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1/*2 * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.3 * SPDX-License-Identifier: Apache-2.0.4 */5 6/**7 * Module for base types related to event emission8 *9 * @packageDocumentation10 * @module event11 */12 13import { EventEmitter } from 'events';14 15/**16 * Events are named via string or symbol17 *18 * @category Events19 */20export type EventKey = string | symbol;21 22export type EventEmissionCallback = () => void23 24/**25 * @internal26 */27class BufferedEvent {28    public callback?: EventEmissionCallback;29    public next?: BufferedEvent;30    public args: any[];31    constructor(public event: EventKey, args: any[]) {32        this.args = args;33    }34 35    static newWithEmissionCallback(key: EventKey, callback: EventEmissionCallback, args: any[]) : BufferedEvent {36        let bufferedEvent : BufferedEvent = new BufferedEvent(key, args);37        bufferedEvent.callback = callback;38 39        return bufferedEvent;40    }41}42 43/**44 * Provides buffered event emitting semantics, similar to many Node-style streams.45 * Subclasses will override EventEmitter.on() and trigger uncorking.46 * NOTE: It is HIGHLY recommended that uncorking should always be done via47 * ```process.nextTick()```, not during the EventEmitter.on() call.48 *49 * See also: [Node writable streams](https://nodejs.org/api/stream.html#stream_writable_cork)50 *51 * @category Events52 */53export class BufferedEventEmitter extends EventEmitter {54    private corked = false;55    private eventQueue?: BufferedEvent;56    private lastQueuedEvent?: BufferedEvent;57 58    constructor() {59        super();60    }61 62    /**63     * Forces all written events to be buffered in memory. The buffered data will be64     * flushed when {@link BufferedEventEmitter.uncork} is called.65     */66    cork() {67        this.corked = true;68    }69 70    /**71     * Flushes all data buffered since {@link BufferedEventEmitter.cork} was called.72     *73     * NOTE: It is HIGHLY recommended that uncorking should always be done via74     * ``` process.nextTick```, not during the ```EventEmitter.on()``` call.75     */76    uncork() {77        this.corked = false;78        while (this.eventQueue) {79            const event = this.eventQueue;80            super.emit(event.event, ...event.args);81            if (event.callback) {82                event.callback();83            }84            this.eventQueue = this.eventQueue.next;85        }86    }87 88    /**89     * Synchronously calls each of the listeners registered for the event key supplied90     * in registration order. If the {@link BufferedEventEmitter} is currently corked,91     * the event will be buffered until {@link BufferedEventEmitter.uncork} is called.92     * @param event The name of the event93     * @param args Event payload94     */95    emit(event: EventKey, ...args: any[]): boolean {96        if (this.corked) {97            // queue requests in order98            let last = this.lastQueuedEvent;99            this.lastQueuedEvent = new BufferedEvent(event, args);100            if (last) {101                last.next = this.lastQueuedEvent;102            } else {103                this.eventQueue = this.lastQueuedEvent;104            }105            return this.listeners(event).length > 0;106        }107 108        return super.emit(event, ...args);109    }110 111    emitWithCallback(event: EventKey, emissionCallback: EventEmissionCallback, ...args: any[]) : boolean {112        if (this.corked) {113            // queue requests in order114            let last = this.lastQueuedEvent;115            this.lastQueuedEvent = BufferedEvent.newWithEmissionCallback(event, emissionCallback, args);116            if (last) {117                last.next = this.lastQueuedEvent;118            } else {119                this.eventQueue = this.lastQueuedEvent;120            }121            return this.listeners(event).length > 0;122        }123 124        let result = super.emit(event, ...args);125        emissionCallback();126        return result;127    }128}129