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</svg> 1101cb0ef41Sopenharmony_ci </button> 1111cb0ef41Sopenharmony_ci </div> 1121cb0ef41Sopenharmony_ci <div id="gtoc"> 1131cb0ef41Sopenharmony_ci <ul> 1141cb0ef41Sopenharmony_ci <li class="pinned-header">Node.js v18.20.1</li> 1151cb0ef41Sopenharmony_ci 1161cb0ef41Sopenharmony_ci <li class="picker-header"> 1171cb0ef41Sopenharmony_ci <a href="#"> 1181cb0ef41Sopenharmony_ci <span class="collapsed-arrow">►</span><span class="expanded-arrow">▼</span> 1191cb0ef41Sopenharmony_ci Table of contents 1201cb0ef41Sopenharmony_ci </a> 1211cb0ef41Sopenharmony_ci 1221cb0ef41Sopenharmony_ci <div class="picker"><div class="toc"><ul> 1231cb0ef41Sopenharmony_ci<li><span class="stability_2"><a href="#asynchronous-context-tracking">Asynchronous context tracking</a></span> 1241cb0ef41Sopenharmony_ci<ul> 1251cb0ef41Sopenharmony_ci<li><a href="#introduction">Introduction</a></li> 1261cb0ef41Sopenharmony_ci<li><a href="#class-asynclocalstorage">Class: <code>AsyncLocalStorage</code></a> 1271cb0ef41Sopenharmony_ci<ul> 1281cb0ef41Sopenharmony_ci<li><a href="#new-asynclocalstorage"><code>new AsyncLocalStorage()</code></a></li> 1291cb0ef41Sopenharmony_ci<li><span class="stability_1"><a href="#static-method-asynclocalstoragebindfn">Static method: <code>AsyncLocalStorage.bind(fn)</code></a></span></li> 1301cb0ef41Sopenharmony_ci<li><span class="stability_1"><a href="#static-method-asynclocalstoragesnapshot">Static method: <code>AsyncLocalStorage.snapshot()</code></a></span></li> 1311cb0ef41Sopenharmony_ci<li><span class="stability_1"><a href="#asynclocalstoragedisable"><code>asyncLocalStorage.disable()</code></a></span></li> 1321cb0ef41Sopenharmony_ci<li><a href="#asynclocalstoragegetstore"><code>asyncLocalStorage.getStore()</code></a></li> 1331cb0ef41Sopenharmony_ci<li><span class="stability_1"><a href="#asynclocalstorageenterwithstore"><code>asyncLocalStorage.enterWith(store)</code></a></span></li> 1341cb0ef41Sopenharmony_ci<li><a href="#asynclocalstoragerunstore-callback-args"><code>asyncLocalStorage.run(store, callback[, ...args])</code></a></li> 1351cb0ef41Sopenharmony_ci<li><span class="stability_1"><a href="#asynclocalstorageexitcallback-args"><code>asyncLocalStorage.exit(callback[, ...args])</code></a></span></li> 1361cb0ef41Sopenharmony_ci<li><a href="#usage-with-asyncawait">Usage with <code>async/await</code></a></li> 1371cb0ef41Sopenharmony_ci<li><a href="#troubleshooting-context-loss">Troubleshooting: Context loss</a></li> 1381cb0ef41Sopenharmony_ci</ul> 1391cb0ef41Sopenharmony_ci</li> 1401cb0ef41Sopenharmony_ci<li><a href="#class-asyncresource">Class: <code>AsyncResource</code></a> 1411cb0ef41Sopenharmony_ci<ul> 1421cb0ef41Sopenharmony_ci<li><a href="#new-asyncresourcetype-options"><code>new AsyncResource(type[, options])</code></a></li> 1431cb0ef41Sopenharmony_ci<li><a href="#static-method-asyncresourcebindfn-type-thisarg">Static method: <code>AsyncResource.bind(fn[, type[, thisArg]])</code></a></li> 1441cb0ef41Sopenharmony_ci<li><a href="#asyncresourcebindfn-thisarg"><code>asyncResource.bind(fn[, thisArg])</code></a></li> 1451cb0ef41Sopenharmony_ci<li><a href="#asyncresourceruninasyncscopefn-thisarg-args"><code>asyncResource.runInAsyncScope(fn[, thisArg, ...args])</code></a></li> 1461cb0ef41Sopenharmony_ci<li><a href="#asyncresourceemitdestroy"><code>asyncResource.emitDestroy()</code></a></li> 1471cb0ef41Sopenharmony_ci<li><a href="#asyncresourceasyncid"><code>asyncResource.asyncId()</code></a></li> 1481cb0ef41Sopenharmony_ci<li><a href="#asyncresourcetriggerasyncid"><code>asyncResource.triggerAsyncId()</code></a></li> 1491cb0ef41Sopenharmony_ci<li><a href="#using-asyncresource-for-a-worker-thread-pool">Using <code>AsyncResource</code> for a <code>Worker</code> thread pool</a></li> 1501cb0ef41Sopenharmony_ci<li><a href="#integrating-asyncresource-with-eventemitter">Integrating <code>AsyncResource</code> with <code>EventEmitter</code></a></li> 1511cb0ef41Sopenharmony_ci</ul> 1521cb0ef41Sopenharmony_ci</li> 1531cb0ef41Sopenharmony_ci</ul> 1541cb0ef41Sopenharmony_ci</li> 1551cb0ef41Sopenharmony_ci</ul></div></div> 1561cb0ef41Sopenharmony_ci </li> 1571cb0ef41Sopenharmony_ci 1581cb0ef41Sopenharmony_ci 1591cb0ef41Sopenharmony_ci <li class="picker-header"> 1601cb0ef41Sopenharmony_ci <a href="#"> 1611cb0ef41Sopenharmony_ci <span class="collapsed-arrow">►</span><span class="expanded-arrow">▼</span> 1621cb0ef41Sopenharmony_ci Index 1631cb0ef41Sopenharmony_ci </a> 1641cb0ef41Sopenharmony_ci 1651cb0ef41Sopenharmony_ci <div class="picker"><ul> 1661cb0ef41Sopenharmony_ci<li><a href="documentation.html" class="nav-documentation">About this documentation</a></li> 1671cb0ef41Sopenharmony_ci<li><a href="synopsis.html" class="nav-synopsis">Usage and example</a></li> 1681cb0ef41Sopenharmony_ci 1691cb0ef41Sopenharmony_ci <li> 1701cb0ef41Sopenharmony_ci <a href="index.html">Index</a> 1711cb0ef41Sopenharmony_ci </li> 1721cb0ef41Sopenharmony_ci </ul> 1731cb0ef41Sopenharmony_ci 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2531cb0ef41Sopenharmony_ci<li><a href="https://nodejs.org/docs/latest-v17.x/api/async_context.html">17.x</a></li> 2541cb0ef41Sopenharmony_ci<li><a href="https://nodejs.org/docs/latest-v16.x/api/async_context.html">16.x</a></li></ol></div> 2551cb0ef41Sopenharmony_ci </li> 2561cb0ef41Sopenharmony_ci 2571cb0ef41Sopenharmony_ci <li class="picker-header"> 2581cb0ef41Sopenharmony_ci <a href="#"> 2591cb0ef41Sopenharmony_ci <span class="collapsed-arrow">►</span><span class="expanded-arrow">▼</span> 2601cb0ef41Sopenharmony_ci Options 2611cb0ef41Sopenharmony_ci </a> 2621cb0ef41Sopenharmony_ci 2631cb0ef41Sopenharmony_ci <div class="picker"> 2641cb0ef41Sopenharmony_ci <ul> 2651cb0ef41Sopenharmony_ci <li> 2661cb0ef41Sopenharmony_ci <a href="all.html">View on single page</a> 2671cb0ef41Sopenharmony_ci </li> 2681cb0ef41Sopenharmony_ci <li> 2691cb0ef41Sopenharmony_ci <a href="async_context.json">View as JSON</a> 2701cb0ef41Sopenharmony_ci </li> 2711cb0ef41Sopenharmony_ci <li class="edit_on_github"><a href="https://github.com/nodejs/node/edit/main/doc/api/async_context.md">Edit on GitHub</a></li> 2721cb0ef41Sopenharmony_ci </ul> 2731cb0ef41Sopenharmony_ci </div> 2741cb0ef41Sopenharmony_ci </li> 2751cb0ef41Sopenharmony_ci </ul> 2761cb0ef41Sopenharmony_ci </div> 2771cb0ef41Sopenharmony_ci <hr> 2781cb0ef41Sopenharmony_ci </header> 2791cb0ef41Sopenharmony_ci 2801cb0ef41Sopenharmony_ci <details id="toc" open><summary>Table of contents</summary><ul> 2811cb0ef41Sopenharmony_ci<li><span class="stability_2"><a href="#asynchronous-context-tracking">Asynchronous context tracking</a></span> 2821cb0ef41Sopenharmony_ci<ul> 2831cb0ef41Sopenharmony_ci<li><a href="#introduction">Introduction</a></li> 2841cb0ef41Sopenharmony_ci<li><a href="#class-asynclocalstorage">Class: <code>AsyncLocalStorage</code></a> 2851cb0ef41Sopenharmony_ci<ul> 2861cb0ef41Sopenharmony_ci<li><a href="#new-asynclocalstorage"><code>new AsyncLocalStorage()</code></a></li> 2871cb0ef41Sopenharmony_ci<li><span class="stability_1"><a href="#static-method-asynclocalstoragebindfn">Static method: <code>AsyncLocalStorage.bind(fn)</code></a></span></li> 2881cb0ef41Sopenharmony_ci<li><span class="stability_1"><a href="#static-method-asynclocalstoragesnapshot">Static method: <code>AsyncLocalStorage.snapshot()</code></a></span></li> 2891cb0ef41Sopenharmony_ci<li><span class="stability_1"><a href="#asynclocalstoragedisable"><code>asyncLocalStorage.disable()</code></a></span></li> 2901cb0ef41Sopenharmony_ci<li><a href="#asynclocalstoragegetstore"><code>asyncLocalStorage.getStore()</code></a></li> 2911cb0ef41Sopenharmony_ci<li><span class="stability_1"><a href="#asynclocalstorageenterwithstore"><code>asyncLocalStorage.enterWith(store)</code></a></span></li> 2921cb0ef41Sopenharmony_ci<li><a href="#asynclocalstoragerunstore-callback-args"><code>asyncLocalStorage.run(store, callback[, ...args])</code></a></li> 2931cb0ef41Sopenharmony_ci<li><span class="stability_1"><a href="#asynclocalstorageexitcallback-args"><code>asyncLocalStorage.exit(callback[, ...args])</code></a></span></li> 2941cb0ef41Sopenharmony_ci<li><a href="#usage-with-asyncawait">Usage with <code>async/await</code></a></li> 2951cb0ef41Sopenharmony_ci<li><a href="#troubleshooting-context-loss">Troubleshooting: Context loss</a></li> 2961cb0ef41Sopenharmony_ci</ul> 2971cb0ef41Sopenharmony_ci</li> 2981cb0ef41Sopenharmony_ci<li><a href="#class-asyncresource">Class: <code>AsyncResource</code></a> 2991cb0ef41Sopenharmony_ci<ul> 3001cb0ef41Sopenharmony_ci<li><a href="#new-asyncresourcetype-options"><code>new AsyncResource(type[, options])</code></a></li> 3011cb0ef41Sopenharmony_ci<li><a href="#static-method-asyncresourcebindfn-type-thisarg">Static method: <code>AsyncResource.bind(fn[, type[, thisArg]])</code></a></li> 3021cb0ef41Sopenharmony_ci<li><a href="#asyncresourcebindfn-thisarg"><code>asyncResource.bind(fn[, thisArg])</code></a></li> 3031cb0ef41Sopenharmony_ci<li><a href="#asyncresourceruninasyncscopefn-thisarg-args"><code>asyncResource.runInAsyncScope(fn[, thisArg, ...args])</code></a></li> 3041cb0ef41Sopenharmony_ci<li><a href="#asyncresourceemitdestroy"><code>asyncResource.emitDestroy()</code></a></li> 3051cb0ef41Sopenharmony_ci<li><a href="#asyncresourceasyncid"><code>asyncResource.asyncId()</code></a></li> 3061cb0ef41Sopenharmony_ci<li><a href="#asyncresourcetriggerasyncid"><code>asyncResource.triggerAsyncId()</code></a></li> 3071cb0ef41Sopenharmony_ci<li><a href="#using-asyncresource-for-a-worker-thread-pool">Using <code>AsyncResource</code> for a <code>Worker</code> thread pool</a></li> 3081cb0ef41Sopenharmony_ci<li><a href="#integrating-asyncresource-with-eventemitter">Integrating <code>AsyncResource</code> with <code>EventEmitter</code></a></li> 3091cb0ef41Sopenharmony_ci</ul> 3101cb0ef41Sopenharmony_ci</li> 3111cb0ef41Sopenharmony_ci</ul> 3121cb0ef41Sopenharmony_ci</li> 3131cb0ef41Sopenharmony_ci</ul></details> 3141cb0ef41Sopenharmony_ci 3151cb0ef41Sopenharmony_ci <div id="apicontent"> 3161cb0ef41Sopenharmony_ci <h2>Asynchronous context tracking<span><a class="mark" href="#asynchronous-context-tracking" id="asynchronous-context-tracking">#</a></span><a aria-hidden="true" class="legacy" id="async_context_asynchronous_context_tracking"></a></h2> 3171cb0ef41Sopenharmony_ci 3181cb0ef41Sopenharmony_ci<p></p><div class="api_stability api_stability_2"><a href="documentation.html#stability-index">Stability: 2</a> - Stable</div><p></p> 3191cb0ef41Sopenharmony_ci<p><strong>Source Code:</strong> <a href="https://github.com/nodejs/node/blob/v18.20.1/lib/async_hooks.js">lib/async_hooks.js</a></p> 3201cb0ef41Sopenharmony_ci<section><h3>Introduction<span><a class="mark" href="#introduction" id="introduction">#</a></span><a aria-hidden="true" class="legacy" id="async_context_introduction"></a></h3> 3211cb0ef41Sopenharmony_ci<p>These classes are used to associate state and propagate it throughout 3221cb0ef41Sopenharmony_cicallbacks and promise chains. 3231cb0ef41Sopenharmony_ciThey allow storing data throughout the lifetime of a web request 3241cb0ef41Sopenharmony_cior any other asynchronous duration. It is similar to thread-local storage 3251cb0ef41Sopenharmony_ciin other languages.