Node.js v25.0.0 文档
- Node.js v25.0.0
-
目录
- 异步上下文跟踪
- 介绍
- 类:
AsyncLocalStorage
new AsyncLocalStorage([options])
- 静态方法:
AsyncLocalStorage.bind(fn)
- 静态方法:
AsyncLocalStorage.snapshot()
asyncLocalStorage.disable()
asyncLocalStorage.getStore()
asyncLocalStorage.enterWith(store)
asyncLocalStorage.name
asyncLocalStorage.run(store, callback[, ...args])
asyncLocalStorage.exit(callback[, ...args])
- 与
async/await
一起使用 - 问题排查:上下文丢失
- 类:
AsyncResource
new AsyncResource(type[, options])
- 静态方法:
AsyncResource.bind(fn[, type[, thisArg]])
asyncResource.bind(fn[, thisArg])
asyncResource.runInAsyncScope(fn[, thisArg, ...args])
asyncResource.emitDestroy()
asyncResource.asyncId()
asyncResource.triggerAsyncId()
- 为
Worker
线程池使用AsyncResource
- 将
AsyncResource
与EventEmitter
集成
- 异步上下文跟踪
-
索引
- 断言测试
- 异步上下文跟踪
- 异步钩子
- 缓冲区
- C++ 插件
- 使用 Node-API 的 C/C++ 插件
- C++ 嵌入器 API
- 子进程
- 集群
- 命令行选项
- 控制台
- 加密
- 调试器
- 已弃用的 API
- 诊断通道
- DNS
- 域
- 环境变量
- 错误
- 事件
- 文件系统
- 全局对象
- HTTP
- HTTP/2
- HTTPS
- 检查器
- 国际化
- 模块:CommonJS 模块
- 模块:ECMAScript 模块
- 模块:
node:module
API - 模块:包
- 模块:TypeScript
- 网络
- 操作系统
- 路径
- 性能钩子
- 权限
- 进程
- Punycode
- 查询字符串
- 逐行读取
- REPL
- 报告
- 单一可执行文件应用
- SQLite
- 流
- 字符串解码器
- 测试运行器
- 定时器
- TLS/SSL
- 跟踪事件
- TTY
- UDP/数据报
- URL
- 实用工具
- V8
- 虚拟机
- WASI
- Web Crypto API
- Web Streams API
- 工作线程
- Zlib
- 其他版本
- 选项
异步上下文跟踪#
源代码: lib/async_hooks.js
介绍#
这些类用于关联状态并在回调函数和 Promise 链中传播。它们允许在 Web 请求或任何其他异步持续时间的生命周期内存储数据。这与其他语言中的线程局部存储(thread-local storage)类似。
AsyncLocalStorage
和 AsyncResource
类是 node:async_hooks
模块的一部分。
import { AsyncLocalStorage, AsyncResource } from 'node:async_hooks';
const { AsyncLocalStorage, AsyncResource } = require('node:async_hooks');
类:AsyncLocalStorage
#
这个类创建的存储在异步操作中保持一致。
虽然你可以在 node:async_hooks
模块之上构建自己的实现,但应优先选择 AsyncLocalStorage
,因为它是一个高性能且内存安全的实现,其中包含了许多不易实现的显著优化。
以下示例使用 AsyncLocalStorage
构建一个简单的日志记录器,它为传入的 HTTP 请求分配 ID,并将这些 ID 包含在每个请求中记录的消息里。
import http from 'node:http';
import { AsyncLocalStorage } from 'node:async_hooks';
const asyncLocalStorage = new AsyncLocalStorage();
function logWithId(msg) {
const id = asyncLocalStorage.getStore();
console.log(`${id !== undefined ? id : '-'}:`, msg);
}
let idSeq = 0;
http.createServer((req, res) => {
asyncLocalStorage.run(idSeq++, () => {
logWithId('start');
// Imagine any chain of async operations here
setImmediate(() => {
logWithId('finish');
res.end();
});
});
}).listen(8080);
http.get('https://:8080');
http.get('https://:8080');
// Prints:
// 0: start
// 0: finish
// 1: start
// 1: finish
const http = require('node:http');
const { AsyncLocalStorage } = require('node:async_hooks');
const asyncLocalStorage = new AsyncLocalStorage();
function logWithId(msg) {
const id = asyncLocalStorage.getStore();
console.log(`${id !== undefined ? id : '-'}:`, msg);
}
let idSeq = 0;
http.createServer((req, res) => {
asyncLocalStorage.run(idSeq++, () => {
logWithId('start');
// Imagine any chain of async operations here
setImmediate(() => {
logWithId('finish');
res.end();
});
});
}).listen(8080);
http.get('https://:8080');
http.get('https://:8080');
// Prints:
// 0: start
// 0: finish
// 1: start
// 1: finish
每个 AsyncLocalStorage
