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aria-label="Toggle dark mode/light mode" hidden> 1011cb0ef41Sopenharmony_ci <svg xmlns="http://www.w3.org/2000/svg" class="icon dark-icon" height="24" width="24"> 1021cb0ef41Sopenharmony_ci <path fill="none" d="M0 0h24v24H0z" /> 1031cb0ef41Sopenharmony_ci <path d="M11.1 12.08c-2.33-4.51-.5-8.48.53-10.07C6.27 2.2 1.98 6.59 1.98 12c0 .14.02.28.02.42.62-.27 1.29-.42 2-.42 1.66 0 3.18.83 4.1 2.15A4.01 4.01 0 0111 18c0 1.52-.87 2.83-2.12 3.51.98.32 2.03.5 3.11.5 3.5 0 6.58-1.8 8.37-4.52-2.36.23-6.98-.97-9.26-5.41z"/> 1041cb0ef41Sopenharmony_ci <path d="M7 16h-.18C6.4 14.84 5.3 14 4 14c-1.66 0-3 1.34-3 3s1.34 3 3 3h3c1.1 0 2-.9 2-2s-.9-2-2-2z"/> 1051cb0ef41Sopenharmony_ci </svg> 1061cb0ef41Sopenharmony_ci <svg xmlns="http://www.w3.org/2000/svg" class="icon light-icon" height="24" width="24"> 1071cb0ef41Sopenharmony_ci <path d="M0 0h24v24H0z" fill="none" /> 1081cb0ef41Sopenharmony_ci <path d="M6.76 4.84l-1.8-1.79-1.41 1.41 1.79 1.79 1.42-1.41zM4 10.5H1v2h3v-2zm9-9.95h-2V3.5h2V.55zm7.45 3.91l-1.41-1.41-1.79 1.79 1.41 1.41 1.79-1.79zm-3.21 13.7l1.79 1.8 1.41-1.41-1.8-1.79-1.4 1.4zM20 10.5v2h3v-2h-3zm-8-5c-3.31 0-6 2.69-6 6s2.69 6 6 6 6-2.69 6-6-2.69-6-6-6zm-1 16.95h2V19.5h-2v2.95zm-7.45-3.91l1.41 1.41 1.79-1.8-1.41-1.41-1.79 1.8z"/> 1091cb0ef41Sopenharmony_ci </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_1"><a href="#async-hooks">Async hooks</a></span> 1241cb0ef41Sopenharmony_ci<ul> 1251cb0ef41Sopenharmony_ci<li><a href="#terminology">Terminology</a></li> 1261cb0ef41Sopenharmony_ci<li><a href="#overview">Overview</a></li> 1271cb0ef41Sopenharmony_ci<li><a href="#async_hookscreatehookcallbacks"><code>async_hooks.createHook(callbacks)</code></a> 1281cb0ef41Sopenharmony_ci<ul> 1291cb0ef41Sopenharmony_ci<li><a href="#error-handling">Error handling</a></li> 1301cb0ef41Sopenharmony_ci<li><a href="#printing-in-asynchook-callbacks">Printing in <code>AsyncHook</code> callbacks</a></li> 1311cb0ef41Sopenharmony_ci</ul> 1321cb0ef41Sopenharmony_ci</li> 1331cb0ef41Sopenharmony_ci<li><a href="#class-asynchook">Class: <code>AsyncHook</code></a> 1341cb0ef41Sopenharmony_ci<ul> 1351cb0ef41Sopenharmony_ci<li><a href="#asynchookenable"><code>asyncHook.enable()</code></a></li> 1361cb0ef41Sopenharmony_ci<li><a href="#asynchookdisable"><code>asyncHook.disable()</code></a></li> 1371cb0ef41Sopenharmony_ci<li><a href="#hook-callbacks">Hook callbacks</a> 1381cb0ef41Sopenharmony_ci<ul> 1391cb0ef41Sopenharmony_ci<li><a href="#initasyncid-type-triggerasyncid-resource"><code>init(asyncId, type, triggerAsyncId, resource)</code></a> 1401cb0ef41Sopenharmony_ci<ul> 1411cb0ef41Sopenharmony_ci<li><a href="#type"><code>type</code></a></li> 1421cb0ef41Sopenharmony_ci<li><a href="#triggerasyncid"><code>triggerAsyncId</code></a></li> 1431cb0ef41Sopenharmony_ci<li><a href="#resource"><code>resource</code></a></li> 1441cb0ef41Sopenharmony_ci<li><a href="#asynchronous-context-example">Asynchronous context example</a></li> 1451cb0ef41Sopenharmony_ci</ul> 1461cb0ef41Sopenharmony_ci</li> 1471cb0ef41Sopenharmony_ci<li><a href="#beforeasyncid"><code>before(asyncId)</code></a></li> 1481cb0ef41Sopenharmony_ci<li><a href="#afterasyncid"><code>after(asyncId)</code></a></li> 1491cb0ef41Sopenharmony_ci<li><a href="#destroyasyncid"><code>destroy(asyncId)</code></a></li> 1501cb0ef41Sopenharmony_ci<li><a href="#promiseresolveasyncid"><code>promiseResolve(asyncId)</code></a></li> 1511cb0ef41Sopenharmony_ci</ul> 1521cb0ef41Sopenharmony_ci</li> 1531cb0ef41Sopenharmony_ci<li><a href="#async_hooksexecutionasyncresource"><code>async_hooks.executionAsyncResource()</code></a></li> 1541cb0ef41Sopenharmony_ci<li><a href="#async_hooksexecutionasyncid"><code>async_hooks.executionAsyncId()</code></a></li> 1551cb0ef41Sopenharmony_ci<li><a href="#async_hookstriggerasyncid"><code>async_hooks.triggerAsyncId()</code></a></li> 1561cb0ef41Sopenharmony_ci<li><a href="#async_hooksasyncwrapproviders"><code>async_hooks.asyncWrapProviders</code></a></li> 1571cb0ef41Sopenharmony_ci</ul> 1581cb0ef41Sopenharmony_ci</li> 1591cb0ef41Sopenharmony_ci<li><a href="#promise-execution-tracking">Promise execution tracking</a></li> 1601cb0ef41Sopenharmony_ci<li><a href="#javascript-embedder-api">JavaScript embedder API</a> 1611cb0ef41Sopenharmony_ci<ul> 1621cb0ef41Sopenharmony_ci<li><a href="#class-asyncresource">Class: <code>AsyncResource</code></a></li> 1631cb0ef41Sopenharmony_ci</ul> 1641cb0ef41Sopenharmony_ci</li> 1651cb0ef41Sopenharmony_ci<li><a href="#class-asynclocalstorage">Class: <code>AsyncLocalStorage</code></a></li> 1661cb0ef41Sopenharmony_ci</ul> 1671cb0ef41Sopenharmony_ci</li> 1681cb0ef41Sopenharmony_ci</ul></div></div> 1691cb0ef41Sopenharmony_ci </li> 1701cb0ef41Sopenharmony_ci 1711cb0ef41Sopenharmony_ci 1721cb0ef41Sopenharmony_ci <li class="picker-header"> 1731cb0ef41Sopenharmony_ci <a href="#"> 1741cb0ef41Sopenharmony_ci <span class="collapsed-arrow">►</span><span class="expanded-arrow">▼</span> 1751cb0ef41Sopenharmony_ci Index 1761cb0ef41Sopenharmony_ci </a> 1771cb0ef41Sopenharmony_ci 1781cb0ef41Sopenharmony_ci <div class="picker"><ul> 1791cb0ef41Sopenharmony_ci<li><a href="documentation.html" class="nav-documentation">About this documentation</a></li> 1801cb0ef41Sopenharmony_ci<li><a href="synopsis.html" class="nav-synopsis">Usage and example</a></li> 1811cb0ef41Sopenharmony_ci 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as JSON</a> 2911cb0ef41Sopenharmony_ci </li> 2921cb0ef41Sopenharmony_ci <li class="edit_on_github"><a href="https://github.com/nodejs/node/edit/main/doc/api/async_hooks.md">Edit on GitHub</a></li> 2931cb0ef41Sopenharmony_ci </ul> 2941cb0ef41Sopenharmony_ci </div> 2951cb0ef41Sopenharmony_ci </li> 2961cb0ef41Sopenharmony_ci </ul> 2971cb0ef41Sopenharmony_ci </div> 2981cb0ef41Sopenharmony_ci <hr> 2991cb0ef41Sopenharmony_ci </header> 3001cb0ef41Sopenharmony_ci 3011cb0ef41Sopenharmony_ci <details id="toc" open><summary>Table of contents</summary><ul> 3021cb0ef41Sopenharmony_ci<li><span class="stability_1"><a href="#async-hooks">Async hooks</a></span> 3031cb0ef41Sopenharmony_ci<ul> 3041cb0ef41Sopenharmony_ci<li><a href="#terminology">Terminology</a></li> 3051cb0ef41Sopenharmony_ci<li><a href="#overview">Overview</a></li> 3061cb0ef41Sopenharmony_ci<li><a href="#async_hookscreatehookcallbacks"><code>async_hooks.createHook(callbacks)</code></a> 3071cb0ef41Sopenharmony_ci<ul> 3081cb0ef41Sopenharmony_ci<li><a href="#error-handling">Error handling</a></li> 3091cb0ef41Sopenharmony_ci<li><a href="#printing-in-asynchook-callbacks">Printing in <code>AsyncHook</code> callbacks</a></li> 3101cb0ef41Sopenharmony_ci</ul> 3111cb0ef41Sopenharmony_ci</li> 3121cb0ef41Sopenharmony_ci<li><a href="#class-asynchook">Class: <code>AsyncHook</code></a> 3131cb0ef41Sopenharmony_ci<ul> 3141cb0ef41Sopenharmony_ci<li><a href="#asynchookenable"><code>asyncHook.enable()</code></a></li> 3151cb0ef41Sopenharmony_ci<li><a href="#asynchookdisable"><code>asyncHook.disable()</code></a></li> 3161cb0ef41Sopenharmony_ci<li><a href="#hook-callbacks">Hook callbacks</a> 3171cb0ef41Sopenharmony_ci<ul> 3181cb0ef41Sopenharmony_ci<li><a href="#initasyncid-type-triggerasyncid-resource"><code>init(asyncId, type, triggerAsyncId, resource)</code></a> 3191cb0ef41Sopenharmony_ci<ul> 3201cb0ef41Sopenharmony_ci<li><a href="#type"><code>type</code></a></li> 3211cb0ef41Sopenharmony_ci<li><a href="#triggerasyncid"><code>triggerAsyncId</code></a></li> 3221cb0ef41Sopenharmony_ci<li><a href="#resource"><code>resource</code></a></li> 3231cb0ef41Sopenharmony_ci<li><a href="#asynchronous-context-example">Asynchronous context example</a></li> 3241cb0ef41Sopenharmony_ci</ul> 3251cb0ef41Sopenharmony_ci</li> 3261cb0ef41Sopenharmony_ci<li><a href="#beforeasyncid"><code>before(asyncId)</code></a></li> 3271cb0ef41Sopenharmony_ci<li><a href="#afterasyncid"><code>after(asyncId)</code></a></li> 3281cb0ef41Sopenharmony_ci<li><a href="#destroyasyncid"><code>destroy(asyncId)</code></a></li> 3291cb0ef41Sopenharmony_ci<li><a href="#promiseresolveasyncid"><code>promiseResolve(asyncId)</code></a></li> 3301cb0ef41Sopenharmony_ci</ul> 3311cb0ef41Sopenharmony_ci</li> 3321cb0ef41Sopenharmony_ci<li><a