</p> 3261cb0ef41Sopenharmony_ci<p>The <code>AsyncLocalStorage</code> and <code>AsyncResource</code> classes are part of the 3271cb0ef41Sopenharmony_ci<code>node:async_hooks</code> module:</p> 3281cb0ef41Sopenharmony_ci 3291cb0ef41Sopenharmony_ci<pre class="with-73-chars"><input class="js-flavor-selector" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> { <span class="hljs-title class_">AsyncLocalStorage</span>, <span class="hljs-title class_">AsyncResource</span> } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:async_hooks'</span>;</code><code class="language-js cjs"><span class="hljs-keyword">const</span> { <span class="hljs-title class_">AsyncLocalStorage</span>, <span class="hljs-title class_">AsyncResource</span> } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:async_hooks'</span>);</code><button class="copy-button">copy</button></pre> 3301cb0ef41Sopenharmony_ci</section><section><h3>Class: <code>AsyncLocalStorage</code><span><a class="mark" href="#class-asynclocalstorage" id="class-asynclocalstorage">#</a></span><a aria-hidden="true" class="legacy" id="async_context_class_asynclocalstorage"></a></h3> 3311cb0ef41Sopenharmony_ci<div class="api_metadata"> 3321cb0ef41Sopenharmony_ci<details class="changelog"><summary>History</summary> 3331cb0ef41Sopenharmony_ci<table> 3341cb0ef41Sopenharmony_ci<tbody><tr><th>Version</th><th>Changes</th></tr> 3351cb0ef41Sopenharmony_ci<tr><td>v16.4.0</td> 3361cb0ef41Sopenharmony_ci<td><p>AsyncLocalStorage is now Stable. Previously, it had been Experimental.</p></td></tr> 3371cb0ef41Sopenharmony_ci<tr><td>v13.10.0, v12.17.0</td> 3381cb0ef41Sopenharmony_ci<td><p><span>Added in: v13.10.0, v12.17.0</span></p></td></tr> 3391cb0ef41Sopenharmony_ci</tbody></table> 3401cb0ef41Sopenharmony_ci</details> 3411cb0ef41Sopenharmony_ci</div> 3421cb0ef41Sopenharmony_ci<p>This class creates stores that stay coherent through asynchronous operations.</p> 3431cb0ef41Sopenharmony_ci<p>While you can create your own implementation on top of the <code>node:async_hooks</code> 3441cb0ef41Sopenharmony_cimodule, <code>AsyncLocalStorage</code> should be preferred as it is a performant and memory 3451cb0ef41Sopenharmony_cisafe implementation that involves significant optimizations that are non-obvious 3461cb0ef41Sopenharmony_cito implement.</p> 3471cb0ef41Sopenharmony_ci<p>The following example uses <code>AsyncLocalStorage</code> to build a simple logger 3481cb0ef41Sopenharmony_cithat assigns IDs to incoming HTTP requests and includes them in messages 3491cb0ef41Sopenharmony_cilogged within each request.</p> 3501cb0ef41Sopenharmony_ci 3511cb0ef41Sopenharmony_ci<pre class="with-58-chars"><input class="js-flavor-selector" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> http <span class="hljs-keyword">from</span> <span class="hljs-string">'node:http'</span>; 3521cb0ef41Sopenharmony_ci<span class="hljs-keyword">import</span> { <span class="hljs-title class_">AsyncLocalStorage</span> } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:async_hooks'</span>; 3531cb0ef41Sopenharmony_ci 3541cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> asyncLocalStorage = <span class="hljs-keyword">new</span> <span class="hljs-title class_">AsyncLocalStorage</span>(); 3551cb0ef41Sopenharmony_ci 3561cb0ef41Sopenharmony_ci<span class="hljs-keyword">function</span> <span class="hljs-title function_">logWithId</span>(<span class="hljs-params">msg</span>) { 3571cb0ef41Sopenharmony_ci <span class="hljs-keyword">const</span> id = asyncLocalStorage.<span class="hljs-title function_">getStore</span>(); 3581cb0ef41Sopenharmony_ci <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">`<span class="hljs-subst">${id !== <span class="hljs-literal">undefined</span> ? id : <span class="hljs-string">'-'</span>}</span>:`</span>, msg); 3591cb0ef41Sopenharmony_ci} 3601cb0ef41Sopenharmony_ci 3611cb0ef41Sopenharmony_ci<span class="hljs-keyword">let</span> idSeq = <span class="hljs-number">0</span>; 3621cb0ef41Sopenharmony_cihttp.<span class="hljs-title function_">createServer</span>(<span class="hljs-function">(<span class="hljs-params">req, res</span>) =></span> { 3631cb0ef41Sopenharmony_ci asyncLocalStorage.<span class="hljs-title function_">run</span>(idSeq++, <span class="hljs-function">() =></span> { 3641cb0ef41Sopenharmony_ci <span class="hljs-title function_">logWithId</span>(<span class="hljs-string">'start'</span>); 3651cb0ef41Sopenharmony_ci <span class="hljs-comment">// Imagine any chain of async operations here</span> 3661cb0ef41Sopenharmony_ci <span class="hljs-title function_">setImmediate</span>(<span class="hljs-function">() =></span> { 3671cb0ef41Sopenharmony_ci <span class="hljs-title function_">logWithId</span>(<span class="hljs-string">'finish'</span>); 3681cb0ef41Sopenharmony_ci res.<span class="hljs-title function_">end</span>(); 3691cb0ef41Sopenharmony_ci }); 3701cb0ef41Sopenharmony_ci }); 3711cb0ef41Sopenharmony_ci}).<span class="hljs-title function_">listen</span>(<span class="hljs-number">8080</span>); 3721cb0ef41Sopenharmony_ci 3731cb0ef41Sopenharmony_cihttp.<span class="hljs-title function_">get</span>(<span class="hljs-string">'http://localhost:8080'</span>); 3741cb0ef41Sopenharmony_cihttp.<span class="hljs-title function_">get</span>(<span class="hljs-string">'http://localhost:8080'</span>); 3751cb0ef41Sopenharmony_ci<span class="hljs-comment">// Prints:</span> 3761cb0ef41Sopenharmony_ci<span class="hljs-comment">// 0: start</span> 3771cb0ef41Sopenharmony_ci<span class="hljs-comment">// 1: start</span> 3781cb0ef41Sopenharmony_ci<span class="hljs-comment">// 0: finish</span> 3791cb0ef41Sopenharmony_ci<span class="hljs-comment">// 1: finish</span></code><code class="language-js cjs"><span class="hljs-keyword">const</span> http = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:http'</span>); 3801cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> { <span class="hljs-title class_">AsyncLocalStorage</span> } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:async_hooks'</span>); 3811cb0ef41Sopenharmony_ci 3821cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> asyncLocalStorage = <span class="hljs-keyword">new</span> <span class="hljs-title class_">AsyncLocalStorage</span>(); 3831cb0ef41Sopenharmony_ci 3841cb0ef41Sopenharmony_ci<span class="hljs-keyword">function</span> <span class="hljs-title function_">logWithId</span>(<span class="hljs-params">msg</span>) { 3851cb0ef41Sopenharmony_ci <span class="hljs-keyword">const</span> id = asyncLocalStorage.<span class="hljs-title function_">getStore</span>(); 3861cb0ef41Sopenharmony_ci <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">`<span class="hljs-subst">${id !== <span class="hljs-literal">undefined</span> ? id : <span class="hljs-string">'-'</span>}</span>:`</span>, msg); 3871cb0ef41Sopenharmony_ci} 3881cb0ef41Sopenharmony_ci 3891cb0ef41Sopenharmony_ci<span class="hljs-keyword">let</span> idSeq = <span class="hljs-number">0</span>; 3901cb0ef41Sopenharmony_cihttp.<span class="hljs-title function_">createServer</span>(<span class="hljs-function">(<span class="hljs-params">req, res</span>) =></span> { 3911cb0ef41Sopenharmony_ci asyncLocalStorage.<span class="hljs-title function_">run</span>(idSeq++, <span class="hljs-function">() =></span> { 3921cb0ef41Sopenharmony_ci <span class="hljs-title function_">logWithId</span>(<span class="hljs-string">'start'</span>); 3931cb0ef41Sopenharmony_ci <span class="hljs-comment">// Imagine any chain of async operations here</span> 3941cb0ef41Sopenharmony_ci <span class="hljs-title function_">setImmediate</span>(<span class="hljs-function">() =></span> { 3951cb0ef41Sopenharmony_ci <span class="hljs-title function_">logWithId</span>(<span class="hljs-string">'finish'</span>); 3961cb0ef41Sopenharmony_ci res.<span class="hljs-title function_">end</span>(); 3971cb0ef41Sopenharmony_ci }); 3981cb0ef41Sopenharmony_ci }); 3991cb0ef41Sopenharmony_ci}).<span class="hljs-title function_">listen</span>(<span class="hljs-number">8080</span>); 4001cb0ef41Sopenharmony_ci 4011cb0ef41Sopenharmony_cihttp.<span class="hljs-title function_">get</span>(<span class="hljs-string">'http://localhost:8080'</span>); 4021cb0ef41Sopenharmony_cihttp.<span class="hljs-title function_">get</span>(<span class="hljs-string">'http://localhost:8080'</span>); 4031cb0ef41Sopenharmony_ci<span class="hljs-comment">// Prints:</span> 4041cb0ef41Sopenharmony_ci<span class="hljs-comment">// 0: start</span> 4051cb0ef41Sopenharmony_ci<span class="hljs-comment">// 1: start</span> 4061cb0ef41Sopenharmony_ci<span class="hljs-comment">// 0: finish</span> 4071cb0ef41Sopenharmony_ci<span class="hljs-comment">// 1: finish</span></code><button class="copy-button">copy</button></pre> 4081cb0ef41Sopenharmony_ci<p>Each instance of <code>AsyncLocalStorage</code> maintains an independent storage context. 4091cb0ef41Sopenharmony_ciMultiple instances can safely exist simultaneously without risk of interfering 4101cb0ef41Sopenharmony_ciwith each other's data.</p> 4111cb0ef41Sopenharmony_ci<h4><code>new AsyncLocalStorage()</code><span><a class="mark" href="#new-asynclocalstorage" id="new-asynclocalstorage">#</a></span><a aria-hidden="true" class="legacy" id="async_context_new_asynclocalstorage"></a></h4> 4121cb0ef41Sopenharmony_ci<div class="api_metadata"> 4131cb0ef41Sopenharmony_ci<details class="changelog"><summary>History</summary> 4141cb0ef41Sopenharmony_ci<table> 4151cb0ef41Sopenharmony_ci<tbody><tr><th>Version</th><th>Changes</th></tr> 4161cb0ef41Sopenharmony_ci<tr><td>v18.16.0</td> 4171cb0ef41Sopenharmony_ci<td><p>Removed experimental onPropagate option.</p></td></tr> 4181cb0ef41Sopenharmony_ci<tr><td>v18.13.0</td> 4191cb0ef41Sopenharmony_ci<td><p>Add option onPropagate.</p></td></tr> 4201cb0ef41Sopenharmony_ci<tr><td>v13.10.0, v12.17.0</td> 4211cb0ef41Sopenharmony_ci<td><p><span>Added in: v13.10.0, v12.17.0</span></p></td></tr> 4221cb0ef41Sopenharmony_ci</tbody></table> 4231cb0ef41Sopenharmony_ci</details> 4241cb0ef41Sopenharmony_ci</div> 4251cb0ef41Sopenharmony_ci<p>Creates a new instance of <code>AsyncLocalStorage</code>. Store is only provided within a 4261cb0ef41Sopenharmony_ci<code>run()</code> call or after an <code>enterWith()</code> call.</p> 4271cb0ef41Sopenharmony_ci<h4>Static method: <code>AsyncLocalStorage.bind(fn)</code><span><a class="mark" href="#static-method-asynclocalstoragebindfn" id="static-method-asynclocalstoragebindfn">#</a></span><a aria-hidden="true" class="legacy" id="async_context_static_method_asynclocalstorage_bind_fn"></a></h4> 4281cb0ef41Sopenharmony_ci<div class="api_metadata"> 4291cb0ef41Sopenharmony_ci<span>Added in: v18.16.0</span> 4301cb0ef41Sopenharmony_ci</div> 4311cb0ef41Sopenharmony_ci<p></p><div class="api_stability api_stability_1"><a href="documentation.html#stability-index">Stability: 1</a> - Experimental</div><p></p> 4321cb0ef41Sopenharmony_ci<ul> 4331cb0ef41Sopenharmony_ci<li><code>fn</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> The function to bind to the current execution context.</li> 4341cb0ef41Sopenharmony_ci<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> A new function that calls <code>fn</code> within the captured 4351cb0ef41Sopenharmony_ciexecution context.</li> 4361cb0ef41Sopenharmony_ci</ul> 4371cb0ef41Sopenharmony_ci<p>Binds the given function to the current execution context.