasks will not be canceled/stopped)
• start(): void: Starts task processing, if it had been previously stopped
• serialize(): string: Serializes the task queue to a string
• toParsedJson(): object: Serializes the task queue to a JSON-friendly object (meaning it converts Date objects to strings that can be round-tripped through JSON.stringify() and JSON.parse())

Deserialization is done using:

• TaskManager.deserialize(json: string, options)
• TaskManager.fromParsedJson(object, options)