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doc/api
- async_context.md
lib
- async_hooks.js
test/async-hooks
- test-async-local-storage-stop-propagation.js

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`‎doc/api/async_context.md‎`

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+20-1Lines changed: 20 additions & 1 deletion

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Original file line number	Diff line number	Diff line change
@@ -116,17 +116,35 @@ Each instance of `AsyncLocalStorage` maintains an independent storage context.
`116`	`116`	`Multiple instances can safely exist simultaneously without risk of interfering`
`117`	`117`	`with each other's data.`
`118`	`118`
`119`		-### `new AsyncLocalStorage()`
	`119`	+### `new AsyncLocalStorage([options])`
`120`	`120`
`121`	`121`	`<!-- YAML`
`122`	`122`	`added:`
`123`	`123`	`- v13.10.0`
`124`	`124`	`- v12.17.0`
	`125`	`+changes:`
	`126`	`+ - version: REPLACEME`
	`127`	`+ pr-url: https://github.com/nodejs/node/pull/45386`
	`128`	`+ description: Add option onPropagate.`
`125`	`129`	`-->`
`126`	`130`
	`131`	+> Stability: 1 - `options.onPropagate` is experimental.
	`132`	`+`
	`133`	+* `options` {Object}
	`134`	+ * `onPropagate` {Function} Optional callback invoked before a store is
	`135`	+ propagated to a new async resource. Returning `true` allows propagation,
	`136`	+ returning `false` avoids it. Default is to propagate always.
	`137`	`+`
`127`	`138`	Creates a new instance of `AsyncLocalStorage`. Store is only provided within a
`128`	`139`	`run()` call or after an `enterWith()` call.
`129`	`140`
	`141`	+The `onPropagate` is called during creation of an async resource. Throwing at
	`142`	`+this time will print the stack trace and exit. See`
	`143`	+[`async_hooks` Error handling][] for details.
	`144`	`+`
	`145`	+Creating an async resource within the `onPropagate` callback will result in
	`146`	+a recursive call to `onPropagate`.
	`147`	`+`
`130`	`148`	### `asyncLocalStorage.disable()`
`131`	`149`
`132`	`150`	`<!-- YAML`
`@@ -816,4 +834,5 @@ const server = createServer((req, res) => {`
`816`	`834`	[`EventEmitter`]: events.md#class-eventemitter
`817`	`835`	[`Stream`]: stream.md#stream
`818`	`836`	[`Worker`]: worker_threads.md#class-worker
	`837`	+[`async_hooks` Error handling]: async_hooks.md#error-handling
`819`	`838`	[`util.promisify()`]: util.md#utilpromisifyoriginal

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`‎lib/async_hooks.js‎`

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+19-4Lines changed: 19 additions & 4 deletions

Original file line number	Diff line number	Diff line change
`@@ -18,6 +18,7 @@ const {`
`18`	`18`	`const {`
`19`	`19`	`ERR_ASYNC_CALLBACK,`
`20`	`20`	`ERR_ASYNC_TYPE,`
	`21`	`+ ERR_INVALID_ARG_TYPE,`
`21`	`22`	`ERR_INVALID_ASYNC_ID`
`22`	`23`	`} = require('internal/errors').codes;`
`23`	`24`	`const { kEmptyObject } = require('internal/util');`
`@@ -268,15 +269,27 @@ const storageHook = createHook({`
`268`	`269`	`const currentResource = executionAsyncResource();`
`269`	`270`	`// Value of currentResource is always a non null object`
`270`	`271`	`for (let i = 0; i < storageList.length; ++i) {`
`271`		`- storageList[i]._propagate(resource, currentResource);`
	`272`	`+ storageList[i]._propagate(resource, currentResource, type);`
`272`	`273`	`}`
`273`	`274`	`}`
`274`	`275`	`});`
`275`	`276`
`276`	`277`	`class AsyncLocalStorage {`
`277`		`- constructor() {`
	`278`	`+ constructor(options = kEmptyObject) {`
	`279`	`+ if (typeof options !== 'object' \|\| options === null) {`
	`280`	`+ throw new ERR_INVALID_ARG_TYPE('options', 'Object', options);`
	`281`	`+ }`
	`282`	`+`
	`283`	`+ const { onPropagate = null } = options;`
	`284`	`+ if (onPropagate !== null && typeof onPropagate !== 'function') {`
	`285`	`+ throw new ERR_INVALID_ARG_TYPE('options.onPropagate',`
	`286`	`+ 'function',`
	`287`	`+ onPropagate);`
	`288`	`+ }`
	`289`	`+`
`278`	`290`	`this.kResourceStore = Symbol('kResourceStore');`
`279`	`291`	`this.enabled = false;`
	`292`	`+ this._onPropagate = onPropagate;`
`280`	`293`	`}`
`281`	`294`
`282`	`295`	`disable() {`
`@@ -300,10 +313,12 @@ class AsyncLocalStorage {`
`300`	`313`	`}`
`301`	`314`
`302`	`315`	`// Propagate the context from a parent resource to a child one`
`303`		`- _propagate(resource, triggerResource) {`
	`316`	`+ _propagate(resource, triggerResource, type) {`
`304`	`317`	`const store = triggerResource[this.kResourceStore];`
`305`	`318`	`if (this.enabled) {`
`306`		`- resource[this.kResourceStore] = store;`
	`319`	`+ if (this._onPropagate === null \|\| this._onPropagate(type, store)) {`
	`320`	`+ resource[this.kResourceStore] = store;`
	`321`	`+ }`
`307`	`322`	`}`
`308`	`323`	`}`
`309`	`324`