</p> 4381cb0ef41Sopenharmony_ci<h4>Static method: <code>AsyncLocalStorage.snapshot()</code><span><a class="mark" href="#static-method-asynclocalstoragesnapshot" id="static-method-asynclocalstoragesnapshot">#</a></span><a aria-hidden="true" class="legacy" id="async_context_static_method_asynclocalstorage_snapshot"></a></h4> 4391cb0ef41Sopenharmony_ci<div class="api_metadata"> 4401cb0ef41Sopenharmony_ci<span>Added in: v18.16.0</span> 4411cb0ef41Sopenharmony_ci</div> 4421cb0ef41Sopenharmony_ci<p></p><div class="api_stability api_stability_1"><a href="documentation.html#stability-index">Stability: 1</a> - Experimental</div><p></p> 4431cb0ef41Sopenharmony_ci<ul> 4441cb0ef41Sopenharmony_ci<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> A new function with the signature 4451cb0ef41Sopenharmony_ci<code>(fn: (...args) : R, ...args) : R</code>.</li> 4461cb0ef41Sopenharmony_ci</ul> 4471cb0ef41Sopenharmony_ci<p>Captures the current execution context and returns a function that accepts a 4481cb0ef41Sopenharmony_cifunction as an argument. Whenever the returned function is called, it 4491cb0ef41Sopenharmony_cicalls the function passed to it within the captured context.</p> 4501cb0ef41Sopenharmony_ci<pre><code class="language-js"><span class="hljs-keyword">const</span> asyncLocalStorage = <span class="hljs-keyword">new</span> <span class="hljs-title class_">AsyncLocalStorage</span>(); 4511cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> runInAsyncScope = asyncLocalStorage.<span class="hljs-title function_">run</span>(<span class="hljs-number">123</span>, <span class="hljs-function">() =></span> <span class="hljs-title class_">AsyncLocalStorage</span>.<span class="hljs-title function_">snapshot</span>()); 4521cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> result = asyncLocalStorage.<span class="hljs-title function_">run</span>(<span class="hljs-number">321</span>, <span class="hljs-function">() =></span> <span class="hljs-title function_">runInAsyncScope</span>(<span class="hljs-function">() =></span> asyncLocalStorage.<span class="hljs-title function_">getStore</span>())); 4531cb0ef41Sopenharmony_ci<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(result); <span class="hljs-comment">// returns 123</span></code> <button class="copy-button">copy</button></pre> 4541cb0ef41Sopenharmony_ci<p>AsyncLocalStorage.snapshot() can replace the use of AsyncResource for simple 4551cb0ef41Sopenharmony_ciasync context tracking purposes, for example:</p> 4561cb0ef41Sopenharmony_ci<pre><code class="language-js"><span class="hljs-keyword">class</span> <span class="hljs-title class_">Foo</span> { 4571cb0ef41Sopenharmony_ci #runInAsyncScope = <span class="hljs-title class_">AsyncLocalStorage</span>.<span class="hljs-title function_">snapshot</span>(); 4581cb0ef41Sopenharmony_ci 4591cb0ef41Sopenharmony_ci <span class="hljs-title function_">get</span>(<span class="hljs-params"></span>) { <span class="hljs-keyword">return</span> <span class="hljs-variable language_">this</span>.#<span class="hljs-title function_">runInAsyncScope</span>(<span class="hljs-function">() =></span> asyncLocalStorage.<span class="hljs-title function_">getStore</span>()); } 4601cb0ef41Sopenharmony_ci} 4611cb0ef41Sopenharmony_ci 4621cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> foo = asyncLocalStorage.<span class="hljs-title function_">run</span>(<span class="hljs-number">123</span>, <span class="hljs-function">() =></span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">Foo</span>()); 4631cb0ef41Sopenharmony_ci<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(asyncLocalStorage.<span class="hljs-title function_">run</span>(<span class="hljs-number">321</span>, <span class="hljs-function">() =></span> foo.<span class="hljs-title function_">get</span>())); <span class="hljs-comment">// returns 123</span></code> <button class="copy-button">copy</button></pre> 4641cb0ef41Sopenharmony_ci<h4><code>asyncLocalStorage.disable()</code><span><a class="mark" href="#asynclocalstoragedisable" id="asynclocalstoragedisable">#</a></span><a aria-hidden="true" class="legacy" id="async_context_asynclocalstorage_disable"></a></h4> 4651cb0ef41Sopenharmony_ci<div class="api_metadata"> 4661cb0ef41Sopenharmony_ci<span>Added in: v13.10.0, v12.17.0</span> 4671cb0ef41Sopenharmony_ci</div> 4681cb0ef41Sopenharmony_ci<p></p><div class="api_stability api_stability_1"><a href="documentation.html#stability-index">Stability: 1</a> - Experimental</div><p></p> 4691cb0ef41Sopenharmony_ci<p>Disables the instance of <code>AsyncLocalStorage</code>. All subsequent calls 4701cb0ef41Sopenharmony_cito <code>asyncLocalStorage.getStore()</code> will return <code>undefined</code> until 4711cb0ef41Sopenharmony_ci<code>asyncLocalStorage.run()</code> or <code>asyncLocalStorage.enterWith()</code> is called again.</p> 4721cb0ef41Sopenharmony_ci<p>When calling <code>asyncLocalStorage.disable()</code>, all current contexts linked to the 4731cb0ef41Sopenharmony_ciinstance will be exited.</p> 4741cb0ef41Sopenharmony_ci<p>Calling <code>asyncLocalStorage.disable()</code> is required before the 4751cb0ef41Sopenharmony_ci<code>asyncLocalStorage</code> can be garbage collected. This does not apply to stores 4761cb0ef41Sopenharmony_ciprovided by the <code>asyncLocalStorage</code>, as those objects are garbage collected 4771cb0ef41Sopenharmony_cialong with the corresponding async resources.</p> 4781cb0ef41Sopenharmony_ci<p>Use this method when the <code>asyncLocalStorage</code> is not in use anymore 4791cb0ef41Sopenharmony_ciin the current process.</p> 4801cb0ef41Sopenharmony_ci<h4><code>asyncLocalStorage.getStore()</code><span><a class="mark" href="#asynclocalstoragegetstore" id="asynclocalstoragegetstore">#</a></span><a aria-hidden="true" class="legacy" id="async_context_asynclocalstorage_getstore"></a></h4> 4811cb0ef41Sopenharmony_ci<div class="api_metadata"> 4821cb0ef41Sopenharmony_ci<span>Added in: v13.10.0, v12.17.0</span> 4831cb0ef41Sopenharmony_ci</div> 4841cb0ef41Sopenharmony_ci<ul> 4851cb0ef41Sopenharmony_ci<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> 4861cb0ef41Sopenharmony_ci</ul> 4871cb0ef41Sopenharmony_ci<p>Returns the current store. 4881cb0ef41Sopenharmony_ciIf called outside of an asynchronous context initialized by 4891cb0ef41Sopenharmony_cicalling <code>asyncLocalStorage.run()</code> or <code>asyncLocalStorage.enterWith()</code>, it 4901cb0ef41Sopenharmony_cireturns <code>undefined</code>.</p> 4911cb0ef41Sopenharmony_ci<h4><code>asyncLocalStorage.enterWith(store)</code><span><a class="mark" href="#asynclocalstorageenterwithstore" id="asynclocalstorageenterwithstore">#</a></span><a aria-hidden="true" class="legacy" id="async_context_asynclocalstorage_enterwith_store"></a></h4> 4921cb0ef41Sopenharmony_ci<div class="api_metadata"> 4931cb0ef41Sopenharmony_ci<span>Added in: v13.11.0, v12.17.0</span> 4941cb0ef41Sopenharmony_ci</div> 4951cb0ef41Sopenharmony_ci<p></p><div class="api_stability api_stability_1"><a href="documentation.html#stability-index">Stability: 1</a> - Experimental</div><p></p> 4961cb0ef41Sopenharmony_ci<ul> 4971cb0ef41Sopenharmony_ci<li><code>store</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> 4981cb0ef41Sopenharmony_ci</ul> 4991cb0ef41Sopenharmony_ci<p>Transitions into the context for the remainder of the current 5001cb0ef41Sopenharmony_cisynchronous execution and then persists the store through any following 5011cb0ef41Sopenharmony_ciasynchronous calls.</p> 5021cb0ef41Sopenharmony_ci<p>Example:</p> 5031cb0ef41Sopenharmony_ci<pre><code class="language-js"><span class="hljs-keyword">const</span> store = { <span class="hljs-attr">id</span>: <span class="hljs-number">1</span> }; 5041cb0ef41Sopenharmony_ci<span class="hljs-comment">// Replaces previous store with the given store object</span> 5051cb0ef41Sopenharmony_ciasyncLocalStorage.<span class="hljs-title function_">enterWith</span>(store); 5061cb0ef41Sopenharmony_ciasyncLocalStorage.<span class="hljs-title function_">getStore</span>(); <span class="hljs-comment">// Returns the store object</span> 5071cb0ef41Sopenharmony_ci<span class="hljs-title function_">someAsyncOperation</span>(<span class="hljs-function">() =></span> { 5081cb0ef41Sopenharmony_ci asyncLocalStorage.<span class="hljs-title function_">getStore</span>(); <span class="hljs-comment">// Returns the same object</span> 5091cb0ef41Sopenharmony_ci});</code> <button class="copy-button">copy</button></pre> 5101cb0ef41Sopenharmony_ci<p>This transition will continue for the <em>entire</em> synchronous execution. 5111cb0ef41Sopenharmony_ciThis means that if, for example, the context is entered within an event 5121cb0ef41Sopenharmony_cihandler subsequent event handlers will also run within that context unless 5131cb0ef41Sopenharmony_cispecifically bound to another context with an <code>AsyncResource</code>. That is why 5141cb0ef41Sopenharmony_ci<code>run()</code> should be preferred over <code>enterWith()</code> unless there are strong reasons 5151cb0ef41Sopenharmony_cito use the latter method.</p> 5161cb0ef41Sopenharmony_ci<pre><code class="language-js"><span class="hljs-keyword">const</span> store = { <span class="hljs-attr">id</span>: <span class="hljs-number">1</span> }; 5171cb0ef41Sopenharmony_ci 5181cb0ef41Sopenharmony_ciemitter.<span class="hljs-title function_">on</span>(<span class="hljs-string">'my-event'</span>, <span class="hljs-function">() =></span> { 5191cb0ef41Sopenharmony_ci asyncLocalStorage.<span class="hljs-title function_">enterWith</span>(store); 5201cb0ef41Sopenharmony_ci}); 5211cb0ef41Sopenharmony_ciemitter.<span class="hljs-title function_">on</span>(<span class="hljs-string">'my-event'</span>, <span class="hljs-function">() =></span> { 5221cb0ef41Sopenharmony_ci asyncLocalStorage.<span class="hljs-title function_">getStore</span>(); <span class="hljs-comment">// Returns the same object</span> 5231cb0ef41Sopenharmony_ci}); 5241cb0ef41Sopenharmony_ci 5251cb0ef41Sopenharmony_ciasyncLocalStorage.<span class="hljs-title function_">getStore</span>(); <span class="hljs-comment">// Returns undefined</span> 5261cb0ef41Sopenharmony_ciemitter.<span class="hljs-title function_">emit</span>(<span class="hljs-string">'my-event'</span>); 5271cb0ef41Sopenharmony_ciasyncLocalStorage.<span class="hljs-title function_">getStore</span>(); <span class="hljs-comment">// Returns the same object</span></code> <button class="copy-button">copy</button></pre> 5281cb0ef41Sopenharmony_ci<h4><code>asyncLocalStorage.run(store, callback[, ...args])</code><span><a class="mark" href="#asynclocalstoragerunstore-callback-args" id="asynclocalstoragerunstore-callback-args">#</a></span><a aria-hidden="true" class="legacy" id="async_context_asynclocalstorage_run_store_callback_args"></a></h4> 5291cb0ef41Sopenharmony_ci<div class="api_metadata"> 5301cb0ef41Sopenharmony_ci<span>Added in: v13.10.0, v12.17.0</span> 5311cb0ef41Sopenharmony_ci</div> 5321cb0ef41Sopenharmony_ci<ul> 5331cb0ef41Sopenharmony_ci<li><code>store</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> 5341cb0ef41Sopenharmony_ci<li><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></li> 5351cb0ef41Sopenharmony_ci<li><code>...args</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> 5361cb0ef41Sopenharmony_ci</ul> 5371cb0ef41Sopenharmony_ci<p>Runs a function synchronously within a context and returns its 5381cb0ef41Sopenharmony_cireturn value. The store is not accessible outside of the callback function. 5391cb0ef41Sopenharmony_ciThe store is accessible to any asynchronous operations created within the 5401cb0ef41Sopenharmony_cicallback.</p> 5411cb0ef41Sopenharmony_ci<p>The optional <code>args</code> are passed to the callback function.