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AsyncQueue.js
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Wed, Feb 19, 20:07

AsyncQueue.js
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/*
MIT License http://www.opensource.org/licenses/mit-license.php
Author Tobias Koppers @sokra
*/
"use strict";
const { SyncHook, AsyncSeriesHook } = require("tapable");
const QUEUED_STATE = 0;
const PROCESSING_STATE = 1;
const DONE_STATE = 2;
let inHandleResult = 0;
/**
* @template T
* @callback Callback
* @param {Error=} err
* @param {T=} result
*/
/**
* @template T
* @template K
* @template R
*/
class AsyncQueueEntry {
/**
* @param {T} item the item
* @param {Callback<R>} callback the callback
*/
constructor(item, callback) {
this.item = item;
/** @type {typeof QUEUED_STATE | typeof PROCESSING_STATE | typeof DONE_STATE} */
this.state = QUEUED_STATE;
this.callback = callback;
/** @type {Callback<R>[] | undefined} */
this.callbacks = undefined;
this.result = undefined;
this.error = undefined;
}
}
/**
* @template T
* @template K
* @template R
*/
class AsyncQueue {
/**
* @param {Object} options options object
* @param {string=} options.name name of the queue
* @param {number} options.parallelism how many items should be processed at once
* @param {function(T): K=} options.getKey extract key from item
* @param {function(T, Callback<R>): void} options.processor async function to process items
*/
constructor({ name, parallelism, processor, getKey }) {
this._name = name;
this._parallelism = parallelism;
this._processor = processor;
this._getKey =
getKey || /** @type {(T) => K} */ (item => /** @type {any} */ (item));
/** @type {Map<K, AsyncQueueEntry<T, K, R>>} */
this._entries = new Map();
/** @type {AsyncQueueEntry<T, K, R>[]} */
this._queued = [];
this._activeTasks = 0;
this._willEnsureProcessing = false;
this._stopped = false;
this.hooks = {
/** @type {AsyncSeriesHook<[T]>} */
beforeAdd: new AsyncSeriesHook(["item"]),
/** @type {SyncHook<[T]>} */
added: new SyncHook(["item"]),
/** @type {AsyncSeriesHook<[T]>} */
beforeStart: new AsyncSeriesHook(["item"]),
/** @type {SyncHook<[T]>} */
started: new SyncHook(["item"]),
/** @type {SyncHook<[T, Error, R]>} */
result: new SyncHook(["item", "error", "result"])
};
this._ensureProcessing = this._ensureProcessing.bind(this);
}
/**
* @param {T} item a item
* @param {Callback<R>} callback callback function
* @returns {void}
*/
add(item, callback) {
if (this._stopped) return callback(new Error("Queue was stopped"));
this.hooks.beforeAdd.callAsync(item, err => {
if (err) {
callback(err);
return;
}
const key = this._getKey(item);
const entry = this._entries.get(key);
if (entry !== undefined) {
if (entry.state === DONE_STATE) {
process.nextTick(() => callback(entry.error, entry.result));
} else if (entry.callbacks === undefined) {
entry.callbacks = [callback];
} else {
entry.callbacks.push(callback);
}
return;
}
const newEntry = new AsyncQueueEntry(item, callback);
if (this._stopped) {
this.hooks.added.call(item);
this._activeTasks++;
process.nextTick(() =>
this._handleResult(newEntry, new Error("Queue was stopped"))
);
} else {
this._entries.set(key, newEntry);
this._queued.push(newEntry);
if (this._willEnsureProcessing === false) {
this._willEnsureProcessing = true;
setImmediate(this._ensureProcessing);
}
this.hooks.added.call(item);
}
});
}
/**
* @param {T} item a item
* @returns {void}
*/
invalidate(item) {
const key = this._getKey(item);
const entry = this._entries.get(key);
this._entries.delete(key);
if (entry.state === QUEUED_STATE) {
const idx = this._queued.indexOf(entry);
if (idx >= 0) {
this._queued.splice(idx, 1);
}
}
}
/**
* @returns {void}
*/
stop() {
this._stopped = true;
const queue = this._queued;
this._queued = [];
for (const entry of queue) {
this._entries.delete(this._getKey(entry.item));
this._activeTasks++;
this._handleResult(entry, new Error("Queue was stopped"));
}
}
/**
* @returns {void}
*/
increaseParallelism() {
this._parallelism++;
/* istanbul ignore next */
if (this._willEnsureProcessing === false && this._queued.length > 0) {
this._willEnsureProcessing = true;
setImmediate(this._ensureProcessing);
}
}
/**
* @returns {void}
*/
decreaseParallelism() {
this._parallelism--;
}
/**
* @param {T} item an item
* @returns {boolean} true, if the item is currently being processed
*/
isProcessing(item) {
const key = this._getKey(item);
const entry = this._entries.get(key);
return entry !== undefined && entry.state === PROCESSING_STATE;
}
/**
* @param {T} item an item
* @returns {boolean} true, if the item is currently queued
*/
isQueued(item) {
const key = this._getKey(item);
const entry = this._entries.get(key);
return entry !== undefined && entry.state === QUEUED_STATE;
}
/**
* @param {T} item an item
* @returns {boolean} true, if the item is currently queued
*/
isDone(item) {
const key = this._getKey(item);
const entry = this._entries.get(key);
return entry !== undefined && entry.state === DONE_STATE;
}
/**
* @returns {void}
*/
_ensureProcessing() {
while (this._activeTasks < this._parallelism && this._queued.length > 0) {
const entry = this._queued.pop();
this._activeTasks++;
entry.state = PROCESSING_STATE;
this._startProcessing(entry);
}
this._willEnsureProcessing = false;
}
/**
* @param {AsyncQueueEntry<T, K, R>} entry the entry
* @returns {void}
*/
_startProcessing(entry) {
this.hooks.beforeStart.callAsync(entry.item, err => {
if (err) {
this._handleResult(entry, err);
return;
}
let inCallback = false;
try {
this._processor(entry.item, (e, r) => {
inCallback = true;
this._handleResult(entry, e, r);
});
} catch (err) {
if (inCallback) throw err;
this._handleResult(entry, err, null);
}
this.hooks.started.call(entry.item);
});
}
/**
* @param {AsyncQueueEntry<T, K, R>} entry the entry
* @param {Error=} err error, if any
* @param {R=} result result, if any
* @returns {void}
*/
_handleResult(entry, err, result) {
this.hooks.result.callAsync(entry.item, err, result, hookError => {
const error = hookError || err;
const callback = entry.callback;
const callbacks = entry.callbacks;
entry.state = DONE_STATE;
entry.callback = undefined;
entry.callbacks = undefined;
entry.result = result;
entry.error = error;
this._activeTasks--;
if (this._willEnsureProcessing === false && this._queued.length > 0) {
this._willEnsureProcessing = true;
setImmediate(this._ensureProcessing);
}
if (inHandleResult++ > 3) {
process.nextTick(() => {
callback(error, result);
if (callbacks !== undefined) {
for (const callback of callbacks) {
callback(error, result);
}
}
});
} else {
callback(error, result);
if (callbacks !== undefined) {
for (const callback of callbacks) {
callback(error, result);
}
}
}
inHandleResult--;
});
}
}
module.exports = AsyncQueue;

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