href="#async_hooksexecutionasyncresource"><code>async_hooks.executionAsyncResource()</code></a></li> 3331cb0ef41Sopenharmony_ci<li><a href="#async_hooksexecutionasyncid"><code>async_hooks.executionAsyncId()</code></a></li> 3341cb0ef41Sopenharmony_ci<li><a href="#async_hookstriggerasyncid"><code>async_hooks.triggerAsyncId()</code></a></li> 3351cb0ef41Sopenharmony_ci<li><a href="#async_hooksasyncwrapproviders"><code>async_hooks.asyncWrapProviders</code></a></li> 3361cb0ef41Sopenharmony_ci</ul> 3371cb0ef41Sopenharmony_ci</li> 3381cb0ef41Sopenharmony_ci<li><a href="#promise-execution-tracking">Promise execution tracking</a></li> 3391cb0ef41Sopenharmony_ci<li><a href="#javascript-embedder-api">JavaScript embedder API</a> 3401cb0ef41Sopenharmony_ci<ul> 3411cb0ef41Sopenharmony_ci<li><a href="#class-asyncresource">Class: <code>AsyncResource</code></a></li> 3421cb0ef41Sopenharmony_ci</ul> 3431cb0ef41Sopenharmony_ci</li> 3441cb0ef41Sopenharmony_ci<li><a href="#class-asynclocalstorage">Class: <code>AsyncLocalStorage</code></a></li> 3451cb0ef41Sopenharmony_ci</ul> 3461cb0ef41Sopenharmony_ci</li> 3471cb0ef41Sopenharmony_ci</ul></details> 3481cb0ef41Sopenharmony_ci 3491cb0ef41Sopenharmony_ci <div id="apicontent"> 3501cb0ef41Sopenharmony_ci <h2>Async hooks<span><a class="mark" href="#async-hooks" id="async-hooks">#</a></span><a aria-hidden="true" class="legacy" id="async_hooks_async_hooks"></a></h2> 3511cb0ef41Sopenharmony_ci 3521cb0ef41Sopenharmony_ci<p></p><div class="api_stability api_stability_1"><a href="documentation.html#stability-index">Stability: 1</a> - Experimental. Please migrate away from this API, if you can. 3531cb0ef41Sopenharmony_ciWe do not recommend using the <a href="#async_hookscreatehookcallbacks"><code>createHook</code></a>, <a href="#class-asynchook"><code>AsyncHook</code></a>, and 3541cb0ef41Sopenharmony_ci<a href="#async_hooksexecutionasyncresource"><code>executionAsyncResource</code></a> APIs as they have usability issues, safety risks, 3551cb0ef41Sopenharmony_ciand performance implications. Async context tracking use cases are better 3561cb0ef41Sopenharmony_ciserved by the stable <a href="async_context.html#class-asynclocalstorage"><code>AsyncLocalStorage</code></a> API. If you have a use case for 3571cb0ef41Sopenharmony_ci<code>createHook</code>, <code>AsyncHook</code>, or <code>executionAsyncResource</code> beyond the context 3581cb0ef41Sopenharmony_citracking need solved by <a href="async_context.html#class-asynclocalstorage"><code>AsyncLocalStorage</code></a> or diagnostics data currently 3591cb0ef41Sopenharmony_ciprovided by <a href="diagnostics_channel.html">Diagnostics Channel</a>, please open an issue at 3601cb0ef41Sopenharmony_ci<a href="https://github.com/nodejs/node/issues">https://github.com/nodejs/node/issues</a> describing your use case so we can 3611cb0ef41Sopenharmony_cicreate a more purpose-focused API.</div><p></p> 3621cb0ef41Sopenharmony_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> 3631cb0ef41Sopenharmony_ci<p>We strongly discourage the use of the <code>async_hooks</code> API. 3641cb0ef41Sopenharmony_ciOther APIs that can cover most of its use cases include:</p> 3651cb0ef41Sopenharmony_ci<ul> 3661cb0ef41Sopenharmony_ci<li><a href="async_context.html#class-asynclocalstorage"><code>AsyncLocalStorage</code></a> tracks async context</li> 3671cb0ef41Sopenharmony_ci<li><a href="process.html#processgetactiveresourcesinfo"><code>process.getActiveResourcesInfo()</code></a> tracks active resources</li> 3681cb0ef41Sopenharmony_ci</ul> 3691cb0ef41Sopenharmony_ci<p>The <code>node:async_hooks</code> module provides an API to track asynchronous resources. 3701cb0ef41Sopenharmony_ciIt can be accessed using:</p> 3711cb0ef41Sopenharmony_ci 3721cb0ef41Sopenharmony_ci<pre class="with-48-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> async_hooks <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> async_hooks = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:async_hooks'</span>);</code><button class="copy-button">copy</button></pre> 3731cb0ef41Sopenharmony_ci<section><h3>Terminology<span><a class="mark" href="#terminology" id="terminology">#</a></span><a aria-hidden="true" class="legacy" id="async_hooks_terminology"></a></h3> 3741cb0ef41Sopenharmony_ci<p>An asynchronous resource represents an object with an associated callback. 3751cb0ef41Sopenharmony_ciThis callback may be called multiple times, such as the <code>'connection'</code> 3761cb0ef41Sopenharmony_cievent in <code>net.createServer()</code>, or just a single time like in <code>fs.open()</code>. 3771cb0ef41Sopenharmony_ciA resource can also be closed before the callback is called. <code>AsyncHook</code> does 3781cb0ef41Sopenharmony_cinot explicitly distinguish between these different cases but will represent them 3791cb0ef41Sopenharmony_cias the abstract concept that is a resource.</p> 3801cb0ef41Sopenharmony_ci<p>If <a href="worker_threads.html#class-worker"><code>Worker</code></a>s are used, each thread has an independent <code>async_hooks</code> 3811cb0ef41Sopenharmony_ciinterface, and each thread will use a new set of async IDs.</p> 3821cb0ef41Sopenharmony_ci</section><section><h3>Overview<span><a class="mark" href="#overview" id="overview">#</a></span><a aria-hidden="true" class="legacy" id="async_hooks_overview"></a></h3> 3831cb0ef41Sopenharmony_ci<p>Following is a simple overview of the public API.</p> 3841cb0ef41Sopenharmony_ci 3851cb0ef41Sopenharmony_ci<pre class="with-48-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> async_hooks <span class="hljs-keyword">from</span> <span class="hljs-string">'node:async_hooks'</span>; 3861cb0ef41Sopenharmony_ci 3871cb0ef41Sopenharmony_ci<span class="hljs-comment">// Return the ID of the current execution context.</span> 3881cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> eid = async_hooks.<span class="hljs-title function_">executionAsyncId</span>(); 3891cb0ef41Sopenharmony_ci 3901cb0ef41Sopenharmony_ci<span class="hljs-comment">// Return the ID of the handle responsible for triggering the callback of the</span> 3911cb0ef41Sopenharmony_ci<span class="hljs-comment">// current execution scope to call.</span> 3921cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> tid = async_hooks.<span class="hljs-title function_">triggerAsyncId</span>(); 3931cb0ef41Sopenharmony_ci 3941cb0ef41Sopenharmony_ci<span class="hljs-comment">// Create a new AsyncHook instance. All of these callbacks are optional.</span> 3951cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> asyncHook = 3961cb0ef41Sopenharmony_ci async_hooks.<span class="hljs-title function_">createHook</span>({ init, before, after, destroy, promiseResolve }); 3971cb0ef41Sopenharmony_ci 3981cb0ef41Sopenharmony_ci<span class="hljs-comment">// Allow callbacks of this AsyncHook instance to call. This is not an implicit</span> 3991cb0ef41Sopenharmony_ci<span class="hljs-comment">// action after running the constructor, and must be explicitly run to begin</span> 4001cb0ef41Sopenharmony_ci<span class="hljs-comment">// executing callbacks.</span> 4011cb0ef41Sopenharmony_ciasyncHook.<span class="hljs-title function_">enable</span>(); 4021cb0ef41Sopenharmony_ci 4031cb0ef41Sopenharmony_ci<span class="hljs-comment">// Disable listening for new asynchronous events.</span> 4041cb0ef41Sopenharmony_ciasyncHook.<span class="hljs-title function_">disable</span>(); 4051cb0ef41Sopenharmony_ci 4061cb0ef41Sopenharmony_ci<span class="hljs-comment">//</span> 4071cb0ef41Sopenharmony_ci<span class="hljs-comment">// The following are the callbacks that can be passed to createHook().</span> 4081cb0ef41Sopenharmony_ci<span class="hljs-comment">//</span> 4091cb0ef41Sopenharmony_ci 4101cb0ef41Sopenharmony_ci<span class="hljs-comment">// init() is called during object construction. The resource may not have</span> 4111cb0ef41Sopenharmony_ci<span class="hljs-comment">// completed construction when this callback runs. Therefore, all fields of the</span> 4121cb0ef41Sopenharmony_ci<span class="hljs-comment">// resource referenced by "asyncId" may not have been populated.