</p> 5421cb0ef41Sopenharmony_ci<p>If the callback function throws an error, the error is thrown by <code>run()</code> too. 5431cb0ef41Sopenharmony_ciThe stacktrace is not impacted by this call and the context is exited.</p> 5441cb0ef41Sopenharmony_ci<p>Example:</p> 5451cb0ef41Sopenharmony_ci<pre><code class="language-js"><span class="hljs-keyword">const</span> store = { <span class="hljs-attr">id</span>: <span class="hljs-number">2</span> }; 5461cb0ef41Sopenharmony_ci<span class="hljs-keyword">try</span> { 5471cb0ef41Sopenharmony_ci asyncLocalStorage.<span class="hljs-title function_">run</span>(store, <span class="hljs-function">() =></span> { 5481cb0ef41Sopenharmony_ci asyncLocalStorage.<span class="hljs-title function_">getStore</span>(); <span class="hljs-comment">// Returns the store object</span> 5491cb0ef41Sopenharmony_ci <span class="hljs-built_in">setTimeout</span>(<span class="hljs-function">() =></span> { 5501cb0ef41Sopenharmony_ci asyncLocalStorage.<span class="hljs-title function_">getStore</span>(); <span class="hljs-comment">// Returns the store object</span> 5511cb0ef41Sopenharmony_ci }, <span class="hljs-number">200</span>); 5521cb0ef41Sopenharmony_ci <span class="hljs-keyword">throw</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">Error</span>(); 5531cb0ef41Sopenharmony_ci }); 5541cb0ef41Sopenharmony_ci} <span class="hljs-keyword">catch</span> (e) { 5551cb0ef41Sopenharmony_ci asyncLocalStorage.<span class="hljs-title function_">getStore</span>(); <span class="hljs-comment">// Returns undefined</span> 5561cb0ef41Sopenharmony_ci <span class="hljs-comment">// The error will be caught here</span> 5571cb0ef41Sopenharmony_ci}</code> <button class="copy-button">copy</button></pre> 5581cb0ef41Sopenharmony_ci<h4><code>asyncLocalStorage.exit(callback[, ...args])</code><span><a class="mark" href="#asynclocalstorageexitcallback-args" id="asynclocalstorageexitcallback-args">#</a></span><a aria-hidden="true" class="legacy" id="async_context_asynclocalstorage_exit_callback_args"></a></h4> 5591cb0ef41Sopenharmony_ci<div class="api_metadata"> 5601cb0ef41Sopenharmony_ci<span>Added in: v13.10.0, v12.17.0</span> 5611cb0ef41Sopenharmony_ci</div> 5621cb0ef41Sopenharmony_ci<p></p><div class="api_stability api_stability_1"><a href="documentation.html#stability-index">Stability: 1</a> - Experimental</div><p></p> 5631cb0ef41Sopenharmony_ci<ul> 5641cb0ef41Sopenharmony_ci<li><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></li> 5651cb0ef41Sopenharmony_ci<li><code>...args</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> 5661cb0ef41Sopenharmony_ci</ul> 5671cb0ef41Sopenharmony_ci<p>Runs a function synchronously outside of a context and returns its 5681cb0ef41Sopenharmony_cireturn value. The store is not accessible within the callback function or 5691cb0ef41Sopenharmony_cithe asynchronous operations created within the callback. Any <code>getStore()</code> 5701cb0ef41Sopenharmony_cicall done within the callback function will always return <code>undefined</code>.</p> 5711cb0ef41Sopenharmony_ci<p>The optional <code>args</code> are passed to the callback function.</p> 5721cb0ef41Sopenharmony_ci<p>If the callback function throws an error, the error is thrown by <code>exit()</code> too. 5731cb0ef41Sopenharmony_ciThe stacktrace is not impacted by this call and the context is re-entered.</p> 5741cb0ef41Sopenharmony_ci<p>Example:</p> 5751cb0ef41Sopenharmony_ci<pre><code class="language-js"><span class="hljs-comment">// Within a call to run</span> 5761cb0ef41Sopenharmony_ci<span class="hljs-keyword">try</span> { 5771cb0ef41Sopenharmony_ci asyncLocalStorage.<span class="hljs-title function_">getStore</span>(); <span class="hljs-comment">// Returns the store object or value</span> 5781cb0ef41Sopenharmony_ci asyncLocalStorage.<span class="hljs-title function_">exit</span>(<span class="hljs-function">() =></span> { 5791cb0ef41Sopenharmony_ci asyncLocalStorage.<span class="hljs-title function_">getStore</span>(); <span class="hljs-comment">// Returns undefined</span> 5801cb0ef41Sopenharmony_ci <span class="hljs-keyword">throw</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">Error</span>(); 5811cb0ef41Sopenharmony_ci }); 5821cb0ef41Sopenharmony_ci} <span class="hljs-keyword">catch</span> (e) { 5831cb0ef41Sopenharmony_ci asyncLocalStorage.<span class="hljs-title function_">getStore</span>(); <span class="hljs-comment">// Returns the same object or value</span> 5841cb0ef41Sopenharmony_ci <span class="hljs-comment">// The error will be caught here</span> 5851cb0ef41Sopenharmony_ci}</code> <button class="copy-button">copy</button></pre> 5861cb0ef41Sopenharmony_ci<h4>Usage with <code>async/await</code><span><a class="mark" href="#usage-with-asyncawait" id="usage-with-asyncawait">#</a></span><a aria-hidden="true" class="legacy" id="async_context_usage_with_async_await"></a></h4> 5871cb0ef41Sopenharmony_ci<p>If, within an async function, only one <code>await</code> call is to run within a context, 5881cb0ef41Sopenharmony_cithe following pattern should be used:</p> 5891cb0ef41Sopenharmony_ci<pre><code class="language-js"><span class="hljs-keyword">async</span> <span class="hljs-keyword">function</span> <span class="hljs-title function_">fn</span>(<span class="hljs-params"></span>) { 5901cb0ef41Sopenharmony_ci <span class="hljs-keyword">await</span> asyncLocalStorage.<span class="hljs-title function_">run</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Map</span>(), <span class="hljs-function">() =></span> { 5911cb0ef41Sopenharmony_ci asyncLocalStorage.<span class="hljs-title function_">getStore</span>().<span class="hljs-title function_">set</span>(<span class="hljs-string">'key'</span>, value); 5921cb0ef41Sopenharmony_ci <span class="hljs-keyword">return</span> <span class="hljs-title function_">foo</span>(); <span class="hljs-comment">// The return value of foo will be awaited</span> 5931cb0ef41Sopenharmony_ci }); 5941cb0ef41Sopenharmony_ci}</code> <button class="copy-button">copy</button></pre> 5951cb0ef41Sopenharmony_ci<p>In this example, the store is only available in the callback function and the 5961cb0ef41Sopenharmony_cifunctions called by <code>foo</code>. Outside of <code>run</code>, calling <code>getStore</code> will return 5971cb0ef41Sopenharmony_ci<code>undefined</code>.</p> 5981cb0ef41Sopenharmony_ci<h4>Troubleshooting: Context loss<span><a class="mark" href="#troubleshooting-context-loss" id="troubleshooting-context-loss">#</a></span><a aria-hidden="true" class="legacy" id="async_context_troubleshooting_context_loss"></a></h4> 5991cb0ef41Sopenharmony_ci<p>In most cases, <code>AsyncLocalStorage</code> works without issues. In rare situations, the 6001cb0ef41Sopenharmony_cicurrent store is lost in one of the asynchronous operations.</p> 6011cb0ef41Sopenharmony_ci<p>If your code is callback-based, it is enough to promisify it with 6021cb0ef41Sopenharmony_ci<a href="util.html#utilpromisifyoriginal"><code>util.promisify()</code></a> so it starts working with native promises.</p> 6031cb0ef41Sopenharmony_ci<p>If you need to use a callback-based API or your code assumes 6041cb0ef41Sopenharmony_cia custom thenable implementation, use the <a href="#class-asyncresource"><code>AsyncResource</code></a> class 6051cb0ef41Sopenharmony_cito associate the asynchronous operation with the correct execution context. 6061cb0ef41Sopenharmony_ciFind the function call responsible for the context loss by logging the content 6071cb0ef41Sopenharmony_ciof <code>asyncLocalStorage.getStore()</code> after the calls you suspect are responsible 6081cb0ef41Sopenharmony_cifor the loss. When the code logs <code>undefined</code>, the last callback called is 6091cb0ef41Sopenharmony_ciprobably responsible for the context loss.</p> 6101cb0ef41Sopenharmony_ci</section><section><h3>Class: <code>AsyncResource</code><span><a class="mark" href="#class-asyncresource" id="class-asyncresource">#</a></span><a aria-hidden="true" class="legacy" id="async_context_class_asyncresource"></a></h3> 6111cb0ef41Sopenharmony_ci<div class="api_metadata"> 6121cb0ef41Sopenharmony_ci<details class="changelog"><summary>History</summary> 6131cb0ef41Sopenharmony_ci<table> 6141cb0ef41Sopenharmony_ci<tbody><tr><th>Version</th><th>Changes</th></tr> 6151cb0ef41Sopenharmony_ci<tr><td>v16.4.0</td> 6161cb0ef41Sopenharmony_ci<td><p>AsyncResource is now Stable. Previously, it had been Experimental.</p></td></tr> 6171cb0ef41Sopenharmony_ci</tbody></table> 6181cb0ef41Sopenharmony_ci</details> 6191cb0ef41Sopenharmony_ci</div> 6201cb0ef41Sopenharmony_ci<p>The class <code>AsyncResource</code> is designed to be extended by the embedder's async 6211cb0ef41Sopenharmony_ciresources. Using this, users can easily trigger the lifetime events of their 6221cb0ef41Sopenharmony_ciown resources.</p> 6231cb0ef41Sopenharmony_ci<p>The <code>init</code> hook will trigger when an <code>AsyncResource</code> is instantiated.</p> 6241cb0ef41Sopenharmony_ci<p>The following is an overview of the <code>AsyncResource</code> API.</p> 6251cb0ef41Sopenharmony_ci 6261cb0ef41Sopenharmony_ci<pre class="with-72-chars"><input class="js-flavor-selector" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> { <span class="hljs-title class_">AsyncResource</span>, executionAsyncId } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:async_hooks'</span>; 6271cb0ef41Sopenharmony_ci 6281cb0ef41Sopenharmony_ci<span class="hljs-comment">// AsyncResource() is meant to be extended. Instantiating a</span> 6291cb0ef41Sopenharmony_ci<span class="hljs-comment">// new AsyncResource() also triggers init. If triggerAsyncId is omitted then</span> 6301cb0ef41Sopenharmony_ci<span class="hljs-comment">// async_hook.executionAsyncId() is used.</span> 6311cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> asyncResource = <span class="hljs-keyword">new</span> <span class="hljs-title class_">AsyncResource</span>( 6321cb0ef41Sopenharmony_ci type, { <span class="hljs-attr">triggerAsyncId</span>: <span class="hljs-title function_">executionAsyncId</span>(), <span class="hljs-attr">requireManualDestroy</span>: <span class="hljs-literal">false</span> }, 6331cb0ef41Sopenharmony_ci); 6341cb0ef41Sopenharmony_ci 6351cb0ef41Sopenharmony_ci<span class="hljs-comment">// Run a function in the execution context of the resource. This will</span> 6361cb0ef41Sopenharmony_ci<span class="hljs-comment">// * establish the context of the resource</span> 6371cb0ef41Sopenharmony_ci<span class="hljs-comment">// * trigger the AsyncHooks before callbacks</span> 6381cb0ef41Sopenharmony_ci<span class="hljs-comment">// * call the provided function `fn` with the supplied arguments</span> 6391cb0ef41Sopenharmony_ci<span class="hljs-comment">// * trigger the AsyncHooks after callbacks</span> 6401cb0ef41Sopenharmony_ci<span class="hljs-comment">// * restore the original execution context</span> 6411cb0ef41Sopenharmony_ciasyncResource.<span class="hljs-title function_">runInAsyncScope</span>(fn, thisArg, ...args); 6421cb0ef41Sopenharmony_ci 6431cb0ef41Sopenharmony_ci<span class="hljs-comment">// Call AsyncHooks destroy callbacks.</span> 6441cb0ef41Sopenharmony_ciasyncResource.<span class="hljs-title function_">emitDestroy</span>(); 6451cb0ef41Sopenharmony_ci 6461cb0ef41Sopenharmony_ci<span class="hljs-comment">// Return the unique ID assigned to the AsyncResource instance.</span> 6471cb0ef41Sopenharmony_ciasyncResource.<span class="hljs-title function_">asyncId</span>(); 6481cb0ef41Sopenharmony_ci 6491cb0ef41Sopenharmony_ci<span class="hljs-comment">// Return the trigger ID for the AsyncResource instance.