实例都维护一个独立的存储上下文。多个实例可以安全地同时存在,而不会有互相干扰数据的风险。
new AsyncLocalStorage([options])
#
创建一个新的 AsyncLocalStorage
实例。存储仅在 run()
调用内部或 enterWith()
调用之后提供。
静态方法:AsyncLocalStorage.bind(fn)
#
fn
<Function> 要绑定到当前执行上下文的函数。- 返回:<Function> 一个新函数,它在捕获的执行上下文中调用
fn
。
将给定的函数绑定到当前的执行上下文。
静态方法:AsyncLocalStorage.snapshot()
#
- 返回:<Function> 一个签名为
(fn: (...args) : R, ...args) : R
的新函数。
捕获当前的执行上下文并返回一个接受函数作为参数的函数。每当调用返回的函数时,它将在捕获的上下文中调用传递给它的函数。
const asyncLocalStorage = new AsyncLocalStorage();
const runInAsyncScope = asyncLocalStorage.run(123, () => AsyncLocalStorage.snapshot());
const result = asyncLocalStorage.run(321, () => runInAsyncScope(() => asyncLocalStorage.getStore()));
console.log(result); // returns 123
AsyncLocalStorage.snapshot() 可以替代 AsyncResource 用于简单的异步上下文跟踪,例如:
class Foo {
#runInAsyncScope = AsyncLocalStorage.snapshot();
get() { return this.#runInAsyncScope(() => asyncLocalStorage.getStore()); }
}
const foo = asyncLocalStorage.run(123, () => new Foo());
console.log(asyncLocalStorage.run(321, () => foo.get())); // returns 123
asyncLocalStorage.disable()
#
禁用 AsyncLocalStorage
实例。所有后续对 asyncLocalStorage.getStore()
的调用都将返回 undefined
,直到再次调用 asyncLocalStorage.run()
或 asyncLocalStorage.enterWith()
。
调用 asyncLocalStorage.disable()
时,所有与该实例关联的当前上下文都将退出。
在 asyncLocalStorage
可以被垃圾回收之前,必须调用 asyncLocalStorage.disable()
。这不适用于 asyncLocalStorage
提供的存储,因为这些对象会与相应的异步资源一起被垃圾回收。
当 asyncLocalStorage
在当前进程中不再使用时,请使用此方法。
asyncLocalStorage.getStore()
#
- 返回:<any>
返回当前存储。如果在通过调用 asyncLocalStorage.run()
或 asyncLocalStorage.enterWith()
初始化的异步上下文之外调用,则返回 undefined
。
asyncLocalStorage.enterWith(store)
#
store
<any>
在当前同步执行的剩余部分进入该上下文,然后在任何后续的异步调用中持久化该存储。
示例
const store = { id: 1 };
// Replaces previous store with the given store object
asyncLocalStorage.enterWith(store);
asyncLocalStorage.getStore(); // Returns the store object
someAsyncOperation(() => {
asyncLocalStorage.getStore(); // Returns the same object
});
这种转换将持续整个同步执行过程。这意味着,例如,如果在一个事件处理程序中进入了上下文,那么后续的事件处理程序也将在该上下文中运行,除非使用 AsyncResource
将它们明确绑定到另一个上下文。这就是为什么应该优先使用 run()
而不是 enterWith()
,除非有充分的理由使用后一种方法。
const store = { id: 1 };
emitter.on('my-event', () => {
asyncLocalStorage.enterWith(store);
});
emitter.on('my-event', () => {
asyncLocalStorage.getStore(); // Returns the same object
});
asyncLocalStorage.getStore(); // Returns undefined
emitter.emit('my-event');
asyncLocalStorage.getStore(); // Returns the same object
asyncLocalStorage.run(store, callback[, ...args])
#
store
<any>callback
<Function>...args
<any>
在一个上下文中同步运行一个函数并返回其返回值。存储在回调函数之外是不可访问的。存储对于在回调函数内创建的任何异步操作都是可访问的。
可选的 args
会被传递给回调函数。
如果回调函数抛出错误,run()
也会抛出该错误。调用堆栈不会受此调用的影响,并且上下文会被退出。
示例
const store = { id: 2 };
try {
asyncLocalStorage.run(store, () => {
asyncLocalStorage.getStore(); // Returns the store object
setTimeout(() => {
asyncLocalStorage.getStore(); // Returns the store object
}, 200);
throw new Error();
});
} catch (e) {
asyncLocalStorage.getStore(); // Returns undefined
// The error will be caught here
}
asyncLocalStorage.exit(callback[, ...args])
#
callback
<Function>...args
<any>
在一个上下文之外同步运行一个函数并返回其返回值。存储在回调函数或回调函数内创建的异步操作中是不可访问的。在回调函数内进行的任何 getStore()
调用都将始终返回 undefined