</span> 4131cb0ef41Sopenharmony_ci<span class="hljs-keyword">function</span> <span class="hljs-title function_">init</span>(<span class="hljs-params">asyncId, type, triggerAsyncId, resource</span>) { } 4141cb0ef41Sopenharmony_ci 4151cb0ef41Sopenharmony_ci<span class="hljs-comment">// before() is called just before the resource's callback is called. It can be</span> 4161cb0ef41Sopenharmony_ci<span class="hljs-comment">// called 0-N times for handles (such as TCPWrap), and will be called exactly 1</span> 4171cb0ef41Sopenharmony_ci<span class="hljs-comment">// time for requests (such as FSReqCallback).</span> 4181cb0ef41Sopenharmony_ci<span class="hljs-keyword">function</span> <span class="hljs-title function_">before</span>(<span class="hljs-params">asyncId</span>) { } 4191cb0ef41Sopenharmony_ci 4201cb0ef41Sopenharmony_ci<span class="hljs-comment">// after() is called just after the resource's callback has finished.</span> 4211cb0ef41Sopenharmony_ci<span class="hljs-keyword">function</span> <span class="hljs-title function_">after</span>(<span class="hljs-params">asyncId</span>) { } 4221cb0ef41Sopenharmony_ci 4231cb0ef41Sopenharmony_ci<span class="hljs-comment">// destroy() is called when the resource is destroyed.</span> 4241cb0ef41Sopenharmony_ci<span class="hljs-keyword">function</span> <span class="hljs-title function_">destroy</span>(<span class="hljs-params">asyncId</span>) { } 4251cb0ef41Sopenharmony_ci 4261cb0ef41Sopenharmony_ci<span class="hljs-comment">// promiseResolve() is called only for promise resources, when the</span> 4271cb0ef41Sopenharmony_ci<span class="hljs-comment">// resolve() function passed to the Promise constructor is invoked</span> 4281cb0ef41Sopenharmony_ci<span class="hljs-comment">// (either directly or through other means of resolving a promise).</span> 4291cb0ef41Sopenharmony_ci<span class="hljs-keyword">function</span> <span class="hljs-title function_">promiseResolve</span>(<span class="hljs-params">asyncId</span>) { }</code><code class="language-js cjs"><span class="hljs-keyword">const</span> async_hooks = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:async_hooks'</span>); 4301cb0ef41Sopenharmony_ci 4311cb0ef41Sopenharmony_ci<span class="hljs-comment">// Return the ID of the current execution context.</span> 4321cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> eid = async_hooks.<span class="hljs-title function_">executionAsyncId</span>(); 4331cb0ef41Sopenharmony_ci 4341cb0ef41Sopenharmony_ci<span class="hljs-comment">// Return the ID of the handle responsible for triggering the callback of the</span> 4351cb0ef41Sopenharmony_ci<span class="hljs-comment">// current execution scope to call.</span> 4361cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> tid = async_hooks.<span class="hljs-title function_">triggerAsyncId</span>(); 4371cb0ef41Sopenharmony_ci 4381cb0ef41Sopenharmony_ci<span class="hljs-comment">// Create a new AsyncHook instance. All of these callbacks are optional.</span> 4391cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> asyncHook = 4401cb0ef41Sopenharmony_ci async_hooks.<span class="hljs-title function_">createHook</span>({ init, before, after, destroy, promiseResolve }); 4411cb0ef41Sopenharmony_ci 4421cb0ef41Sopenharmony_ci<span class="hljs-comment">// Allow callbacks of this AsyncHook instance to call. This is not an implicit</span> 4431cb0ef41Sopenharmony_ci<span class="hljs-comment">// action after running the constructor, and must be explicitly run to begin</span> 4441cb0ef41Sopenharmony_ci<span class="hljs-comment">// executing callbacks.</span> 4451cb0ef41Sopenharmony_ciasyncHook.<span class="hljs-title function_">enable</span>(); 4461cb0ef41Sopenharmony_ci 4471cb0ef41Sopenharmony_ci<span class="hljs-comment">// Disable listening for new asynchronous events.</span> 4481cb0ef41Sopenharmony_ciasyncHook.<span class="hljs-title function_">disable</span>(); 4491cb0ef41Sopenharmony_ci 4501cb0ef41Sopenharmony_ci<span class="hljs-comment">//</span> 4511cb0ef41Sopenharmony_ci<span class="hljs-comment">// The following are the callbacks that can be passed to createHook().</span> 4521cb0ef41Sopenharmony_ci<span class="hljs-comment">//</span> 4531cb0ef41Sopenharmony_ci 4541cb0ef41Sopenharmony_ci<span class="hljs-comment">// init() is called during object construction. The resource may not have</span> 4551cb0ef41Sopenharmony_ci<span class="hljs-comment">// completed construction when this callback runs. Therefore, all fields of the</span> 4561cb0ef41Sopenharmony_ci<span class="hljs-comment">// resource referenced by "asyncId" may not have been populated.</span> 4571cb0ef41Sopenharmony_ci<span class="hljs-keyword">function</span> <span class="hljs-title function_">init</span>(<span class="hljs-params">asyncId, type, triggerAsyncId, resource</span>) { } 4581cb0ef41Sopenharmony_ci 4591cb0ef41Sopenharmony_ci<span class="hljs-comment">// before() is called just before the resource's callback is called. It can be</span> 4601cb0ef41Sopenharmony_ci<span class="hljs-comment">// called 0-N times for handles (such as TCPWrap), and will be called exactly 1</span> 4611cb0ef41Sopenharmony_ci<span class="hljs-comment">// time for requests (such as FSReqCallback).</span> 4621cb0ef41Sopenharmony_ci<span class="hljs-keyword">function</span> <span class="hljs-title function_">before</span>(<span class="hljs-params">asyncId</span>) { } 4631cb0ef41Sopenharmony_ci 4641cb0ef41Sopenharmony_ci<span class="hljs-comment">// after() is called just after the resource's callback has finished.</span> 4651cb0ef41Sopenharmony_ci<span class="hljs-keyword">function</span> <span class="hljs-title function_">after</span>(<span class="hljs-params">asyncId</span>) { } 4661cb0ef41Sopenharmony_ci 4671cb0ef41Sopenharmony_ci<span class="hljs-comment">// destroy() is called when the resource is destroyed.</span> 4681cb0ef41Sopenharmony_ci<span class="hljs-keyword">function</span> <span class="hljs-title function_">destroy</span>(<span class="hljs-params">asyncId</span>) { } 4691cb0ef41Sopenharmony_ci 4701cb0ef41Sopenharmony_ci<span class="hljs-comment">// promiseResolve() is called only for promise resources, when the</span> 4711cb0ef41Sopenharmony_ci<span class="hljs-comment">// resolve() function passed to the Promise constructor is invoked</span> 4721cb0ef41Sopenharmony_ci<span class="hljs-comment">// (either directly or through other means of resolving a promise).</span> 4731cb0ef41Sopenharmony_ci<span class="hljs-keyword">function</span> <span class="hljs-title function_">promiseResolve</span>(<span class="hljs-params">asyncId</span>) { }</code><button class="copy-button">copy</button></pre> 4741cb0ef41Sopenharmony_ci</section><section><h3><code>async_hooks.createHook(callbacks)</code><span><a class="mark" href="#async_hookscreatehookcallbacks" id="async_hookscreatehookcallbacks">#</a></span><a aria-hidden="true" class="legacy" id="async_hooks_async_hooks_createhook_callbacks"></a></h3> 4751cb0ef41Sopenharmony_ci<div class="api_metadata"> 4761cb0ef41Sopenharmony_ci<span>Added in: v8.1.0</span> 4771cb0ef41Sopenharmony_ci</div> 4781cb0ef41Sopenharmony_ci<ul> 4791cb0ef41Sopenharmony_ci<li><code>callbacks</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> The <a href="#hook-callbacks">Hook Callbacks</a> to register 4801cb0ef41Sopenharmony_ci<ul> 4811cb0ef41Sopenharmony_ci<li><code>init</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> The <a href="#initasyncid-type-triggerasyncid-resource"><code>init</code> callback</a>.</li> 4821cb0ef41Sopenharmony_ci<li><code>before</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> The <a href="#beforeasyncid"><code>before</code> callback</a>.</li> 4831cb0ef41Sopenharmony_ci<li><code>after</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> The <a href="#afterasyncid"><code>after</code> callback</a>.</li> 4841cb0ef41Sopenharmony_ci<li><code>destroy</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> The <a href="#destroyasyncid"><code>destroy</code> callback</a>.</li> 4851cb0ef41Sopenharmony_ci<li><code>promiseResolve</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> The <a href="#promiseresolveasyncid"><code>promiseResolve</code> callback</a>.