</span> 6501cb0ef41Sopenharmony_ciasyncResource.<span class="hljs-title function_">triggerAsyncId</span>();</code><code class="language-js cjs"><span class="hljs-keyword">const</span> { <span class="hljs-title class_">AsyncResource</span>, executionAsyncId } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:async_hooks'</span>); 6511cb0ef41Sopenharmony_ci 6521cb0ef41Sopenharmony_ci<span class="hljs-comment">// AsyncResource() is meant to be extended. Instantiating a</span> 6531cb0ef41Sopenharmony_ci<span class="hljs-comment">// new AsyncResource() also triggers init. If triggerAsyncId is omitted then</span> 6541cb0ef41Sopenharmony_ci<span class="hljs-comment">// async_hook.executionAsyncId() is used.</span> 6551cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> asyncResource = <span class="hljs-keyword">new</span> <span class="hljs-title class_">AsyncResource</span>( 6561cb0ef41Sopenharmony_ci type, { <span class="hljs-attr">triggerAsyncId</span>: <span class="hljs-title function_">executionAsyncId</span>(), <span class="hljs-attr">requireManualDestroy</span>: <span class="hljs-literal">false</span> }, 6571cb0ef41Sopenharmony_ci); 6581cb0ef41Sopenharmony_ci 6591cb0ef41Sopenharmony_ci<span class="hljs-comment">// Run a function in the execution context of the resource. This will</span> 6601cb0ef41Sopenharmony_ci<span class="hljs-comment">// * establish the context of the resource</span> 6611cb0ef41Sopenharmony_ci<span class="hljs-comment">// * trigger the AsyncHooks before callbacks</span> 6621cb0ef41Sopenharmony_ci<span class="hljs-comment">// * call the provided function `fn` with the supplied arguments</span> 6631cb0ef41Sopenharmony_ci<span class="hljs-comment">// * trigger the AsyncHooks after callbacks</span> 6641cb0ef41Sopenharmony_ci<span class="hljs-comment">// * restore the original execution context</span> 6651cb0ef41Sopenharmony_ciasyncResource.<span class="hljs-title function_">runInAsyncScope</span>(fn, thisArg, ...args); 6661cb0ef41Sopenharmony_ci 6671cb0ef41Sopenharmony_ci<span class="hljs-comment">// Call AsyncHooks destroy callbacks.</span> 6681cb0ef41Sopenharmony_ciasyncResource.<span class="hljs-title function_">emitDestroy</span>(); 6691cb0ef41Sopenharmony_ci 6701cb0ef41Sopenharmony_ci<span class="hljs-comment">// Return the unique ID assigned to the AsyncResource instance.</span> 6711cb0ef41Sopenharmony_ciasyncResource.<span class="hljs-title function_">asyncId</span>(); 6721cb0ef41Sopenharmony_ci 6731cb0ef41Sopenharmony_ci<span class="hljs-comment">// Return the trigger ID for the AsyncResource instance.</span> 6741cb0ef41Sopenharmony_ciasyncResource.<span class="hljs-title function_">triggerAsyncId</span>();</code><button class="copy-button">copy</button></pre> 6751cb0ef41Sopenharmony_ci<h4><code>new AsyncResource(type[, options])</code><span><a class="mark" href="#new-asyncresourcetype-options" id="new-asyncresourcetype-options">#</a></span><a aria-hidden="true" class="legacy" id="async_context_new_asyncresource_type_options"></a></h4> 6761cb0ef41Sopenharmony_ci<ul> 6771cb0ef41Sopenharmony_ci<li><code>type</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> The type of async event.</li> 6781cb0ef41Sopenharmony_ci<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> 6791cb0ef41Sopenharmony_ci<ul> 6801cb0ef41Sopenharmony_ci<li><code>triggerAsyncId</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> The ID of the execution context that created this 6811cb0ef41Sopenharmony_ciasync event. <strong>Default:</strong> <code>executionAsyncId()</code>.</li> 6821cb0ef41Sopenharmony_ci<li><code>requireManualDestroy</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> If set to <code>true</code>, disables <code>emitDestroy</code> 6831cb0ef41Sopenharmony_ciwhen the object is garbage collected. This usually does not need to be set 6841cb0ef41Sopenharmony_ci(even if <code>emitDestroy</code> is called manually), unless the resource's <code>asyncId</code> 6851cb0ef41Sopenharmony_ciis retrieved and the sensitive API's <code>emitDestroy</code> is called with it. 6861cb0ef41Sopenharmony_ciWhen set to <code>false</code>, the <code>emitDestroy</code> call on garbage collection 6871cb0ef41Sopenharmony_ciwill only take place if there is at least one active <code>destroy</code> hook. 6881cb0ef41Sopenharmony_ci<strong>Default:</strong> <code>false</code>.</li> 6891cb0ef41Sopenharmony_ci</ul> 6901cb0ef41Sopenharmony_ci</li> 6911cb0ef41Sopenharmony_ci</ul> 6921cb0ef41Sopenharmony_ci<p>Example usage:</p> 6931cb0ef41Sopenharmony_ci<pre><code class="language-js"><span class="hljs-keyword">class</span> <span class="hljs-title class_">DBQuery</span> <span class="hljs-keyword">extends</span> <span class="hljs-title class_ inherited__">AsyncResource</span> { 6941cb0ef41Sopenharmony_ci <span class="hljs-title function_">constructor</span>(<span class="hljs-params">db</span>) { 6951cb0ef41Sopenharmony_ci <span class="hljs-variable language_">super</span>(<span class="hljs-string">'DBQuery'</span>); 6961cb0ef41Sopenharmony_ci <span class="hljs-variable language_">this</span>.<span class="hljs-property">db</span> = db; 6971cb0ef41Sopenharmony_ci } 6981cb0ef41Sopenharmony_ci 6991cb0ef41Sopenharmony_ci <span class="hljs-title function_">getInfo</span>(<span class="hljs-params">query, callback</span>) { 7001cb0ef41Sopenharmony_ci <span class="hljs-variable language_">this</span>.<span class="hljs-property">db</span>.<span class="hljs-title function_">get</span>(query, <span class="hljs-function">(<span class="hljs-params">err, data</span>) =></span> { 7011cb0ef41Sopenharmony_ci <span class="hljs-variable language_">this</span>.<span class="hljs-title function_">runInAsyncScope</span>(callback, <span class="hljs-literal">null</span>, err, data); 7021cb0ef41Sopenharmony_ci }); 7031cb0ef41Sopenharmony_ci } 7041cb0ef41Sopenharmony_ci 7051cb0ef41Sopenharmony_ci <span class="hljs-title function_">close</span>(<span class="hljs-params"></span>) { 7061cb0ef41Sopenharmony_ci <span class="hljs-variable language_">this</span>.<span class="hljs-property">db</span> = <span class="hljs-literal">null</span>; 7071cb0ef41Sopenharmony_ci <span class="hljs-variable language_">this</span>.<span class="hljs-title function_">emitDestroy</span>(); 7081cb0ef41Sopenharmony_ci } 7091cb0ef41Sopenharmony_ci}</code> <button class="copy-button">copy</button></pre> 7101cb0ef41Sopenharmony_ci<h4>Static method: <code>AsyncResource.bind(fn[, type[, thisArg]])</code><span><a class="mark" href="#static-method-asyncresourcebindfn-type-thisarg" id="static-method-asyncresourcebindfn-type-thisarg">#</a></span><a aria-hidden="true" class="legacy" id="async_context_static_method_asyncresource_bind_fn_type_thisarg"></a></h4> 7111cb0ef41Sopenharmony_ci<div class="api_metadata"> 7121cb0ef41Sopenharmony_ci<details class="changelog"><summary>History</summary> 7131cb0ef41Sopenharmony_ci<table> 7141cb0ef41Sopenharmony_ci<tbody><tr><th>Version</th><th>Changes</th></tr> 7151cb0ef41Sopenharmony_ci<tr><td>v17.8.0</td> 7161cb0ef41Sopenharmony_ci<td><p>Changed the default when <code>thisArg</code> is undefined to use <code>this</code> from the caller.</p></td></tr> 7171cb0ef41Sopenharmony_ci<tr><td>v16.0.0</td> 7181cb0ef41Sopenharmony_ci<td><p>Added optional thisArg.</p></td></tr> 7191cb0ef41Sopenharmony_ci<tr><td>v14.8.0, v12.19.0</td> 7201cb0ef41Sopenharmony_ci<td><p><span>Added in: v14.8.0, v12.19.0</span></p></td></tr> 7211cb0ef41Sopenharmony_ci</tbody></table> 7221cb0ef41Sopenharmony_ci</details> 7231cb0ef41Sopenharmony_ci</div> 7241cb0ef41Sopenharmony_ci<ul> 7251cb0ef41Sopenharmony_ci<li><code>fn</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> The function to bind to the current execution context.</li> 7261cb0ef41Sopenharmony_ci<li><code>type</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> An optional name to associate with the underlying 7271cb0ef41Sopenharmony_ci<code>AsyncResource</code>.</li> 7281cb0ef41Sopenharmony_ci<li><code>thisArg</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> 7291cb0ef41Sopenharmony_ci</ul> 7301cb0ef41Sopenharmony_ci<p>Binds the given function to the current execution context.</p> 7311cb0ef41Sopenharmony_ci<p>The returned function will have an <code>asyncResource</code> property referencing 7321cb0ef41Sopenharmony_cithe <code>AsyncResource</code> to which the function is bound.</p> 7331cb0ef41Sopenharmony_ci<h4><code>asyncResource.bind(fn[, thisArg])</code><span><a class="mark" href="#asyncresourcebindfn-thisarg" id="asyncresourcebindfn-thisarg">#</a></span><a aria-hidden="true" class="legacy" id="async_context_asyncresource_bind_fn_thisarg"></a></h4> 7341cb0ef41Sopenharmony_ci<div class="api_metadata"> 7351cb0ef41Sopenharmony_ci<details class="changelog"><summary>History</summary> 7361cb0ef41Sopenharmony_ci<table> 7371cb0ef41Sopenharmony_ci<tbody><tr><th>Version</th><th>Changes</th></tr> 7381cb0ef41Sopenharmony_ci<tr><td>v17.8.0</td> 7391cb0ef41Sopenharmony_ci<td><p>Changed the default when <code>thisArg</code> is undefined to use <code>this</code> from the caller.</p></td></tr> 7401cb0ef41Sopenharmony_ci<tr><td>v16.0.0</td> 7411cb0ef41Sopenharmony_ci<td><p>Added optional thisArg.</p></td></tr> 7421cb0ef41Sopenharmony_ci<tr><td>v14.8.0, v12.19.0</td> 7431cb0ef41Sopenharmony_ci<td><p><span>Added in: v14.8.0, v12.19.0</span></p></td></tr> 7441cb0ef41Sopenharmony_ci</tbody></table> 7451cb0ef41Sopenharmony_ci</details> 7461cb0ef41Sopenharmony_ci</div> 7471cb0ef41Sopenharmony_ci<ul> 7481cb0ef41Sopenharmony_ci<li><code>fn</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> The function to bind to the current <code>AsyncResource</code>.</li> 7491cb0ef41Sopenharmony_ci<li><code>thisArg</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li> 7501cb0ef41Sopenharmony_ci</ul> 7511cb0ef41Sopenharmony_ci<p>Binds the given function to execute to this <code>AsyncResource</code>'s scope.</p> 7521cb0ef41Sopenharmony_ci<p>The returned function will have an <code>asyncResource</code> property referencing 7531cb0ef41Sopenharmony_cithe <code>AsyncResource</code> to which the function is bound.</p> 7541cb0ef41Sopenharmony_ci<h4><code>asyncResource.runInAsyncScope(fn[, thisArg, ...args])</code><span><a class="mark" href="#asyncresourceruninasyncscopefn-thisarg-args" id="asyncresourceruninasyncscopefn-thisarg-args">#</a></span><a aria-hidden="true" class="legacy" id="async_context_asyncresource_runinasyncscope_fn_thisarg_args"></a></h4> 7551cb0ef41Sopenharmony_ci<div class="api_metadata"> 7561cb0ef41Sopenharmony_ci<span>Added in: v9.6.0</span> 7571cb0ef41Sopenharmony_ci</div> 7581cb0ef41Sopenharmony_ci<ul> 7591cb0ef41Sopenharmony_ci<li><code>fn</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> The function to call in the execution context of this async 7601cb0ef41Sopenharmony_ciresource.</li> 7611cb0ef41Sopenharmony_ci<li><code>thisArg</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a> The receiver to be used for the function call.</li> 7621cb0ef41Sopenharmony_ci<li><code>...args</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a> Optional arguments to pass to the function.</li> 7631cb0ef41Sopenharmony_ci</ul> 7641cb0ef41Sopenharmony_ci<p>Call the provided function with the provided arguments in the execution context 7651cb0ef41Sopenharmony_ciof the async resource. This will establish the context, trigger the AsyncHooks 7661cb0ef41Sopenharmony_cibefore callbacks, call the function, trigger the AsyncHooks after callbacks, and 7671cb0ef41Sopenharmony_cithen restore the original execution context.