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`‎test/async-hooks/test-async-local-storage-stop-propagation.js‎`

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+50Lines changed: 50 additions & 0 deletions

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,50 @@`
	`1`	`+'use strict';`
	`2`	`+const common = require('../common');`
	`3`	`+const assert = require('assert');`
	`4`	`+const { AsyncLocalStorage, AsyncResource } = require('async_hooks');`
	`5`	`+`
	`6`	`+let cnt = 0;`
	`7`	`+function onPropagate(type, store) {`
	`8`	`+ assert.strictEqual(als.getStore(), store);`
	`9`	`+ cnt++;`
	`10`	`+ if (cnt === 1) {`
	`11`	`+ assert.strictEqual(type, 'r1');`
	`12`	`+ return true;`
	`13`	`+ }`
	`14`	`+ if (cnt === 2) {`
	`15`	`+ assert.strictEqual(type, 'r2');`
	`16`	`+ return false;`
	`17`	`+ }`
	`18`	`+}`
	`19`	`+`
	`20`	`+const als = new AsyncLocalStorage({`
	`21`	`+ onPropagate: common.mustCall(onPropagate, 2)`
	`22`	`+});`
	`23`	`+`
	`24`	`+const myStore = {};`
	`25`	`+`
	`26`	`+als.run(myStore, common.mustCall(() => {`
	`27`	`+ const r1 = new AsyncResource('r1');`
	`28`	`+ const r2 = new AsyncResource('r2');`
	`29`	`+ r1.runInAsyncScope(common.mustCall(() => {`
	`30`	`+ assert.strictEqual(als.getStore(), myStore);`
	`31`	`+ }));`
	`32`	`+ r2.runInAsyncScope(common.mustCall(() => {`
	`33`	`+ assert.strictEqual(als.getStore(), undefined);`
	`34`	`+ r1.runInAsyncScope(common.mustCall(() => {`
	`35`	`+ assert.strictEqual(als.getStore(), myStore);`
	`36`	`+ }));`
	`37`	`+ }));`
	`38`	`+}));`
	`39`	`+`
	`40`	`+assert.throws(() => new AsyncLocalStorage(15), {`
	`41`	`+ message: 'The "options" argument must be of type object. Received type number (15)',`
	`42`	`+ code: 'ERR_INVALID_ARG_TYPE',`
	`43`	`+ name: 'TypeError'`
	`44`	`+});`
	`45`	`+`
	`46`	`+assert.throws(() => new AsyncLocalStorage({ onPropagate: 'bar' }), {`
	`47`	`+ message: 'The "options.onPropagate" property must be of type function. Received type string (\'bar\')',`
	`48`	`+ code: 'ERR_INVALID_ARG_TYPE',`
	`49`	`+ name: 'TypeError'`
	`50`	`+});`

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