</li> 4861cb0ef41Sopenharmony_ci</ul> 4871cb0ef41Sopenharmony_ci</li> 4881cb0ef41Sopenharmony_ci<li>Returns: <a href="async_hooks.html#async_hookscreatehookcallbacks" class="type"><AsyncHook></a> Instance used for disabling and enabling hooks</li> 4891cb0ef41Sopenharmony_ci</ul> 4901cb0ef41Sopenharmony_ci<p>Registers functions to be called for different lifetime events of each async 4911cb0ef41Sopenharmony_cioperation.</p> 4921cb0ef41Sopenharmony_ci<p>The callbacks <code>init()</code>/<code>before()</code>/<code>after()</code>/<code>destroy()</code> are called for the 4931cb0ef41Sopenharmony_cirespective asynchronous event during a resource's lifetime.</p> 4941cb0ef41Sopenharmony_ci<p>All callbacks are optional. For example, if only resource cleanup needs to 4951cb0ef41Sopenharmony_cibe tracked, then only the <code>destroy</code> callback needs to be passed. The 4961cb0ef41Sopenharmony_cispecifics of all functions that can be passed to <code>callbacks</code> is in the 4971cb0ef41Sopenharmony_ci<a href="#hook-callbacks">Hook Callbacks</a> section.</p> 4981cb0ef41Sopenharmony_ci 4991cb0ef41Sopenharmony_ci<pre class="with-48-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> { createHook } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:async_hooks'</span>; 5001cb0ef41Sopenharmony_ci 5011cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> asyncHook = <span class="hljs-title function_">createHook</span>({ 5021cb0ef41Sopenharmony_ci <span class="hljs-title function_">init</span>(<span class="hljs-params">asyncId, type, triggerAsyncId, resource</span>) { }, 5031cb0ef41Sopenharmony_ci <span class="hljs-title function_">destroy</span>(<span class="hljs-params">asyncId</span>) { }, 5041cb0ef41Sopenharmony_ci});</code><code class="language-js cjs"><span class="hljs-keyword">const</span> async_hooks = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:async_hooks'</span>); 5051cb0ef41Sopenharmony_ci 5061cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> asyncHook = async_hooks.<span class="hljs-title function_">createHook</span>({ 5071cb0ef41Sopenharmony_ci <span class="hljs-title function_">init</span>(<span class="hljs-params">asyncId, type, triggerAsyncId, resource</span>) { }, 5081cb0ef41Sopenharmony_ci <span class="hljs-title function_">destroy</span>(<span class="hljs-params">asyncId</span>) { }, 5091cb0ef41Sopenharmony_ci});</code><button class="copy-button">copy</button></pre> 5101cb0ef41Sopenharmony_ci<p>The callbacks will be inherited via the prototype chain:</p> 5111cb0ef41Sopenharmony_ci<pre><code class="language-js"><span class="hljs-keyword">class</span> <span class="hljs-title class_">MyAsyncCallbacks</span> { 5121cb0ef41Sopenharmony_ci <span class="hljs-title function_">init</span>(<span class="hljs-params">asyncId, type, triggerAsyncId, resource</span>) { } 5131cb0ef41Sopenharmony_ci <span class="hljs-title function_">destroy</span>(<span class="hljs-params">asyncId</span>) {} 5141cb0ef41Sopenharmony_ci} 5151cb0ef41Sopenharmony_ci 5161cb0ef41Sopenharmony_ci<span class="hljs-keyword">class</span> <span class="hljs-title class_">MyAddedCallbacks</span> <span class="hljs-keyword">extends</span> <span class="hljs-title class_ inherited__">MyAsyncCallbacks</span> { 5171cb0ef41Sopenharmony_ci <span class="hljs-title function_">before</span>(<span class="hljs-params">asyncId</span>) { } 5181cb0ef41Sopenharmony_ci <span class="hljs-title function_">after</span>(<span class="hljs-params">asyncId</span>) { } 5191cb0ef41Sopenharmony_ci} 5201cb0ef41Sopenharmony_ci 5211cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> asyncHook = async_hooks.<span class="hljs-title function_">createHook</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">MyAddedCallbacks</span>());</code> <button class="copy-button">copy</button></pre> 5221cb0ef41Sopenharmony_ci<p>Because promises are asynchronous resources whose lifecycle is tracked 5231cb0ef41Sopenharmony_civia the async hooks mechanism, the <code>init()</code>, <code>before()</code>, <code>after()</code>, and 5241cb0ef41Sopenharmony_ci<code>destroy()</code> callbacks <em>must not</em> be async functions that return promises.</p> 5251cb0ef41Sopenharmony_ci<h4>Error handling<span><a class="mark" href="#error-handling" id="error-handling">#</a></span><a aria-hidden="true" class="legacy" id="async_hooks_error_handling"></a></h4> 5261cb0ef41Sopenharmony_ci<p>If any <code>AsyncHook</code> callbacks throw, the application will print the stack trace 5271cb0ef41Sopenharmony_ciand exit. The exit path does follow that of an uncaught exception, but 5281cb0ef41Sopenharmony_ciall <code>'uncaughtException'</code> listeners are removed, thus forcing the process to 5291cb0ef41Sopenharmony_ciexit. The <code>'exit'</code> callbacks will still be called unless the application is run 5301cb0ef41Sopenharmony_ciwith <code>--abort-on-uncaught-exception</code>, in which case a stack trace will be 5311cb0ef41Sopenharmony_ciprinted and the application exits, leaving a core file.</p> 5321cb0ef41Sopenharmony_ci<p>The reason for this error handling behavior is that these callbacks are running 5331cb0ef41Sopenharmony_ciat potentially volatile points in an object's lifetime, for example during 5341cb0ef41Sopenharmony_ciclass construction and destruction. Because of this, it is deemed necessary to 5351cb0ef41Sopenharmony_cibring down the process quickly in order to prevent an unintentional abort in the 5361cb0ef41Sopenharmony_cifuture. This is subject to change in the future if a comprehensive analysis is 5371cb0ef41Sopenharmony_ciperformed to ensure an exception can follow the normal control flow without 5381cb0ef41Sopenharmony_ciunintentional side effects.</p> 5391cb0ef41Sopenharmony_ci<h4>Printing in <code>AsyncHook</code> callbacks<span><a class="mark" href="#printing-in-asynchook-callbacks" id="printing-in-asynchook-callbacks">#</a></span><a aria-hidden="true" class="legacy" id="async_hooks_printing_in_asynchook_callbacks"></a></h4> 5401cb0ef41Sopenharmony_ci<p>Because printing to the console is an asynchronous operation, <code>console.log()</code> 5411cb0ef41Sopenharmony_ciwill cause <code>AsyncHook</code> callbacks to be called. Using <code>console.log()</code> or 5421cb0ef41Sopenharmony_cisimilar asynchronous operations inside an <code>AsyncHook</code> callback function will 5431cb0ef41Sopenharmony_cicause an infinite recursion. An easy solution to this when debugging is to use a 5441cb0ef41Sopenharmony_cisynchronous logging operation such as <code>fs.writeFileSync(file, msg, flag)</code>. 5451cb0ef41Sopenharmony_ciThis will print to the file and will not invoke <code>AsyncHook</code> recursively because 5461cb0ef41Sopenharmony_ciit is synchronous.</p> 5471cb0ef41Sopenharmony_ci 5481cb0ef41Sopenharmony_ci<pre class="with-40-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> { writeFileSync } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:fs'</span>; 5491cb0ef41Sopenharmony_ci<span class="hljs-keyword">import</span> { format } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:util'</span>; 5501cb0ef41Sopenharmony_ci 5511cb0ef41Sopenharmony_ci<span class="hljs-keyword">function</span> <span class="hljs-title function_">debug</span>(<span class="hljs-params">...args</span>) { 5521cb0ef41Sopenharmony_ci <span class="hljs-comment">// Use a function like this one when debugging inside an AsyncHook callback</span> 5531cb0ef41Sopenharmony_ci <span class="hljs-title function_">writeFileSync</span>(<span class="hljs-string">'log.out'</span>, <span class="hljs-string">`<span class="hljs-subst">${format(...args)}</span>\n`</span>, { <span class="hljs-attr">flag</span>: <span class="hljs-string">'a'</span> }); 5541cb0ef41Sopenharmony_ci}</code><code class="language-js cjs"><span class="hljs-keyword">const</span> fs = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:fs'</span>); 5551cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>); 5561cb0ef41Sopenharmony_ci 5571cb0ef41Sopenharmony_ci<span class="hljs-keyword">function</span> <span class="hljs-title function_">debug</span>(<span class="hljs-params">...args</span>) { 5581cb0ef41Sopenharmony_ci <span class="hljs-comment">// Use a function like this one when debugging inside an AsyncHook callback</span> 5591cb0ef41Sopenharmony_ci fs.