</p> 7681cb0ef41Sopenharmony_ci<h4><code>asyncResource.emitDestroy()</code><span><a class="mark" href="#asyncresourceemitdestroy" id="asyncresourceemitdestroy">#</a></span><a aria-hidden="true" class="legacy" id="async_context_asyncresource_emitdestroy"></a></h4> 7691cb0ef41Sopenharmony_ci<ul> 7701cb0ef41Sopenharmony_ci<li>Returns: <a href="async_hooks.html#class-asyncresource" class="type"><AsyncResource></a> A reference to <code>asyncResource</code>.</li> 7711cb0ef41Sopenharmony_ci</ul> 7721cb0ef41Sopenharmony_ci<p>Call all <code>destroy</code> hooks. This should only ever be called once. An error will 7731cb0ef41Sopenharmony_cibe thrown if it is called more than once. This <strong>must</strong> be manually called. If 7741cb0ef41Sopenharmony_cithe resource is left to be collected by the GC then the <code>destroy</code> hooks will 7751cb0ef41Sopenharmony_cinever be called.</p> 7761cb0ef41Sopenharmony_ci<h4><code>asyncResource.asyncId()</code><span><a class="mark" href="#asyncresourceasyncid" id="asyncresourceasyncid">#</a></span><a aria-hidden="true" class="legacy" id="async_context_asyncresource_asyncid"></a></h4> 7771cb0ef41Sopenharmony_ci<ul> 7781cb0ef41Sopenharmony_ci<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> The unique <code>asyncId</code> assigned to the resource.</li> 7791cb0ef41Sopenharmony_ci</ul> 7801cb0ef41Sopenharmony_ci<h4><code>asyncResource.triggerAsyncId()</code><span><a class="mark" href="#asyncresourcetriggerasyncid" id="asyncresourcetriggerasyncid">#</a></span><a aria-hidden="true" class="legacy" id="async_context_asyncresource_triggerasyncid"></a></h4> 7811cb0ef41Sopenharmony_ci<ul> 7821cb0ef41Sopenharmony_ci<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> The same <code>triggerAsyncId</code> that is passed to the 7831cb0ef41Sopenharmony_ci<code>AsyncResource</code> constructor.</li> 7841cb0ef41Sopenharmony_ci</ul> 7851cb0ef41Sopenharmony_ci<p><a id="async-resource-worker-pool"></a></p> 7861cb0ef41Sopenharmony_ci<h4>Using <code>AsyncResource</code> for a <code>Worker</code> thread pool<span><a class="mark" href="#using-asyncresource-for-a-worker-thread-pool" id="using-asyncresource-for-a-worker-thread-pool">#</a></span><a aria-hidden="true" class="legacy" id="async_context_using_asyncresource_for_a_worker_thread_pool"></a></h4> 7871cb0ef41Sopenharmony_ci<p>The following example shows how to use the <code>AsyncResource</code> class to properly 7881cb0ef41Sopenharmony_ciprovide async tracking for a <a href="worker_threads.html#class-worker"><code>Worker</code></a> pool. Other resource pools, such as 7891cb0ef41Sopenharmony_cidatabase connection pools, can follow a similar model.</p> 7901cb0ef41Sopenharmony_ci<p>Assuming that the task is adding two numbers, using a file named 7911cb0ef41Sopenharmony_ci<code>task_processor.js</code> with the following content:</p> 7921cb0ef41Sopenharmony_ci 7931cb0ef41Sopenharmony_ci<pre class="with-54-chars"><input class="js-flavor-selector" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> { parentPort } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:worker_threads'</span>; 7941cb0ef41Sopenharmony_ciparentPort.<span class="hljs-title function_">on</span>(<span class="hljs-string">'message'</span>, <span class="hljs-function">(<span class="hljs-params">task</span>) =></span> { 7951cb0ef41Sopenharmony_ci parentPort.<span class="hljs-title function_">postMessage</span>(task.<span class="hljs-property">a</span> + task.<span class="hljs-property">b</span>); 7961cb0ef41Sopenharmony_ci});</code><code class="language-js cjs"><span class="hljs-keyword">const</span> { parentPort } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:worker_threads'</span>); 7971cb0ef41Sopenharmony_ciparentPort.<span class="hljs-title function_">on</span>(<span class="hljs-string">'message'</span>, <span class="hljs-function">(<span class="hljs-params">task</span>) =></span> { 7981cb0ef41Sopenharmony_ci parentPort.<span class="hljs-title function_">postMessage</span>(task.<span class="hljs-property">a</span> + task.<span class="hljs-property">b</span>); 7991cb0ef41Sopenharmony_ci});</code><button class="copy-button">copy</button></pre> 8001cb0ef41Sopenharmony_ci<p>a Worker pool around it could use the following structure:</p> 8011cb0ef41Sopenharmony_ci 8021cb0ef41Sopenharmony_ci<pre class="with-54-chars"><input class="js-flavor-selector" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> { <span class="hljs-title class_">AsyncResource</span> } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:async_hooks'</span>; 8031cb0ef41Sopenharmony_ci<span class="hljs-keyword">import</span> { <span class="hljs-title class_">EventEmitter</span> } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:events'</span>; 8041cb0ef41Sopenharmony_ci<span class="hljs-keyword">import</span> path <span class="hljs-keyword">from</span> <span class="hljs-string">'node:path'</span>; 8051cb0ef41Sopenharmony_ci<span class="hljs-keyword">import</span> { <span class="hljs-title class_">Worker</span> } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:worker_threads'</span>; 8061cb0ef41Sopenharmony_ci 8071cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> kTaskInfo = <span class="hljs-title class_">Symbol</span>(<span class="hljs-string">'kTaskInfo'</span>); 8081cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> kWorkerFreedEvent = <span class="hljs-title class_">Symbol</span>(<span class="hljs-string">'kWorkerFreedEvent'</span>); 8091cb0ef41Sopenharmony_ci 8101cb0ef41Sopenharmony_ci<span class="hljs-keyword">class</span> <span class="hljs-title class_">WorkerPoolTaskInfo</span> <span class="hljs-keyword">extends</span> <span class="hljs-title class_ inherited__">AsyncResource</span> { 8111cb0ef41Sopenharmony_ci <span class="hljs-title function_">constructor</span>(<span class="hljs-params">callback</span>) { 8121cb0ef41Sopenharmony_ci <span class="hljs-variable language_">super</span>(<span class="hljs-string">'WorkerPoolTaskInfo'</span>); 8131cb0ef41Sopenharmony_ci <span class="hljs-variable language_">this</span>.<span class="hljs-property">callback</span> = callback; 8141cb0ef41Sopenharmony_ci } 8151cb0ef41Sopenharmony_ci 8161cb0ef41Sopenharmony_ci <span class="hljs-title function_">done</span>(<span class="hljs-params">err, result</span>) { 8171cb0ef41Sopenharmony_ci <span class="hljs-variable language_">this</span>.<span class="hljs-title function_">runInAsyncScope</span>(<span class="hljs-variable language_">this</span>.<span class="hljs-property">callback</span>, <span class="hljs-literal">null</span>, err, result); 8181cb0ef41Sopenharmony_ci <span class="hljs-variable language_">this</span>.<span class="hljs-title function_">emitDestroy</span>(); <span class="hljs-comment">// `TaskInfo`s are used only once.</span> 8191cb0ef41Sopenharmony_ci } 8201cb0ef41Sopenharmony_ci} 8211cb0ef41Sopenharmony_ci 8221cb0ef41Sopenharmony_ci<span class="hljs-keyword">export</span> <span class="hljs-keyword">default</span> <span class="hljs-keyword">class</span> <span class="hljs-title class_">WorkerPool</span> <span class="hljs-keyword">extends</span> <span class="hljs-title class_ inherited__">EventEmitter</span> { 8231cb0ef41Sopenharmony_ci <span class="hljs-title function_">constructor</span>(<span class="hljs-params">numThreads</span>) { 8241cb0ef41Sopenharmony_ci <span class="hljs-variable language_">super</span>(); 8251cb0ef41Sopenharmony_ci <span class="hljs-variable language_">this</span>.<span class="hljs-property">numThreads</span> = numThreads; 8261cb0ef41Sopenharmony_ci <span class="hljs-variable language_">this</span>.<span class="hljs-property">workers</span> = []; 8271cb0ef41Sopenharmony_ci <span class="hljs-variable language_">this</span>.<span class="hljs-property">freeWorkers</span> = []; 8281cb0ef41Sopenharmony_ci <span class="hljs-variable language_">this</span>.<span class="hljs-property">tasks</span> = []; 8291cb0ef41Sopenharmony_ci 8301cb0ef41Sopenharmony_ci <span class="hljs-keyword">for</span> (<span class="hljs-keyword">let</span> i = <span class="hljs-number">0</span>; i < numThreads; i++) 8311cb0ef41Sopenharmony_ci <span class="hljs-variable language_">this</span>.<span class="hljs-title function_">addNewWorker</span>(); 8321cb0ef41Sopenharmony_ci 8331cb0ef41Sopenharmony_ci <span class="hljs-comment">// Any time the kWorkerFreedEvent is emitted, dispatch</span> 8341cb0ef41Sopenharmony_ci <span class="hljs-comment">// the next task pending in the queue, if any.</span> 8351cb0ef41Sopenharmony_ci <span class="hljs-variable language_">this</span>.<span class="hljs-title function_">on</span>(kWorkerFreedEvent, <span class="hljs-function">() =></span> { 8361cb0ef41Sopenharmony_ci <span class="hljs-keyword">if</span> (<span class="hljs-variable language_">this</span>.<span class="hljs-property">tasks</span>.<span class="hljs-property">length</span> > <span class="hljs-number">0</span>) { 8371cb0ef41Sopenharmony_ci <span class="hljs-keyword">const</span> { task, callback } = <span class="hljs-variable language_">this</span>.<span class="hljs-property">tasks</span>.<span class="hljs-title function_">shift</span>(); 8381cb0ef41Sopenharmony_ci <span class="hljs-variable language_">this</span>.<span class="hljs-title function_">runTask</span>(task, callback); 8391cb0ef41Sopenharmony_ci } 8401cb0ef41Sopenharmony_ci }); 8411cb0ef41Sopenharmony_ci } 8421cb0ef41Sopenharmony_ci 8431cb0ef41Sopenharmony_ci <span class="hljs-title function_">addNewWorker</span>(<span class="hljs-params"></span>) { 8441cb0ef41Sopenharmony_ci <span class="hljs-keyword">const</span> worker = <span class="hljs-keyword">new</span> <span class="hljs-title class_">Worker</span>(<span class="hljs-keyword">new</span> <span class="hljs-title function_">URL</span>(<span class="hljs-string">'task_processor.js'</span>, <span class="hljs-keyword">import</span>.<span class="hljs-property">meta</span>.<span class="hljs-property">url</span>)); 8451cb0ef41Sopenharmony_ci worker.<span class="hljs-title function_">on</span>(<span class="hljs-string">'message'</span>, <span class="hljs-function">(<span class="hljs-params">result</span>) =></span> { 8461cb0ef41Sopenharmony_ci <span class="hljs-comment">// In case of success: Call the callback that was passed to `runTask`,</span> 8471cb0ef41Sopenharmony_ci <span class="hljs-comment">// remove the `TaskInfo` associated with the Worker, and mark it as free</span> 8481cb0ef41Sopenharmony_ci <span class="hljs-comment">// again.</span> 8491cb0ef41Sopenharmony_ci worker[kTaskInfo].<span class="hljs-title function_">done</span>(<span class="hljs-literal">null</span>, result); 8501cb0ef41Sopenharmony_ci worker[kTaskInfo] = <span class="hljs-literal">null</span>; 8511cb0ef41Sopenharmony_ci <span class="hljs-variable language_">this</span>.<span class="hljs-property">freeWorkers</span>.<span class="hljs-title function_">push</span>(worker); 8521cb0ef41Sopenharmony_ci <span class="hljs-variable language_">this</span>.<span class="hljs-title function_">emit</span>(kWorkerFreedEvent); 8531cb0ef41Sopenharmony_ci }); 8541cb0ef41Sopenharmony_ci worker.<span class="hljs-title function_">on</span>(<span class="hljs-string">'error'</span>, <span class="hljs-function">(<span class="hljs-params">err</span>) =></span> { 8551cb0ef41Sopenharmony_ci <span class="hljs-comment">// In case of an uncaught exception: Call the callback that was passed to</span> 8561cb0ef41Sopenharmony_ci <span class="hljs-comment">// `runTask` with the error.