FifoOperationQueueCache.js

FifoOperationQueueCache.js

// @ts-nocheck
function createDeferredPromise(){
    let res, rej
    const promise = new Promise((resolve, reject) => { [res, rej] = [resolve, reject] })
    promise.resolve = res
    promise.reject = rej
    return promise
}

class FifoOperationQueue {
    constructor({ onEmpty }){
        this.onEmpty = onEmpty || function(){}
        this.idGen = 0
        this.queue = []
        this.promises = {}
        this.state = 'idle'
    }
    generateId(){
        return this.idGen++
    }
    push(operation, input){
        // Init queue array
        const itemId = this.generateId()
        this.queue.push({
            operation,
            input,
            id: itemId
        })
        // Create promise
        const dPromise = this.promises[itemId] = createDeferredPromise()

        // Run the queue (don't await)
        this.runQueue()

        // Return dPromise so client can await on it's completion if it needs
        return dPromise
    }
    async runQueue(){
        // Already running, skip.
        if(this.state == 'running'){ return }

        // Set status to running
        this.state = 'running'

        // Execute operations (FIFO) until queue is empty
        while(this.queue.length){
            // Pull the first item from the queue
            const item = this.queue.shift()
            const promise = this.promises[item.id]
            delete this.promises[item.id]
            try {
                promise.resolve(
                    await item.operation(item.input)
                )
            }
            catch(e){ promise.reject(e) }
        }

        // Emit on empty
        this.onEmpty()

        // Set status for this queue to idle
        this.state = 'idle'
    }
}

export default class FifoOperationQueueCache {
    constructor(){
        this.queues = {}
    }
    push(queueId, operation, input){
        // Init queue array
        if(!this.queues[queueId]){
            const self = this
            this.queues[queueId] = new FifoOperationQueue({
                onEmpty(){ delete self.queues[queueId] }
            })
        }
        // Returns a promise
        return this.queues[queueId].push(operation, input)
    }
}