<span class="hljs-title function_">writeFileSync</span>(<span class="hljs-string">'log.out'</span>, <span class="hljs-string">`<span class="hljs-subst">${util.format(...args)}</span>\n`</span>, { <span class="hljs-attr">flag</span>: <span class="hljs-string">'a'</span> }); 5601cb0ef41Sopenharmony_ci}</code><button class="copy-button">copy</button></pre> 5611cb0ef41Sopenharmony_ci<p>If an asynchronous operation is needed for logging, it is possible to keep 5621cb0ef41Sopenharmony_citrack of what caused the asynchronous operation using the information 5631cb0ef41Sopenharmony_ciprovided by <code>AsyncHook</code> itself. The logging should then be skipped when 5641cb0ef41Sopenharmony_ciit was the logging itself that caused the <code>AsyncHook</code> callback to be called. By 5651cb0ef41Sopenharmony_cidoing this, the otherwise infinite recursion is broken.</p> 5661cb0ef41Sopenharmony_ci</section><section><h3>Class: <code>AsyncHook</code><span><a class="mark" href="#class-asynchook" id="class-asynchook">#</a></span><a aria-hidden="true" class="legacy" id="async_hooks_class_asynchook"></a></h3> 5671cb0ef41Sopenharmony_ci<p>The class <code>AsyncHook</code> exposes an interface for tracking lifetime events 5681cb0ef41Sopenharmony_ciof asynchronous operations.</p> 5691cb0ef41Sopenharmony_ci<h4><code>asyncHook.enable()</code><span><a class="mark" href="#asynchookenable" id="asynchookenable">#</a></span><a aria-hidden="true" class="legacy" id="async_hooks_asynchook_enable"></a></h4> 5701cb0ef41Sopenharmony_ci<ul> 5711cb0ef41Sopenharmony_ci<li>Returns: <a href="async_hooks.html#async_hookscreatehookcallbacks" class="type"><AsyncHook></a> A reference to <code>asyncHook</code>.</li> 5721cb0ef41Sopenharmony_ci</ul> 5731cb0ef41Sopenharmony_ci<p>Enable the callbacks for a given <code>AsyncHook</code> instance. If no callbacks are 5741cb0ef41Sopenharmony_ciprovided, enabling is a no-op.</p> 5751cb0ef41Sopenharmony_ci<p>The <code>AsyncHook</code> instance is disabled by default. If the <code>AsyncHook</code> instance 5761cb0ef41Sopenharmony_cishould be enabled immediately after creation, the following pattern can be used.</p> 5771cb0ef41Sopenharmony_ci 5781cb0ef41Sopenharmony_ci<pre class="with-48-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> { createHook } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:async_hooks'</span>; 5791cb0ef41Sopenharmony_ci 5801cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> hook = <span class="hljs-title function_">createHook</span>(callbacks).<span class="hljs-title function_">enable</span>();</code><code class="language-js cjs"><span class="hljs-keyword">const</span> async_hooks = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:async_hooks'</span>); 5811cb0ef41Sopenharmony_ci 5821cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> hook = async_hooks.<span class="hljs-title function_">createHook</span>(callbacks).<span class="hljs-title function_">enable</span>();</code><button class="copy-button">copy</button></pre> 5831cb0ef41Sopenharmony_ci<h4><code>asyncHook.disable()</code><span><a class="mark" href="#asynchookdisable" id="asynchookdisable">#</a></span><a aria-hidden="true" class="legacy" id="async_hooks_asynchook_disable"></a></h4> 5841cb0ef41Sopenharmony_ci<ul> 5851cb0ef41Sopenharmony_ci<li>Returns: <a href="async_hooks.html#async_hookscreatehookcallbacks" class="type"><AsyncHook></a> A reference to <code>asyncHook</code>.</li> 5861cb0ef41Sopenharmony_ci</ul> 5871cb0ef41Sopenharmony_ci<p>Disable the callbacks for a given <code>AsyncHook</code> instance from the global pool of 5881cb0ef41Sopenharmony_ci<code>AsyncHook</code> callbacks to be executed. Once a hook has been disabled it will not 5891cb0ef41Sopenharmony_cibe called again until enabled.</p> 5901cb0ef41Sopenharmony_ci<p>For API consistency <code>disable()</code> also returns the <code>AsyncHook</code> instance.</p> 5911cb0ef41Sopenharmony_ci<h4>Hook callbacks<span><a class="mark" href="#hook-callbacks" id="hook-callbacks">#</a></span><a aria-hidden="true" class="legacy" id="async_hooks_hook_callbacks"></a></h4> 5921cb0ef41Sopenharmony_ci<p>Key events in the lifetime of asynchronous events have been categorized into 5931cb0ef41Sopenharmony_cifour areas: instantiation, before/after the callback is called, and when the 5941cb0ef41Sopenharmony_ciinstance is destroyed.</p> 5951cb0ef41Sopenharmony_ci<h5><code>init(asyncId, type, triggerAsyncId, resource)</code><span><a class="mark" href="#initasyncid-type-triggerasyncid-resource" id="initasyncid-type-triggerasyncid-resource">#</a></span><a aria-hidden="true" class="legacy" id="async_hooks_init_asyncid_type_triggerasyncid_resource"></a></h5> 5961cb0ef41Sopenharmony_ci<ul> 5971cb0ef41Sopenharmony_ci<li><code>asyncId</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> A unique ID for the async resource.</li> 5981cb0ef41Sopenharmony_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 the async resource.</li> 5991cb0ef41Sopenharmony_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 unique ID of the async resource in whose 6001cb0ef41Sopenharmony_ciexecution context this async resource was created.</li> 6011cb0ef41Sopenharmony_ci<li><code>resource</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> Reference to the resource representing the async 6021cb0ef41Sopenharmony_cioperation, needs to be released during <em>destroy</em>.</li> 6031cb0ef41Sopenharmony_ci</ul> 6041cb0ef41Sopenharmony_ci<p>Called when a class is constructed that has the <em>possibility</em> to emit an 6051cb0ef41Sopenharmony_ciasynchronous event. This <em>does not</em> mean the instance must call 6061cb0ef41Sopenharmony_ci<code>before</code>/<code>after</code> before <code>destroy</code> is called, only that the possibility 6071cb0ef41Sopenharmony_ciexists.</p> 6081cb0ef41Sopenharmony_ci<p>This behavior can be observed by doing something like opening a resource then 6091cb0ef41Sopenharmony_ciclosing it before the resource can be used. The following snippet demonstrates 6101cb0ef41Sopenharmony_cithis.</p> 6111cb0ef41Sopenharmony_ci 6121cb0ef41Sopenharmony_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:net'</span>; 6131cb0ef41Sopenharmony_ci 6141cb0ef41Sopenharmony_ci<span class="hljs-title function_">createServer</span>().<span class="hljs-title function_">listen</span>(<span class="hljs-keyword">function</span>(<span class="hljs-params"></span>) { <span class="hljs-variable language_">this</span>.<span class="hljs-title function_">close</span>(); }); 6151cb0ef41Sopenharmony_ci<span class="hljs-comment">// OR</span> 6161cb0ef41Sopenharmony_ci<span class="hljs-built_in">clearTimeout</span>(<span class="hljs-built_in">setTimeout</span>(<span class="hljs-function">() =></span> {}, <span class="hljs-number">10</span>));</code><code class="language-js cjs"><span class="hljs-built_in">require</span>(<span class="hljs-string">'node:net'</span>).<span class="hljs-title function_">createServer</span>().<span class="hljs-title function_">listen</span>(<span class="hljs-keyword">function</span>(<span class="hljs-params"></span>) { <span class="hljs-variable language_">this</span>.<span class="hljs-title function_">close</span>(); }); 6171cb0ef41Sopenharmony_ci<span class="hljs-comment">// OR</span> 6181cb0ef41Sopenharmony_ci<span class="hljs-built_in">clearTimeout</span>(<span class="hljs-built_in">setTimeout</span>(<span class="hljs-function">() =></span> {}, <span class="hljs-number">10</span>));</code><button class="copy-button">copy</button></pre> 6191cb0ef41Sopenharmony_ci<p>Every new resource is assigned an ID that is unique within the scope of the 6201cb0ef41Sopenharmony_cicurrent Node.js instance.</p> 6211cb0ef41Sopenharmony_ci<h6><code>type</code><span><a class="mark" href="#type" id="type">#</a></span><a aria-hidden="true" class="legacy" id="async_hooks_type"></a></h6> 6221cb0ef41Sopenharmony_ci<p>The <code>type</code> is a string identifying the type of resource that caused 6231cb0ef41Sopenharmony_ci<code>init</code> to be called. Generally, it will correspond to the name of the 6241cb0ef41Sopenharmony_ciresource's constructor.