</span> 8571cb0ef41Sopenharmony_ci <span class="hljs-keyword">if</span> (worker[kTaskInfo]) 8581cb0ef41Sopenharmony_ci worker[kTaskInfo].<span class="hljs-title function_">done</span>(err, <span class="hljs-literal">null</span>); 8591cb0ef41Sopenharmony_ci <span class="hljs-keyword">else</span> 8601cb0ef41Sopenharmony_ci <span class="hljs-variable language_">this</span>.<span class="hljs-title function_">emit</span>(<span class="hljs-string">'error'</span>, err); 8611cb0ef41Sopenharmony_ci <span class="hljs-comment">// Remove the worker from the list and start a new Worker to replace the</span> 8621cb0ef41Sopenharmony_ci <span class="hljs-comment">// current one.</span> 8631cb0ef41Sopenharmony_ci <span class="hljs-variable language_">this</span>.<span class="hljs-property">workers</span>.<span class="hljs-title function_">splice</span>(<span class="hljs-variable language_">this</span>.<span class="hljs-property">workers</span>.<span class="hljs-title function_">indexOf</span>(worker), <span class="hljs-number">1</span>); 8641cb0ef41Sopenharmony_ci <span class="hljs-variable language_">this</span>.<span class="hljs-title function_">addNewWorker</span>(); 8651cb0ef41Sopenharmony_ci }); 8661cb0ef41Sopenharmony_ci <span class="hljs-variable language_">this</span>.<span class="hljs-property">workers</span>.<span class="hljs-title function_">push</span>(worker); 8671cb0ef41Sopenharmony_ci <span class="hljs-variable language_">this</span>.<span class="hljs-property">freeWorkers</span>.<span class="hljs-title function_">push</span>(worker); 8681cb0ef41Sopenharmony_ci <span class="hljs-variable language_">this</span>.<span class="hljs-title function_">emit</span>(kWorkerFreedEvent); 8691cb0ef41Sopenharmony_ci } 8701cb0ef41Sopenharmony_ci 8711cb0ef41Sopenharmony_ci <span class="hljs-title function_">runTask</span>(<span class="hljs-params">task, callback</span>) { 8721cb0ef41Sopenharmony_ci <span class="hljs-keyword">if</span> (<span class="hljs-variable language_">this</span>.<span class="hljs-property">freeWorkers</span>.<span class="hljs-property">length</span> === <span class="hljs-number">0</span>) { 8731cb0ef41Sopenharmony_ci <span class="hljs-comment">// No free threads, wait until a worker thread becomes free.</span> 8741cb0ef41Sopenharmony_ci <span class="hljs-variable language_">this</span>.<span class="hljs-property">tasks</span>.<span class="hljs-title function_">push</span>({ task, callback }); 8751cb0ef41Sopenharmony_ci <span class="hljs-keyword">return</span>; 8761cb0ef41Sopenharmony_ci } 8771cb0ef41Sopenharmony_ci 8781cb0ef41Sopenharmony_ci <span class="hljs-keyword">const</span> worker = <span class="hljs-variable language_">this</span>.<span class="hljs-property">freeWorkers</span>.<span class="hljs-title function_">pop</span>(); 8791cb0ef41Sopenharmony_ci worker[kTaskInfo] = <span class="hljs-keyword">new</span> <span class="hljs-title class_">WorkerPoolTaskInfo</span>(callback); 8801cb0ef41Sopenharmony_ci worker.<span class="hljs-title function_">postMessage</span>(task); 8811cb0ef41Sopenharmony_ci } 8821cb0ef41Sopenharmony_ci 8831cb0ef41Sopenharmony_ci <span class="hljs-title function_">close</span>(<span class="hljs-params"></span>) { 8841cb0ef41Sopenharmony_ci <span class="hljs-keyword">for</span> (<span class="hljs-keyword">const</span> worker <span class="hljs-keyword">of</span> <span class="hljs-variable language_">this</span>.<span class="hljs-property">workers</span>) worker.<span class="hljs-title function_">terminate</span>(); 8851cb0ef41Sopenharmony_ci } 8861cb0ef41Sopenharmony_ci}</code><code class="language-js cjs"><span class="hljs-keyword">const</span> { <span class="hljs-title class_">AsyncResource</span> } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:async_hooks'</span>); 8871cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> { <span class="hljs-title class_">EventEmitter</span> } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:events'</span>); 8881cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> path = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:path'</span>); 8891cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> { <span class="hljs-title class_">Worker</span> } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:worker_threads'</span>); 8901cb0ef41Sopenharmony_ci 8911cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> kTaskInfo = <span class="hljs-title class_">Symbol</span>(<span class="hljs-string">'kTaskInfo'</span>); 8921cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> kWorkerFreedEvent = <span class="hljs-title class_">Symbol</span>(<span class="hljs-string">'kWorkerFreedEvent'</span>); 8931cb0ef41Sopenharmony_ci 8941cb0ef41Sopenharmony_ci<span class="hljs-keyword">class</span> <span class="hljs-title class_">WorkerPoolTaskInfo</span> <span class="hljs-keyword">extends</span> <span class="hljs-title class_ inherited__">AsyncResource</span> { 8951cb0ef41Sopenharmony_ci <span class="hljs-title function_">constructor</span>(<span class="hljs-params">callback</span>) { 8961cb0ef41Sopenharmony_ci <span class="hljs-variable language_">super</span>(<span class="hljs-string">'WorkerPoolTaskInfo'</span>); 8971cb0ef41Sopenharmony_ci <span class="hljs-variable language_">this</span>.<span class="hljs-property">callback</span> = callback; 8981cb0ef41Sopenharmony_ci } 8991cb0ef41Sopenharmony_ci 9001cb0ef41Sopenharmony_ci <span class="hljs-title function_">done</span>(<span class="hljs-params">err, result</span>) { 9011cb0ef41Sopenharmony_ci <span class="hljs-variable language_">this</span>.<span class="hljs-title function_">runInAsyncScope</span>(<span class="hljs-variable language_">this</span>.<span class="hljs-property">callback</span>, <span class="hljs-literal">null</span>, err, result); 9021cb0ef41Sopenharmony_ci <span class="hljs-variable language_">this</span>.<span class="hljs-title function_">emitDestroy</span>(); <span class="hljs-comment">// `TaskInfo`s are used only once.</span> 9031cb0ef41Sopenharmony_ci } 9041cb0ef41Sopenharmony_ci} 9051cb0ef41Sopenharmony_ci 9061cb0ef41Sopenharmony_ci<span class="hljs-keyword">class</span> <span class="hljs-title class_">WorkerPool</span> <span class="hljs-keyword">extends</span> <span class="hljs-title class_ inherited__">EventEmitter</span> { 9071cb0ef41Sopenharmony_ci <span class="hljs-title function_">constructor</span>(<span class="hljs-params">numThreads</span>) { 9081cb0ef41Sopenharmony_ci <span class="hljs-variable language_">super</span>(); 9091cb0ef41Sopenharmony_ci <span class="hljs-variable language_">this</span>.<span class="hljs-property">numThreads</span> = numThreads; 9101cb0ef41Sopenharmony_ci <span class="hljs-variable language_">this</span>.<span class="hljs-property">workers</span> = []; 9111cb0ef41Sopenharmony_ci <span class="hljs-variable language_">this</span>.<span class="hljs-property">freeWorkers</span> = []; 9121cb0ef41Sopenharmony_ci <span class="hljs-variable language_">this</span>.<span class="hljs-property">tasks</span> = []; 9131cb0ef41Sopenharmony_ci 9141cb0ef41Sopenharmony_ci <span class="hljs-keyword">for</span> (<span class="hljs-keyword">let</span> i = <span class="hljs-number">0</span>; i < numThreads; i++) 9151cb0ef41Sopenharmony_ci <span class="hljs-variable language_">this</span>.<span class="hljs-title function_">addNewWorker</span>(); 9161cb0ef41Sopenharmony_ci 9171cb0ef41Sopenharmony_ci <span class="hljs-comment">// Any time the kWorkerFreedEvent is emitted, dispatch</span> 9181cb0ef41Sopenharmony_ci <span class="hljs-comment">// the next task pending in the queue, if any.</span> 9191cb0ef41Sopenharmony_ci <span class="hljs-variable language_">this</span>.<span class="hljs-title function_">on</span>(kWorkerFreedEvent, <span class="hljs-function">() =></span> { 9201cb0ef41Sopenharmony_ci <span class="hljs-keyword">if</span> (<span class="hljs-variable language_">this</span>.<span class="hljs-property">tasks</span>.<span class="hljs-property">length</span> > <span class="hljs-number">0</span>) { 9211cb0ef41Sopenharmony_ci <span class="hljs-keyword">const</span> { task, callback } = <span class="hljs-variable language_">this</span>.<span class="hljs-property">tasks</span>.<span class="hljs-title function_">shift</span>(); 9221cb0ef41Sopenharmony_ci <span class="hljs-variable language_">this</span>.<span class="hljs-title function_">runTask</span>(task, callback); 9231cb0ef41Sopenharmony_ci } 9241cb0ef41Sopenharmony_ci }); 9251cb0ef41Sopenharmony_ci } 9261cb0ef41Sopenharmony_ci 9271cb0ef41Sopenharmony_ci <span class="hljs-title function_">addNewWorker</span>(<span class="hljs-params"></span>) { 9281cb0ef41Sopenharmony_ci <span class="hljs-keyword">const</span> worker = <span class="hljs-keyword">new</span> <span class="hljs-title class_">Worker</span>(path.<span class="hljs-title function_">resolve</span>(__dirname, <span class="hljs-string">'task_processor.js'</span>)); 9291cb0ef41Sopenharmony_ci worker.<span class="hljs-title function_">on</span>(<span class="hljs-string">'message'</span>, <span class="hljs-function">(<span class="hljs-params">result</span>) =></span> { 9301cb0ef41Sopenharmony_ci <span class="hljs-comment">// In case of success: Call the callback that was passed to `runTask`,</span> 9311cb0ef41Sopenharmony_ci <span class="hljs-comment">// remove the `TaskInfo` associated with the Worker, and mark it as free</span> 9321cb0ef41Sopenharmony_ci <span class="hljs-comment">// again.</span> 9331cb0ef41Sopenharmony_ci worker[kTaskInfo].<span class="hljs-title function_">done</span>(<span class="hljs-literal">null</span>, result); 9341cb0ef41Sopenharmony_ci worker[kTaskInfo] = <span class="hljs-literal">null</span>; 9351cb0ef41Sopenharmony_ci <span class="hljs-variable language_">this</span>.<span class="hljs-property">freeWorkers</span>.<span class="hljs-title function_">push</span>(worker); 9361cb0ef41Sopenharmony_ci <span class="hljs-variable language_">this</span>.<span class="hljs-title function_">emit</span>(kWorkerFreedEvent); 9371cb0ef41Sopenharmony_ci }); 9381cb0ef41Sopenharmony_ci worker.<span class="hljs-title function_">on</span>(<span class="hljs-string">'error'</span>, <span class="hljs-function">(<span class="hljs-params">err</span>) =></span> { 9391cb0ef41Sopenharmony_ci <span class="hljs-comment">// In case of an uncaught exception: Call the callback that was passed to</span> 9401cb0ef41Sopenharmony_ci <span class="hljs-comment">// `runTask` with the error.</span> 9411cb0ef41Sopenharmony_ci <span class="hljs-keyword">if</span> (worker[kTaskInfo]) 9421cb0ef41Sopenharmony_ci worker[kTaskInfo].<span class="hljs-title function_">done</span>(err, <span class="hljs-literal">null</span>); 9431cb0ef41Sopenharmony_ci <span class="hljs-keyword">else</span> 9441cb0ef41Sopenharmony_ci <span class="hljs-variable language_">this</span>.<span class="hljs-title function_">emit</span>(<span class="hljs-string">'error'</span>, err); 9451cb0ef41Sopenharmony_ci <span class="hljs-comment">// Remove the worker from the list and start a new Worker to replace the</span> 9461cb0ef41Sopenharmony_ci <span class="hljs-comment">// current one.</span> 9471cb0ef41Sopenharmony_ci <span class="hljs-variable language_">this</span>.<span class="hljs-property">workers</span>.