prex-es5/out/lib/queue.js

Async coordination primitives and extensions on top of ES6 Promises

/*! *****************************************************************************
Copyright (c) Microsoft Corporation.
Licensed under the Apache License, Version 2.0.

See LICENSE file in the project root for details.
***************************************************************************** */
import { isMissing, isIterable } from "./utils";
/**
 * An asynchronous queue.
 */
export class AsyncQueue {
    /**
     * Initializes a new instance of the AsyncQueue class.
     *
     * @param iterable An optional iterable of values or promises.
     */
    constructor(iterable) {
        this._available = undefined;
        this._pending = undefined;
        if (!isIterable(iterable, /*optional*/ true))
            throw new TypeError("Object not iterable: iterable.");
        if (!isMissing(iterable)) {
            this._available = [];
            for (const value of iterable) {
                this._available.push(Promise.resolve(value));
            }
        }
    }
    /**
     * Gets the number of entries in the queue.
     * When positive, indicates the number of entries available to get.
     * When negative, indicates the number of requests waiting to be fulfilled.
     */
    get size() {
        if (this._available && this._available.length > 0) {
            return this._available.length;
        }
        if (this._pending && this._pending.length > 0) {
            return -this._pending.length;
        }
        return 0;
    }
    /**
     * Adds a value to the end of the queue. If the queue is empty but has a pending
     * dequeue request, the value will be dequeued and the request fulfilled.
     *
     * @param value A value or promise to add to the queue.
     */
    put(value) {
        if (this._pending !== undefined) {
            const resolve = this._pending.shift();
            if (resolve !== undefined) {
                resolve(value);
                return;
            }
        }
        if (this._available === undefined) {
            this._available = [];
        }
        this._available.push(Promise.resolve(value));
    }
    /**
     * Removes and returns a Promise for the first value in the queue. If the queue is empty,
     * returns a Promise for the next value to be added to the queue.
     */
    get() {
        if (this._available !== undefined) {
            const promise = this._available.shift();
            if (promise !== undefined) {
                return promise;
            }
        }
        if (this._pending === undefined) {
            this._pending = [];
        }
        return new Promise(resolve => { this._pending.push(resolve); });
    }
}

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