。
可选的 args
会被传递给回调函数。
如果回调函数抛出错误,exit()
也会抛出该错误。调用堆栈不会受此调用的影响,并且上下文会被重新进入。
示例
// Within a call to run
try {
asyncLocalStorage.getStore(); // Returns the store object or value
asyncLocalStorage.exit(() => {
asyncLocalStorage.getStore(); // Returns undefined
throw new Error();
});
} catch (e) {
asyncLocalStorage.getStore(); // Returns the same object or value
// The error will be caught here
}
与 async/await
一起使用#
如果在一个异步函数中,只有一个 await
调用需要在某个上下文中运行,应使用以下模式:
async function fn() {
await asyncLocalStorage.run(new Map(), () => {
asyncLocalStorage.getStore().set('key', value);
return foo(); // The return value of foo will be awaited
});
}
在这个例子中,存储仅在回调函数和被 foo
调用的函数中可用。在 run
之外调用 getStore
将返回 undefined
。
问题排查:上下文丢失#
在大多数情况下,AsyncLocalStorage
都能正常工作。在极少数情况下,当前存储会在某个异步操作中丢失。
如果你的代码是基于回调的,使用 util.promisify()
将其 Promise 化就足够了,这样它就能与原生 Promise 一起工作。
如果你需要使用基于回调的 API,或者你的代码假定了一种自定义的 thenable 实现,请使用 AsyncResource
类将异步操作与正确的执行上下文关联起来。通过在你怀疑导致上下文丢失的调用之后记录 asyncLocalStorage.getStore()
的内容,来找到导致上下文丢失的函数调用。当代码记录 undefined
时,最后被调用的那个回调函数很可能就是导致上下文丢失的原因。
类:AsyncResource
#
AsyncResource
类被设计为由嵌入者的异步资源来扩展。通过这种方式,用户可以轻松地触发他们自己资源的生命周期事件。
当一个 AsyncResource
被实例化时,init
钩子将被触发。
以下是 AsyncResource
API 的概述。
import { AsyncResource, executionAsyncId } from 'node:async_hooks';
// AsyncResource() is meant to be extended. Instantiating a
// new AsyncResource() also triggers init. If triggerAsyncId is omitted then
// async_hook.executionAsyncId() is used.
const asyncResource = new AsyncResource(
type, { triggerAsyncId: executionAsyncId(), requireManualDestroy: false },
);
// Run a function in the execution context of the resource. This will
// * establish the context of the resource
// * trigger the AsyncHooks before callbacks
// * call the provided function `fn` with the supplied arguments
// * trigger the AsyncHooks after callbacks
// * restore the original execution context
asyncResource.runInAsyncScope(fn, thisArg, ...args);
// Call AsyncHooks destroy callbacks.
asyncResource.emitDestroy();
// Return the unique ID assigned to the AsyncResource instance.
asyncResource.asyncId();
// Return the trigger ID for the AsyncResource instance.
asyncResource.triggerAsyncId();
const { AsyncResource, executionAsyncId } = require('node:async_hooks');
// AsyncResource() is meant to be extended. Instantiating a
// new AsyncResource() also triggers init. If triggerAsyncId is omitted then
// async_hook.executionAsyncId() is used.
const asyncResource = new AsyncResource(
type, { triggerAsyncId: executionAsyncId(), requireManualDestroy: false },
);
// Run a function in the execution context of the resource. This will
// * establish the context of the resource
// * trigger the AsyncHooks before callbacks
// * call the provided function `fn` with the supplied arguments
// * trigger the AsyncHooks after callbacks
// * restore the original execution context
asyncResource.runInAsyncScope(fn, thisArg, ...args);
// Call AsyncHooks destroy callbacks.
asyncResource.emitDestroy();
// Return the unique ID assigned to the AsyncResource instance.
asyncResource.asyncId();
// Return the trigger ID for the AsyncResource instance.