<span class="hljs-title function_">splice</span>(<span class="hljs-variable language_">this</span>.<span class="hljs-property">workers</span>.<span class="hljs-title function_">indexOf</span>(worker), <span class="hljs-number">1</span>); 9481cb0ef41Sopenharmony_ci <span class="hljs-variable language_">this</span>.<span class="hljs-title function_">addNewWorker</span>(); 9491cb0ef41Sopenharmony_ci }); 9501cb0ef41Sopenharmony_ci <span class="hljs-variable language_">this</span>.<span class="hljs-property">workers</span>.<span class="hljs-title function_">push</span>(worker); 9511cb0ef41Sopenharmony_ci <span class="hljs-variable language_">this</span>.<span class="hljs-property">freeWorkers</span>.<span class="hljs-title function_">push</span>(worker); 9521cb0ef41Sopenharmony_ci <span class="hljs-variable language_">this</span>.<span class="hljs-title function_">emit</span>(kWorkerFreedEvent); 9531cb0ef41Sopenharmony_ci } 9541cb0ef41Sopenharmony_ci 9551cb0ef41Sopenharmony_ci <span class="hljs-title function_">runTask</span>(<span class="hljs-params">task, callback</span>) { 9561cb0ef41Sopenharmony_ci <span class="hljs-keyword">if</span> (<span class="hljs-variable language_">this</span>.<span class="hljs-property">freeWorkers</span>.<span class="hljs-property">length</span> === <span class="hljs-number">0</span>) { 9571cb0ef41Sopenharmony_ci <span class="hljs-comment">// No free threads, wait until a worker thread becomes free.</span> 9581cb0ef41Sopenharmony_ci <span class="hljs-variable language_">this</span>.<span class="hljs-property">tasks</span>.<span class="hljs-title function_">push</span>({ task, callback }); 9591cb0ef41Sopenharmony_ci <span class="hljs-keyword">return</span>; 9601cb0ef41Sopenharmony_ci } 9611cb0ef41Sopenharmony_ci 9621cb0ef41Sopenharmony_ci <span class="hljs-keyword">const</span> worker = <span class="hljs-variable language_">this</span>.<span class="hljs-property">freeWorkers</span>.<span class="hljs-title function_">pop</span>(); 9631cb0ef41Sopenharmony_ci worker[kTaskInfo] = <span class="hljs-keyword">new</span> <span class="hljs-title class_">WorkerPoolTaskInfo</span>(callback); 9641cb0ef41Sopenharmony_ci worker.<span class="hljs-title function_">postMessage</span>(task); 9651cb0ef41Sopenharmony_ci } 9661cb0ef41Sopenharmony_ci 9671cb0ef41Sopenharmony_ci <span class="hljs-title function_">close</span>(<span class="hljs-params"></span>) { 9681cb0ef41Sopenharmony_ci <span class="hljs-keyword">for</span> (<span class="hljs-keyword">const</span> worker <span class="hljs-keyword">of</span> <span class="hljs-variable language_">this</span>.<span class="hljs-property">workers</span>) worker.<span class="hljs-title function_">terminate</span>(); 9691cb0ef41Sopenharmony_ci } 9701cb0ef41Sopenharmony_ci} 9711cb0ef41Sopenharmony_ci 9721cb0ef41Sopenharmony_ci<span class="hljs-variable language_">module</span>.<span class="hljs-property">exports</span> = <span class="hljs-title class_">WorkerPool</span>;</code><button class="copy-button">copy</button></pre> 9731cb0ef41Sopenharmony_ci<p>Without the explicit tracking added by the <code>WorkerPoolTaskInfo</code> objects, 9741cb0ef41Sopenharmony_ciit would appear that the callbacks are associated with the individual <code>Worker</code> 9751cb0ef41Sopenharmony_ciobjects. However, the creation of the <code>Worker</code>s is not associated with the 9761cb0ef41Sopenharmony_cicreation of the tasks and does not provide information about when tasks 9771cb0ef41Sopenharmony_ciwere scheduled.</p> 9781cb0ef41Sopenharmony_ci<p>This pool could be used as follows:</p> 9791cb0ef41Sopenharmony_ci 9801cb0ef41Sopenharmony_ci<pre class="with-47-chars"><input class="js-flavor-selector" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> <span class="hljs-title class_">WorkerPool</span> <span class="hljs-keyword">from</span> <span class="hljs-string">'./worker_pool.js'</span>; 9811cb0ef41Sopenharmony_ci<span class="hljs-keyword">import</span> os <span class="hljs-keyword">from</span> <span class="hljs-string">'node:os'</span>; 9821cb0ef41Sopenharmony_ci 9831cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> pool = <span class="hljs-keyword">new</span> <span class="hljs-title class_">WorkerPool</span>(os.<span class="hljs-title function_">availableParallelism</span>()); 9841cb0ef41Sopenharmony_ci 9851cb0ef41Sopenharmony_ci<span class="hljs-keyword">let</span> finished = <span class="hljs-number">0</span>; 9861cb0ef41Sopenharmony_ci<span class="hljs-keyword">for</span> (<span class="hljs-keyword">let</span> i = <span class="hljs-number">0</span>; i < <span class="hljs-number">10</span>; i++) { 9871cb0ef41Sopenharmony_ci pool.<span class="hljs-title function_">runTask</span>({ <span class="hljs-attr">a</span>: <span class="hljs-number">42</span>, <span class="hljs-attr">b</span>: <span class="hljs-number">100</span> }, <span class="hljs-function">(<span class="hljs-params">err, result</span>) =></span> { 9881cb0ef41Sopenharmony_ci <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(i, err, result); 9891cb0ef41Sopenharmony_ci <span class="hljs-keyword">if</span> (++finished === <span class="hljs-number">10</span>) 9901cb0ef41Sopenharmony_ci pool.<span class="hljs-title function_">close</span>(); 9911cb0ef41Sopenharmony_ci }); 9921cb0ef41Sopenharmony_ci}</code><code class="language-js cjs"><span class="hljs-keyword">const</span> <span class="hljs-title class_">WorkerPool</span> = <span class="hljs-built_in">require</span>(<span class="hljs-string">'./worker_pool.js'</span>); 9931cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> os = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:os'</span>); 9941cb0ef41Sopenharmony_ci 9951cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> pool = <span class="hljs-keyword">new</span> <span class="hljs-title class_">WorkerPool</span>(os.<span class="hljs-title function_">availableParallelism</span>()); 9961cb0ef41Sopenharmony_ci 9971cb0ef41Sopenharmony_ci<span class="hljs-keyword">let</span> finished = <span class="hljs-number">0</span>; 9981cb0ef41Sopenharmony_ci<span class="hljs-keyword">for</span> (<span class="hljs-keyword">let</span> i = <span class="hljs-number">0</span>; i < <span class="hljs-number">10</span>; i++) { 9991cb0ef41Sopenharmony_ci pool.<span class="hljs-title function_">runTask</span>({ <span class="hljs-attr">a</span>: <span class="hljs-number">42</span>, <span class="hljs-attr">b</span>: <span class="hljs-number">100</span> }, <span class="hljs-function">(<span class="hljs-params">err, result</span>) =></span> { 10001cb0ef41Sopenharmony_ci <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(i, err, result); 10011cb0ef41Sopenharmony_ci <span class="hljs-keyword">if</span> (++finished === <span class="hljs-number">10</span>) 10021cb0ef41Sopenharmony_ci pool.<span class="hljs-title function_">close</span>(); 10031cb0ef41Sopenharmony_ci }); 10041cb0ef41Sopenharmony_ci}</code><button class="copy-button">copy</button></pre> 10051cb0ef41Sopenharmony_ci<h4>Integrating <code>AsyncResource</code> with <code>EventEmitter</code><span><a class="mark" href="#integrating-asyncresource-with-eventemitter" id="integrating-asyncresource-with-eventemitter">#</a></span><a aria-hidden="true" class="legacy" id="async_context_integrating_asyncresource_with_eventemitter"></a></h4> 10061cb0ef41Sopenharmony_ci<p>Event listeners triggered by an <a href="events.html#class-eventemitter"><code>EventEmitter</code></a> may be run in a different 10071cb0ef41Sopenharmony_ciexecution context than the one that was active when <code>eventEmitter.on()</code> was 10081cb0ef41Sopenharmony_cicalled.</p> 10091cb0ef41Sopenharmony_ci<p>The following example shows how to use the <code>AsyncResource</code> class to properly 10101cb0ef41Sopenharmony_ciassociate an event listener with the correct execution context. The same 10111cb0ef41Sopenharmony_ciapproach can be applied to a <a href="stream.html#stream"><code>Stream</code></a> or a similar event-driven class.</p> 10121cb0ef41Sopenharmony_ci 10131cb0ef41Sopenharmony_ci<pre class="with-72-chars"><input class="js-flavor-selector" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> { createServer } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:http'</span>; 10141cb0ef41Sopenharmony_ci<span class="hljs-keyword">import</span> { <span class="hljs-title class_">AsyncResource</span>, executionAsyncId } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:async_hooks'</span>; 10151cb0ef41Sopenharmony_ci 10161cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> server = <span class="hljs-title function_">createServer</span>(<span class="hljs-function">(<span class="hljs-params">req, res</span>) =></span> { 10171cb0ef41Sopenharmony_ci req.<span class="hljs-title function_">on</span>(<span class="hljs-string">'close'</span>, <span class="hljs-title class_">AsyncResource</span>.<span class="hljs-title function_">bind</span>(<span class="hljs-function">() =></span> { 10181cb0ef41Sopenharmony_ci <span class="hljs-comment">// Execution context is bound to the current outer scope.</span> 10191cb0ef41Sopenharmony_ci })); 10201cb0ef41Sopenharmony_ci req.<span class="hljs-title function_">on</span>(<span class="hljs-string">'close'</span>, <span class="hljs-function">() =></span> { 10211cb0ef41Sopenharmony_ci <span class="hljs-comment">// Execution context is bound to the scope that caused 'close' to emit.</span> 10221cb0ef41Sopenharmony_ci }); 10231cb0ef41Sopenharmony_ci res.<span class="hljs-title function_">end</span>(); 10241cb0ef41Sopenharmony_ci}).<span class="hljs-title function_">listen</span>(<span class="hljs-number">3000</span>);</code><code class="language-js cjs"><span class="hljs-keyword">const</span> { createServer } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:http'</span>); 10251cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> { <span class="hljs-title class_">AsyncResource</span>, executionAsyncId } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:async_hooks'</span>); 10261cb0ef41Sopenharmony_ci 10271cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> server = <span class="hljs-title function_">createServer</span>(<span class="hljs-function">(<span class="hljs-params">req, res</span>) =></span> { 10281cb0ef41Sopenharmony_ci req.<span class="hljs-title function_">on</span>(<span class="hljs-string">'close'</span>, <span class="hljs-title class_">AsyncResource</span>.<span class="hljs-title function_">bind</span>(<span class="hljs-function">() =></span> { 10291cb0ef41Sopenharmony_ci <span class="hljs-comment">// Execution context is bound to the current outer scope.</span> 10301cb0ef41Sopenharmony_ci })); 10311cb0ef41Sopenharmony_ci req.<span class="hljs-title function_">on</span>(<span class="hljs-string">'close'</span>, <span class="hljs-function">() =></span> { 10321cb0ef41Sopenharmony_ci <span class="hljs-comment">// Execution context is bound to the scope that caused 'close' to emit.</span> 10331cb0ef41Sopenharmony_ci }); 10341cb0ef41Sopenharmony_ci res.<span class="hljs-title function_">end</span>(); 10351cb0ef41Sopenharmony_ci}).<span class="hljs-title function_">listen</span>(<span class="hljs-number">3000</span>);</code><button class="copy-button">copy</button></pre></section> 10361cb0ef41Sopenharmony_ci <!-- API END --> 10371cb0ef41Sopenharmony_ci </div> 10381cb0ef41Sopenharmony_ci </div> 10391cb0ef41Sopenharmony_ci </div> 10401cb0ef41Sopenharmony_ci</body> 10411cb0ef41Sopenharmony_ci</html> 1042