event-emitters/dist.es2018/Queue.js

event emitters

const INITIAL_CAPACITY = 16;
/**
 * An efficient queue implemented with a circular buffer. It implements just enough
 * interface to be useful to EventEmitterAsyncIterator.
 */
export class Queue {
    constructor(capacity = INITIAL_CAPACITY) {
        this.headIndex = 0;
        this.tailIndex = -1;
        // writing to this would corrupt the Queue but disallowing it would incur a performance hit
        this.length = 0;
        this.buffer = new Array(capacity);
    }
    enqueue(item) {
        if (this.length === this.buffer.length) {
            const prevCapacity = this.buffer.length;
            this.buffer.length *= 2;
            if (this.headIndex / prevCapacity <= 0.5) {
                if (this.headIndex !== 0) {
                    // move elements before head after tail
                    for (let i = 0; i < this.headIndex; ++i) {
                        this.buffer[prevCapacity + i] = this.buffer[i];
                        delete this.buffer[i];
                    }
                    this.tailIndex += prevCapacity;
                }
            }
            else {
                for (let i = this.tailIndex + 1; i < prevCapacity; ++i) {
                    this.buffer[prevCapacity + i] = this.buffer[i];
                    delete this.buffer[i];
                }
                this.headIndex += prevCapacity;
            }
        }
        this.tailIndex = (this.tailIndex + 1) % this.buffer.length;
        this.buffer[this.tailIndex] = item;
        ++this.length;
    }
    dequeue() {
        if (this.length === 0) {
            throw new Error('Cannot dequeue from empty Queue');
        }
        --this.length;
        // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
        const item = this.buffer[this.headIndex];
        delete this.buffer[this.headIndex];
        this.headIndex = (this.headIndex + 1) % this.buffer.length;
        return item;
    }
    // clear the buffer and leave a corrupt useless buggy object remaining
    destroy() {
        this.buffer.length = 0;
    }
}
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