asyncResource.triggerAsyncId();
new AsyncResource(type[, options])
#
用法示例:
class DBQuery extends AsyncResource {
constructor(db) {
super('DBQuery');
this.db = db;
}
getInfo(query, callback) {
this.db.get(query, (err, data) => {
this.runInAsyncScope(callback, null, err, data);
});
}
close() {
this.db = null;
this.emitDestroy();
}
}
静态方法:AsyncResource.bind(fn[, type[, thisArg]])
#
fn
<Function> 要绑定到当前执行上下文的函数。type
<string> 一个可选的名称,用于关联底层的AsyncResource
。thisArg
<any>
将给定的函数绑定到当前的执行上下文。
asyncResource.bind(fn[, thisArg])
#
fn
<Function> 要绑定到当前AsyncResource
的函数。thisArg
<any>
将给定的函数绑定到此 AsyncResource
的作用域中执行。
asyncResource.runInAsyncScope(fn[, thisArg, ...args])
#
fn
<Function> 在此异步资源的执行上下文中调用的函数。thisArg
<any> 用于函数调用的接收者。...args
<any> 传递给函数的可选参数。
在异步资源的执行上下文中,使用提供的参数调用提供的函数。这将建立上下文,触发 AsyncHooks 的 before 回调,调用函数,触发 AsyncHooks 的 after 回调,然后恢复原始的执行上下文。
asyncResource.emitDestroy()
#
- 返回:<AsyncResource> 对
asyncResource
的引用。
调用所有 destroy
钩子。这应该只被调用一次。如果调用超过一次,将会抛出错误。这**必须**被手动调用。如果资源被留给垃圾回收器(GC)收集,那么 destroy
钩子将永远不会被调用。
为 Worker
线程池使用 AsyncResource
#
以下示例展示了如何使用 AsyncResource
类为 Worker
池正确地提供异步跟踪。其他资源池,如数据库连接池,可以遵循类似的模型。
假设任务是计算两个数字的和,使用一个名为 task_processor.js
的文件,内容如下:
import { parentPort } from 'node:worker_threads';
parentPort.on('message', (task) => {
parentPort.postMessage(task.a + task.b);
});
const { parentPort } = require('node:worker_threads');
parentPort.on('message', (task) => {
parentPort.postMessage(task.a + task.b);
});
围绕它构建的 Worker 池可以使用以下结构:
import { AsyncResource } from 'node:async_hooks';
import { EventEmitter } from 'node:events';
import { Worker } from 'node:worker_threads';
const kTaskInfo = Symbol('kTaskInfo');
const kWorkerFreedEvent = Symbol('kWorkerFreedEvent');
class WorkerPoolTaskInfo extends AsyncResource {
constructor(callback) {
super('WorkerPoolTaskInfo');
this.callback = callback;
}
done(err, result) {
this.runInAsyncScope(this.callback, null, err, result);
this.emitDestroy(); // `TaskInfo`s are used only once.
}
}
export default class WorkerPool extends EventEmitter {
constructor(numThreads) {
super();
this.numThreads = numThreads;
this.workers = [];
this.freeWorkers = [];
this.tasks = [];
for (let i = 0; i < numThreads; i++)
this.addNewWorker();
// Any time the kWorkerFreedEvent is emitted, dispatch
// the next task pending in the queue, if any.
this.on(kWorkerFreedEvent, () => {
if (this.tasks.length > 0) {
const { task, callback } = this.tasks.shift();
this.runTask(task, callback);
}
});
}
addNewWorker() {
const worker = new Worker(new URL('task_processor.js', import.meta.url));
worker.on('message', (result) => {
// In case of success: Call the callback that was passed to `runTask`,
// remove the `TaskInfo` associated with the Worker, and mark it as free
// again.
worker[kTaskInfo].done(null, result);
worker[kTaskInfo] = null;
this.freeWorkers.push(worker);
this.emit(kWorkerFreedEvent);
});
worker.on('error', (err) => {
// In case of an uncaught exception: Call the callback that was passed to
// `runTask` with the error.
if (worker[kTaskInfo])
worker[kTaskInfo].done(err, null);
else
this.emit('error', err);
// Remove the worker from the list and start a new Worker to replace the
// current one.
this.workers.splice(this.workers.indexOf(worker), 1);
this.addNewWorker();
});
this.workers.push(worker);
this.freeWorkers.push(worker);
this.emit(kWorkerFreedEvent);
}
runTask(task, callback) {
if (this.freeWorkers.length === 0) {
// No free threads, wait until a worker thread becomes free.
this.tasks.push({ task, callback });
return;
}
const worker = this.freeWorkers.pop();
worker[kTaskInfo] = new WorkerPoolTaskInfo(callback);
worker.postMessage(task);
}
close() {
for (const worker of this.workers) worker.terminate();
}
}
const { AsyncResource } = require('node:async_hooks');
const { EventEmitter } = require('node:events');
const path = require('node:path');
const { Worker } = require('node:worker_threads');
const kTaskInfo = Symbol('kTaskInfo');
const kWorkerFreedEvent = Symbol('kWorkerFreedEvent');
class WorkerPoolTaskInfo extends AsyncResource {
constructor(callback) {
super('WorkerPoolTaskInfo');
this.callback = callback;
}
done(err, result) {
this.runInAsyncScope(this.callback, null, err, result);
this.emitDestroy(); // `TaskInfo`s are used only once.