</p> 6251cb0ef41Sopenharmony_ci<p>The <code>type</code> of resources created by Node.js itself can change in any Node.js 6261cb0ef41Sopenharmony_cirelease. Valid values include <code>TLSWRAP</code>, 6271cb0ef41Sopenharmony_ci<code>TCPWRAP</code>, <code>TCPSERVERWRAP</code>, <code>GETADDRINFOREQWRAP</code>, <code>FSREQCALLBACK</code>, 6281cb0ef41Sopenharmony_ci<code>Microtask</code>, and <code>Timeout</code>. Inspect the source code of the Node.js version used 6291cb0ef41Sopenharmony_cito get the full list.</p> 6301cb0ef41Sopenharmony_ci<p>Furthermore users of <a href="async_context.html#class-asyncresource"><code>AsyncResource</code></a> create async resources independent 6311cb0ef41Sopenharmony_ciof Node.js itself.</p> 6321cb0ef41Sopenharmony_ci<p>There is also the <code>PROMISE</code> resource type, which is used to track <code>Promise</code> 6331cb0ef41Sopenharmony_ciinstances and asynchronous work scheduled by them.</p> 6341cb0ef41Sopenharmony_ci<p>Users are able to define their own <code>type</code> when using the public embedder API.</p> 6351cb0ef41Sopenharmony_ci<p>It is possible to have type name collisions. Embedders are encouraged to use 6361cb0ef41Sopenharmony_ciunique prefixes, such as the npm package name, to prevent collisions when 6371cb0ef41Sopenharmony_cilistening to the hooks.</p> 6381cb0ef41Sopenharmony_ci<h6><code>triggerAsyncId</code><span><a class="mark" href="#triggerasyncid" id="triggerasyncid">#</a></span><a aria-hidden="true" class="legacy" id="async_hooks_triggerasyncid"></a></h6> 6391cb0ef41Sopenharmony_ci<p><code>triggerAsyncId</code> is the <code>asyncId</code> of the resource that caused (or "triggered") 6401cb0ef41Sopenharmony_cithe new resource to initialize and that caused <code>init</code> to call. This is different 6411cb0ef41Sopenharmony_cifrom <code>async_hooks.executionAsyncId()</code> that only shows <em>when</em> a resource was 6421cb0ef41Sopenharmony_cicreated, while <code>triggerAsyncId</code> shows <em>why</em> a resource was created.</p> 6431cb0ef41Sopenharmony_ci<p>The following is a simple demonstration of <code>triggerAsyncId</code>:</p> 6441cb0ef41Sopenharmony_ci 6451cb0ef41Sopenharmony_ci<pre class="with-69-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> { createHook, executionAsyncId } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:async_hooks'</span>; 6461cb0ef41Sopenharmony_ci<span class="hljs-keyword">import</span> { stdout } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:process'</span>; 6471cb0ef41Sopenharmony_ci<span class="hljs-keyword">import</span> net <span class="hljs-keyword">from</span> <span class="hljs-string">'node:net'</span>; 6481cb0ef41Sopenharmony_ci<span class="hljs-keyword">import</span> fs <span class="hljs-keyword">from</span> <span class="hljs-string">'node:fs'</span>; 6491cb0ef41Sopenharmony_ci 6501cb0ef41Sopenharmony_ci<span class="hljs-title function_">createHook</span>({ 6511cb0ef41Sopenharmony_ci <span class="hljs-title function_">init</span>(<span class="hljs-params">asyncId, type, triggerAsyncId</span>) { 6521cb0ef41Sopenharmony_ci <span class="hljs-keyword">const</span> eid = <span class="hljs-title function_">executionAsyncId</span>(); 6531cb0ef41Sopenharmony_ci fs.<span class="hljs-title function_">writeSync</span>( 6541cb0ef41Sopenharmony_ci stdout.<span class="hljs-property">fd</span>, 6551cb0ef41Sopenharmony_ci <span class="hljs-string">`<span class="hljs-subst">${type}</span>(<span class="hljs-subst">${asyncId}</span>): trigger: <span class="hljs-subst">${triggerAsyncId}</span> execution: <span class="hljs-subst">${eid}</span>\n`</span>); 6561cb0ef41Sopenharmony_ci }, 6571cb0ef41Sopenharmony_ci}).<span class="hljs-title function_">enable</span>(); 6581cb0ef41Sopenharmony_ci 6591cb0ef41Sopenharmony_cinet.<span class="hljs-title function_">createServer</span>(<span class="hljs-function">(<span class="hljs-params">conn</span>) =></span> {}).<span class="hljs-title function_">listen</span>(<span class="hljs-number">8080</span>);</code><code class="language-js cjs"><span class="hljs-keyword">const</span> { createHook, executionAsyncId } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:async_hooks'</span>); 6601cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> { stdout } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:process'</span>); 6611cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> net = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:net'</span>); 6621cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> fs = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:fs'</span>); 6631cb0ef41Sopenharmony_ci 6641cb0ef41Sopenharmony_ci<span class="hljs-title function_">createHook</span>({ 6651cb0ef41Sopenharmony_ci <span class="hljs-title function_">init</span>(<span class="hljs-params">asyncId, type, triggerAsyncId</span>) { 6661cb0ef41Sopenharmony_ci <span class="hljs-keyword">const</span> eid = <span class="hljs-title function_">executionAsyncId</span>(); 6671cb0ef41Sopenharmony_ci fs.<span class="hljs-title function_">writeSync</span>( 6681cb0ef41Sopenharmony_ci stdout.<span class="hljs-property">fd</span>, 6691cb0ef41Sopenharmony_ci <span class="hljs-string">`<span class="hljs-subst">${type}</span>(<span class="hljs-subst">${asyncId}</span>): trigger: <span class="hljs-subst">${triggerAsyncId}</span> execution: <span class="hljs-subst">${eid}</span>\n`</span>); 6701cb0ef41Sopenharmony_ci }, 6711cb0ef41Sopenharmony_ci}).<span class="hljs-title function_">enable</span>(); 6721cb0ef41Sopenharmony_ci 6731cb0ef41Sopenharmony_cinet.<span class="hljs-title function_">createServer</span>(<span class="hljs-function">(<span class="hljs-params">conn</span>) =></span> {}).<span class="hljs-title function_">listen</span>(<span class="hljs-number">8080</span>);</code><button class="copy-button">copy</button></pre> 6741cb0ef41Sopenharmony_ci<p>Output when hitting the server with <code>nc localhost 8080</code>:</p> 6751cb0ef41Sopenharmony_ci<pre><code class="language-console">TCPSERVERWRAP(5): trigger: 1 execution: 1 6761cb0ef41Sopenharmony_ciTCPWRAP(7): trigger: 5 execution: 0</code> <button class="copy-button">copy</button></pre> 6771cb0ef41Sopenharmony_ci<p>The <code>TCPSERVERWRAP</code> is the server which receives the connections.</p> 6781cb0ef41Sopenharmony_ci<p>The <code>TCPWRAP</code> is the new connection from the client. When a new 6791cb0ef41Sopenharmony_ciconnection is made, the <code>TCPWrap</code> instance is immediately constructed. This 6801cb0ef41Sopenharmony_cihappens outside of any JavaScript stack. (An <code>executionAsyncId()</code> of <code>0</code> means 6811cb0ef41Sopenharmony_cithat it is being executed from C++ with no JavaScript stack above it.) With only 6821cb0ef41Sopenharmony_cithat information, it would be impossible to link resources together in 6831cb0ef41Sopenharmony_citerms of what caused them to be created, so <code>triggerAsyncId</code> is given the task 6841cb0ef41Sopenharmony_ciof propagating what resource is responsible for the new resource's existence.</p> 6851cb0ef41Sopenharmony_ci<h6><code>resource</code><span><a class="mark" href="#resource" id="resource">#</a></span><a aria-hidden="true" class="legacy" id="async_hooks_resource"></a></h6> 6861cb0ef41Sopenharmony_ci<p><code>resource</code> is an object that represents the actual async resource that has 6871cb0ef41Sopenharmony_cibeen initialized. The API to access the object may be specified by the 6881cb0ef41Sopenharmony_cicreator of the resource. Resources created by Node.js itself are internal 6891cb0ef41Sopenharmony_ciand may change at any time. Therefore no API is specified for these.</p> 6901cb0ef41Sopenharmony_ci<p>In some cases the resource object is reused for performance reasons, it is 6911cb0ef41Sopenharmony_cithus not safe to use it as a key in a <code>WeakMap</code> or add properties to it.</p> 6921cb0ef41Sopenharmony_ci<h6>Asynchronous context example<span><a class="mark" href="#asynchronous-context-example" id="asynchronous-context-example">#</a></span><a aria-hidden="true" class="legacy" id="async_hooks_asynchronous_context_example"></a></h6> 6931cb0ef41Sopenharmony_ci<p>The context tracking use case is covered by the stable API <a href="async_context.html#class-asynclocalstorage"><code>AsyncLocalStorage</code></a>. 