Asynchronous Bounded Queue

asyncqueue-no-debug.ts

class AsyncQueue<T> {
    waitingEnqueue = new Array<() => void>()
    waitingDequeue = new Array<() => void>()
    enqueuePointer = 0
    dequeuePointer = 0
    queue = Array<T>()
    maxSize = 1

    async enqueue(x: T) {
        if ((this.queue.length + 1) > this.maxSize || this.waitingDequeue.length > 0) {
            this.dequeuePointer += 1
            await new Promise(r => this.waitingDequeue.unshift(r))
            this.waitingDequeue.pop()
        }

        this.queue.unshift(x)

        if (this.enqueuePointer > 0) {
            this.waitingEnqueue[this.enqueuePointer-1]()
            this.enqueuePointer -= 1
        }
    }

    async dequeue() {
        if (this.queue.length == 0 || this.waitingEnqueue.length > 0) {
            this.enqueuePointer += 1
            await new Promise(r => this.waitingEnqueue.unshift(r))
            this.waitingEnqueue.pop()
        }

        if (this.dequeuePointer > 0) {
            this.waitingDequeue[this.dequeuePointer - 1]()
            this.dequeuePointer -= 1
        }

        return this.queue.pop()!
    }
}

asyncqueue-semaphore.ts

class AsyncSemaphore {
    private promises = Array<() => void>()

    constructor(private i: number) {}

    signal() {
        if (this.promises.length > 0) this.promises.pop()()
        this.i += 1
    }

    async wait() {
        if (this.i == 0 || this.promises.length > 0)
            await new Promise(r => this.promises.unshift(r))
        this.i -= 1
    }
}

class AsyncQueue<T> {
    private queue = Array<T>()
    private waitingEnqueue: AsyncSemaphore
    private waitingDequeue: AsyncSemaphore

    constructor(readonly maxSize: number) {
        this.waitingEnqueue = new AsyncSemaphore(0)
        this.waitingDequeue = new AsyncSemaphore(maxSize)
    }

    async enqueue(x: T) {
        await this.waitingDequeue.wait()
        this.queue.unshift(x)
        this.waitingEnqueue.signal()
    }

    async dequeue() {
        await this.waitingEnqueue.wait()
        this.waitingDequeue.signal()
        return this.queue.pop()!
    }
}

asyncqueue.ts

class AsyncQueue<T> {
    waitingEnqueue = new Array<() => void>()
    waitingDequeue = new Array<() => void>()
    enqueuePointer = 0
    dequeuePointer = 0
    queue = Array<T>()
    maxSize = 1
    trace = 0

    async enqueue(x: T) {
        this.trace += 1
        const localTrace = this.trace

        if ((this.queue.length + 1) > this.maxSize || this.waitingDequeue.length > 0) {
            console.debug(`[${localTrace}] Producer Waiting`)
            this.dequeuePointer += 1
            await new Promise(r => this.waitingDequeue.unshift(r))
            this.waitingDequeue.pop()
            console.debug(`[${localTrace}] Producer Ready`)
        }

        this.queue.unshift(x)
        console.debug(`[${localTrace}] Enqueueing ${x} Queue is now [${this.queue.join(', ')}]`)

        if (this.enqueuePointer > 0) {
            console.debug(`[${localTrace}] Notify Consumer`)
            this.waitingEnqueue[this.enqueuePointer-1]()
            this.enqueuePointer -= 1
        }
    }

    async dequeue() {
        this.trace += 1
        const localTrace = this.trace

        console.debug(`[${localTrace}] Queue length before pop: ${this.queue.length}`)

        if (this.queue.length == 0 || this.waitingEnqueue.length > 0) {
            console.debug(`[${localTrace}] Consumer Waiting`)
            this.enqueuePointer += 1
            await new Promise(r => this.waitingEnqueue.unshift(r))
            this.waitingEnqueue.pop()
            console.debug(`[${localTrace}] Consumer Ready`)
        }

        const x = this.queue.pop()!
        console.debug(`[${localTrace}] Queue length after pop: ${this.queue.length} Popping ${x}`)

        if (this.dequeuePointer > 0) {
            console.debug(`[${localTrace}] Notify Producer`)
            this.waitingDequeue[this.dequeuePointer - 1]()
            this.dequeuePointer -= 1
        }

        return x
    }
}

test.ts

async function produce<T>(q: AsyncQueue<T>, x: T) {
    await q.enqueue(x)
}

async function consume<T>(q: AsyncQueue<T>) {
    return await q.dequeue()
}

(async () => {
    const q = new AsyncQueue<number>()
    consume(q).then(console.log)
    consume(q).then(console.log)
    produce(q, 3)
    produce(q, 4)
    consume(q).then(console.log)
    consume(q).then(console.log)
    produce(q, 5)
    produce(q, 6)
    produce(q, 7)
    produce(q, 8)
    consume(q).then(console.log)
    consume(q).then(console.log)
})()