}
}
class WorkerPool extends EventEmitter {
constructor(numThreads) {
super();
this.numThreads = numThreads;
this.workers = [];
this.freeWorkers = [];
this.tasks = [];
for (let i = 0; i < numThreads; i++)
this.addNewWorker();
// Any time the kWorkerFreedEvent is emitted, dispatch
// the next task pending in the queue, if any.
this.on(kWorkerFreedEvent, () => {
if (this.tasks.length > 0) {
const { task, callback } = this.tasks.shift();
this.runTask(task, callback);
}
});
}
addNewWorker() {
const worker = new Worker(path.resolve(__dirname, 'task_processor.js'));
worker.on('message', (result) => {
// In case of success: Call the callback that was passed to `runTask`,
// remove the `TaskInfo` associated with the Worker, and mark it as free
// again.
worker[kTaskInfo].done(null, result);
worker[kTaskInfo] = null;
this.freeWorkers.push(worker);
this.emit(kWorkerFreedEvent);
});
worker.on('error', (err) => {
// In case of an uncaught exception: Call the callback that was passed to
// `runTask` with the error.
if (worker[kTaskInfo])
worker[kTaskInfo].done(err, null);
else
this.emit('error', err);
// Remove the worker from the list and start a new Worker to replace the
// current one.
this.workers.splice(this.workers.indexOf(worker), 1);
this.addNewWorker();
});
this.workers.push(worker);
this.freeWorkers.push(worker);
this.emit(kWorkerFreedEvent);
}
runTask(task, callback) {
if (this.freeWorkers.length === 0) {
// No free threads, wait until a worker thread becomes free.
this.tasks.push({ task, callback });
return;
}
const worker = this.freeWorkers.pop();
worker[kTaskInfo] = new WorkerPoolTaskInfo(callback);
worker.postMessage(task);
}
close() {
for (const worker of this.workers) worker.terminate();
}
}
module.exports = WorkerPool;
如果没有 WorkerPoolTaskInfo
对象添加的显式跟踪,回调似乎会与单个 Worker
对象相关联。然而,Worker
的创建与任务的创建无关,并且不提供任务何时被调度的信息。
这个池可以按如下方式使用:
import WorkerPool from './worker_pool.js';
import os from 'node:os';
const pool = new WorkerPool(os.availableParallelism());
let finished = 0;
for (let i = 0; i < 10; i++) {
pool.runTask({ a: 42, b: 100 }, (err, result) => {
console.log(i, err, result);
if (++finished === 10)
pool.close();
});
}
const WorkerPool = require('./worker_pool.js');
const os = require('node:os');
const pool = new WorkerPool(os.availableParallelism());
let finished = 0;
for (let i = 0; i < 10; i++) {
pool.runTask({ a: 42, b: 100 }, (err, result) => {
console.log(i, err, result);
if (++finished === 10)
pool.close();
});
}
将 AsyncResource
与 EventEmitter
集成#
由 EventEmitter
触发的事件监听器可能在与调用 eventEmitter.on()
时活跃的执行上下文不同的上下文中运行。
以下示例展示了如何使用 AsyncResource
类将事件监听器与正确的执行上下文正确关联。同样的方法可以应用于 Stream
或类似的事件驱动类。
import { createServer } from 'node:http';
import { AsyncResource, executionAsyncId } from 'node:async_hooks';
const server = createServer((req, res) => {
req.on('close', AsyncResource.bind(() => {
// Execution context is bound to the current outer scope.
}));
req.on('close', () => {
// Execution context is bound to the scope that caused 'close' to emit.
});
res.end();
}).listen(3000);
const { createServer } = require('node:http');
const { AsyncResource, executionAsyncId } = require('node:async_hooks');
const server = createServer((req, res) => {
req.on('close', AsyncResource.bind(() => {
// Execution context is bound to the current outer scope.
}));
req.on('close', () => {
// Execution context is bound to the scope that caused 'close' to emit.
});
res.end();
}).listen(3000);