6941cb0ef41Sopenharmony_ciThis example only illustrates async hooks operation but <a href="async_context.html#class-asynclocalstorage"><code>AsyncLocalStorage</code></a> 6951cb0ef41Sopenharmony_cifits better to this use case.</p> 6961cb0ef41Sopenharmony_ci<p>The following is an example with additional information about the calls to 6971cb0ef41Sopenharmony_ci<code>init</code> between the <code>before</code> and <code>after</code> calls, specifically what the 6981cb0ef41Sopenharmony_cicallback to <code>listen()</code> will look like. The output formatting is slightly more 6991cb0ef41Sopenharmony_cielaborate to make calling context easier to see.</p> 7001cb0ef41Sopenharmony_ci 7011cb0ef41Sopenharmony_ci<pre class="with-48-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> async_hooks <span class="hljs-keyword">from</span> <span class="hljs-string">'node:async_hooks'</span>; 7021cb0ef41Sopenharmony_ci<span class="hljs-keyword">import</span> fs <span class="hljs-keyword">from</span> <span class="hljs-string">'node:fs'</span>; 7031cb0ef41Sopenharmony_ci<span class="hljs-keyword">import</span> net <span class="hljs-keyword">from</span> <span class="hljs-string">'node:net'</span>; 7041cb0ef41Sopenharmony_ci<span class="hljs-keyword">import</span> { stdout } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:process'</span>; 7051cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> { fd } = stdout; 7061cb0ef41Sopenharmony_ci 7071cb0ef41Sopenharmony_ci<span class="hljs-keyword">let</span> indent = <span class="hljs-number">0</span>; 7081cb0ef41Sopenharmony_ciasync_hooks.<span class="hljs-title function_">createHook</span>({ 7091cb0ef41Sopenharmony_ci <span class="hljs-title function_">init</span>(<span class="hljs-params">asyncId, type, triggerAsyncId</span>) { 7101cb0ef41Sopenharmony_ci <span class="hljs-keyword">const</span> eid = async_hooks.<span class="hljs-title function_">executionAsyncId</span>(); 7111cb0ef41Sopenharmony_ci <span class="hljs-keyword">const</span> indentStr = <span class="hljs-string">' '</span>.<span class="hljs-title function_">repeat</span>(indent); 7121cb0ef41Sopenharmony_ci fs.<span class="hljs-title function_">writeSync</span>( 7131cb0ef41Sopenharmony_ci fd, 7141cb0ef41Sopenharmony_ci <span class="hljs-string">`<span class="hljs-subst">${indentStr}</span><span class="hljs-subst">${type}</span>(<span class="hljs-subst">${asyncId}</span>):`</span> + 7151cb0ef41Sopenharmony_ci <span class="hljs-string">` trigger: <span class="hljs-subst">${triggerAsyncId}</span> execution: <span class="hljs-subst">${eid}</span>\n`</span>); 7161cb0ef41Sopenharmony_ci }, 7171cb0ef41Sopenharmony_ci <span class="hljs-title function_">before</span>(<span class="hljs-params">asyncId</span>) { 7181cb0ef41Sopenharmony_ci <span class="hljs-keyword">const</span> indentStr = <span class="hljs-string">' '</span>.<span class="hljs-title function_">repeat</span>(indent); 7191cb0ef41Sopenharmony_ci fs.<span class="hljs-title function_">writeSync</span>(fd, <span class="hljs-string">`<span class="hljs-subst">${indentStr}</span>before: <span class="hljs-subst">${asyncId}</span>\n`</span>); 7201cb0ef41Sopenharmony_ci indent += <span class="hljs-number">2</span>; 7211cb0ef41Sopenharmony_ci }, 7221cb0ef41Sopenharmony_ci <span class="hljs-title function_">after</span>(<span class="hljs-params">asyncId</span>) { 7231cb0ef41Sopenharmony_ci indent -= <span class="hljs-number">2</span>; 7241cb0ef41Sopenharmony_ci <span class="hljs-keyword">const</span> indentStr = <span class="hljs-string">' '</span>.<span class="hljs-title function_">repeat</span>(indent); 7251cb0ef41Sopenharmony_ci fs.<span class="hljs-title function_">writeSync</span>(fd, <span class="hljs-string">`<span class="hljs-subst">${indentStr}</span>after: <span class="hljs-subst">${asyncId}</span>\n`</span>); 7261cb0ef41Sopenharmony_ci }, 7271cb0ef41Sopenharmony_ci <span class="hljs-title function_">destroy</span>(<span class="hljs-params">asyncId</span>) { 7281cb0ef41Sopenharmony_ci <span class="hljs-keyword">const</span> indentStr = <span class="hljs-string">' '</span>.<span class="hljs-title function_">repeat</span>(indent); 7291cb0ef41Sopenharmony_ci fs.<span class="hljs-title function_">writeSync</span>(fd, <span class="hljs-string">`<span class="hljs-subst">${indentStr}</span>destroy: <span class="hljs-subst">${asyncId}</span>\n`</span>); 7301cb0ef41Sopenharmony_ci }, 7311cb0ef41Sopenharmony_ci}).<span class="hljs-title function_">enable</span>(); 7321cb0ef41Sopenharmony_ci 7331cb0ef41Sopenharmony_cinet.<span class="hljs-title function_">createServer</span>(<span class="hljs-function">() =></span> {}).<span class="hljs-title function_">listen</span>(<span class="hljs-number">8080</span>, <span class="hljs-function">() =></span> { 7341cb0ef41Sopenharmony_ci <span class="hljs-comment">// Let's wait 10ms before logging the server started.</span> 7351cb0ef41Sopenharmony_ci <span class="hljs-built_in">setTimeout</span>(<span class="hljs-function">() =></span> { 7361cb0ef41Sopenharmony_ci <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">'>>>'</span>, async_hooks.<span class="hljs-title function_">executionAsyncId</span>()); 7371cb0ef41Sopenharmony_ci }, <span class="hljs-number">10</span>); 7381cb0ef41Sopenharmony_ci});</code><code class="language-js cjs"><span class="hljs-keyword">const</span> async_hooks = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:async_hooks'</span>); 7391cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> fs = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:fs'</span>); 7401cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> net = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:net'</span>); 7411cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> { fd } = process.<span class="hljs-property">stdout</span>; 7421cb0ef41Sopenharmony_ci 7431cb0ef41Sopenharmony_ci<span class="hljs-keyword">let</span> indent = <span class="hljs-number">0</span>; 7441cb0ef41Sopenharmony_ciasync_hooks.<span class="hljs-title function_">createHook</span>({ 7451cb0ef41Sopenharmony_ci <span class="hljs-title function_">init</span>(<span class="hljs-params">asyncId, type, triggerAsyncId</span>) { 7461cb0ef41Sopenharmony_ci <span class="hljs-keyword">const</span> eid = async_hooks.<span class="hljs-title function_">executionAsyncId</span>(); 7471cb0ef41Sopenharmony_ci <span class="hljs-keyword">const</span> indentStr = <span class="hljs-string">' '</span>.<span class="hljs-title function_">repeat</span>(indent); 7481cb0ef41Sopenharmony_ci fs.<span class="hljs-title function_">writeSync</span>( 7491cb0ef41Sopenharmony_ci fd, 7501cb0ef41Sopenharmony_ci <span class="hljs-string">`<span class="hljs-subst">${indentStr}</span><span class="hljs-subst">${type}</span>(<span class="hljs-subst">${asyncId}</span>):`</span> + 7511cb0ef41Sopenharmony_ci <span class="hljs-string">` trigger: <span class="hljs-subst">${triggerAsyncId}</span> execution: <span class="hljs-subst">${eid}</span>\n`</span>); 7521cb0ef41Sopenharmony_ci }, 7531cb0ef41Sopenharmony_ci <span class="hljs-title function_">before</span>(<span class="hljs-params">asyncId</span>) { 7541cb0ef41Sopenharmony_ci <span class="hljs-keyword">const</span> indentStr = <span class="hljs-string">' '</span>.<span class="hljs-title function_">repeat</span>(indent); 7551cb0ef41Sopenharmony_ci fs.<span class="hljs-title function_">writeSync</span>(fd, <span class="hljs-string">`<span class="hljs-subst">${indentStr}</span>before: <span class="hljs-subst">${asyncId}</span>\n`</span>); 7561cb0ef41Sopenharmony_ci indent += <span class="hljs-number">2</span>; 7571cb0ef41Sopenharmony_ci }, 7581cb0ef41Sopenharmony_ci <span class="hljs-title function_">after</span>(<span class="hljs-params">asyncId</span>) { 7591cb0ef41Sopenharmony_ci indent -= <span class="hljs-number">2</span>; 7601cb0ef41Sopenharmony_ci <span class="hljs-keyword">const</span> indentStr = <span class="hljs-string">' '</span>.<span class="hljs-title function_">repeat</span>(indent); 7611cb0ef41Sopenharmony_ci fs.<span class="hljs-title function_">writeSync</span>(fd, <span class="hljs-string">`<span class="hljs-subst">${indentStr}</span>after: <span class="hljs-subst">${asyncId}</span>\n`</span>); 7621cb0ef41Sopenharmony_ci }, 7631cb0ef41Sopenharmony_ci <span class="hljs-title function_">destroy</span>(<span class="hljs-params">asyncId</span>) { 7641cb0ef41Sopenharmony_ci <span class="hljs-keyword">const</span> indentStr = <span class="hljs-string">' '</span>.<span class="hljs-title function_">repeat</span>(indent); 7651cb0ef41Sopenharmony_ci fs.<span class="hljs-title function_">writeSync</span>(fd, <span class="hljs-string">`<span class="hljs-subst">${indentStr}</span>destroy: <span class="hljs-subst">${asyncId}</span>\n`</span>); 7661cb0ef41Sopenharmony_ci }, 7671cb0ef41Sopenharmony_ci}).<span class="hljs-title function_">enable</span>(); 7681cb0ef41Sopenharmony_ci 7691cb0ef41Sopenharmony_cinet.<span class="hljs-title function_">createServer</span>(<span class="hljs-function">() =></span> {}).<span class="hljs-title function_">listen</span>(<span class="hljs-number">8080</span>, <span class="hljs-function">() =></span> { 7701cb0ef41Sopenharmony_ci <span class="hljs-comment">// Let's wait 10ms before logging the server started.</span> 7711cb0ef41Sopenharmony_ci <span class="hljs-built_in">setTimeout</span>(<span class="hljs-function">() =></span> { 7721cb0ef41Sopenharmony_ci <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">'>>>'</span>, async_hooks.<span class="hljs-title function_">executionAsyncId</span>()); 7731cb0ef41Sopenharmony_ci }, <span class="hljs-number">10</span>); 7741cb0ef41Sopenharmony_ci});</code><button class="copy-button">copy</button></pre> 7751cb0ef41Sopenharmony_ci<p>Output from only starting the server:</p> 7761cb0ef41Sopenharmony_ci<pre><code class="language-console">TCPSERVERWRAP(5): trigger: 1 execution: 1 7771cb0ef41Sopenharmony_ciTickObject(6): trigger: 5 execution: 1 7781cb0ef41Sopenharmony_cibefore: 6 7791cb0ef41Sopenharmony_ci Timeout(7): trigger: 6 execution: 6 7801cb0ef41Sopenharmony_ciafter: 6 7811cb0ef41Sopenharmony_cidestroy: 6 7821cb0ef41Sopenharmony_cibefore: 7 7831cb0ef41Sopenharmony_ci<span class="hljs-meta prompt_">></span><span class="language-bash">>> 7</span> 7841cb0ef41Sopenharmony_ci TickObject(8): trigger: 7 execution: 7 7851cb0ef41Sopenharmony_ciafter: 7 7861cb0ef41Sopenharmony_cibefore: 8 7871cb0ef41Sopenharmony_ciafter: 8</code> <button class="copy-button">copy</button></pre> 7881cb0ef41Sopenharmony_ci<p>As illustrated in the example, <code>executionAsyncId()</code> and <code>execution</code> each specify 7891cb0ef41Sopenharmony_cithe value of the current execution context; which is delineated by calls to 7901cb0ef41Sopenharmony_ci<code>before</code> and <code>after</code>.</p> 7911cb0ef41Sopenharmony_ci<p>Only using <code>execution</code> to graph resource allocation results in the following:</p> 7921cb0ef41Sopenharmony_ci<pre><code class="language-console"> root(1) 7931cb0ef41Sopenharmony_ci ^ 7941cb0ef41Sopenharmony_ci | 7951cb0ef41Sopenharmony_ciTickObject(6) 7961cb0ef41Sopenharmony_ci ^ 7971cb0ef41Sopenharmony_ci | 7981cb0ef41Sopenharmony_ci Timeout(7)</code> <button class="copy-button">copy</button></pre> 7991cb0ef41Sopenharmony_ci<p>The <code>TCPSERVERWRAP</code> is not part of this graph, even though it was the reason for 8001cb0ef41Sopenharmony_ci<code>console.log()</code> being called. This is because binding to a port without a host 8011cb0ef41Sopenharmony_ciname is a <em>synchronous</em> operation, but to maintain a completely asynchronous 8021cb0ef41Sopenharmony_ciAPI the user's callback is placed in a <code>process.nextTick()</code>. Which is why 8031cb0ef41Sopenharmony_ci<code>TickObject</code> is present in the output and is a 'parent' for <code>.listen()</code> 8041cb0ef41Sopenharmony_cicallback.</p> 8051cb0ef41Sopenharmony_ci<p>The graph only shows <em>when</em> a resource was created, not <em>why</em>, so to track 8061cb0ef41Sopenharmony_cithe <em>why</em> use <code>triggerAsyncId</code>. Which can be represented with the following 8071cb0ef41Sopenharmony_cigraph:</p> 8081cb0ef41Sopenharmony_ci<pre><code class="language-console"> bootstrap(1) 8091cb0ef41Sopenharmony_ci | 8101cb0ef41Sopenharmony_ci ˅ 8111cb0ef41Sopenharmony_ciTCPSERVERWRAP(5) 8121cb0ef41Sopenharmony_ci | 8131cb0ef41Sopenharmony_ci ˅ 8141cb0ef41Sopenharmony_ci TickObject(6) 8151cb0ef41Sopenharmony_ci | 8161cb0ef41Sopenharmony_ci ˅ 8171cb0ef41Sopenharmony_ci Timeout(7)</code> <button class="copy-button">copy</button></pre> 8181cb0ef41Sopenharmony_ci<h5><code>before(asyncId)</code><span><a class="mark" href="#beforeasyncid" id="beforeasyncid">#</a></span><a aria-hidden="true" class="legacy" id="async_hooks_before_asyncid"></a></h5> 8191cb0ef41Sopenharmony_ci<ul> 8201cb0ef41Sopenharmony_ci<li><code>asyncId</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 8211cb0ef41Sopenharmony_ci</ul> 8221cb0ef41Sopenharmony_ci<p>When an asynchronous operation is initiated (such as a TCP server receiving a 8231cb0ef41Sopenharmony_cinew connection) or completes (such as writing data to disk) a callback is 8241cb0ef41Sopenharmony_cicalled to notify the user. The <code>before</code> callback is called just before said 8251cb0ef41Sopenharmony_cicallback is executed. <code>asyncId</code> is the unique identifier assigned to the 8261cb0ef41Sopenharmony_ciresource about to execute the callback.</p> 8271cb0ef41Sopenharmony_ci<p>The <code>before</code> callback will be called 0 to N times. The <code>before</code> callback 8281cb0ef41Sopenharmony_ciwill typically be called 0 times if the asynchronous operation was cancelled 8291cb0ef41Sopenharmony_cior, for example, if no connections are received by a TCP server. Persistent 8301cb0ef41Sopenharmony_ciasynchronous resources like a TCP server will typically call the <code>before</code> 8311cb0ef41Sopenharmony_cicallback multiple times, while other operations like <code>fs.open()</code> will call 8321cb0ef41Sopenharmony_ciit only once.</p> 8331cb0ef41Sopenharmony_ci<h5><code>after(asyncId)</code><span><a class="mark" href="#afterasyncid" id="afterasyncid">#</a></span><a aria-hidden="true" class="legacy" id="async_hooks_after_asyncid"></a></h5> 8341cb0ef41Sopenharmony_ci<ul> 8351cb0ef41Sopenharmony_ci<li><code>asyncId</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 8361cb0ef41Sopenharmony_ci</ul> 8371cb0ef41Sopenharmony_ci<p>Called immediately after the callback specified in <code>before</code> is completed.</p> 8381cb0ef41Sopenharmony_ci<p>If an uncaught exception occurs during execution of the callback, then <code>after</code> 8391cb0ef41Sopenharmony_ciwill run <em>after</em> the <code>'uncaughtException'</code> event is emitted or a <code>domain</code>'s 8401cb0ef41Sopenharmony_cihandler runs.</p> 8411cb0ef41Sopenharmony_ci<h5><code>destroy(asyncId)</code><span><a class="mark" href="#destroyasyncid" id="destroyasyncid">#</a></span><a aria-hidden="true" class="legacy" id="async_hooks_destroy_asyncid"></a></h5> 8421cb0ef41Sopenharmony_ci<ul> 8431cb0ef41Sopenharmony_ci<li><code>asyncId</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 8441cb0ef41Sopenharmony_ci</ul> 8451cb0ef41Sopenharmony_ci<p>Called after the resource corresponding to <code>asyncId</code> is destroyed. It is also 8461cb0ef41Sopenharmony_cicalled asynchronously from the embedder API <code>emitDestroy()</code>.</p> 8471cb0ef41Sopenharmony_ci<p>Some resources depend on garbage collection for cleanup, so if a reference is 8481cb0ef41Sopenharmony_cimade to the <code>resource</code> object passed to <code>init</code> it is possible that <code>destroy</code> 8491cb0ef41Sopenharmony_ciwill never be called, causing a memory leak in the application. If the resource 8501cb0ef41Sopenharmony_cidoes not depend on garbage collection, then this will not be an issue.</p> 8511cb0ef41Sopenharmony_ci<p>Using the destroy hook results in additional overhead because it enables 8521cb0ef41Sopenharmony_citracking of <code>Promise</code> instances via the garbage collector.</p> 8531cb0ef41Sopenharmony_ci<h5><code>promiseResolve(asyncId)</code><span><a class="mark" href="#promiseresolveasyncid" id="promiseresolveasyncid">#</a></span><a aria-hidden="true" class="legacy" id="async_hooks_promiseresolve_asyncid"></a></h5> 8541cb0ef41Sopenharmony_ci<div class="api_metadata"> 8551cb0ef41Sopenharmony_ci<span>Added in: v8.6.0</span> 8561cb0ef41Sopenharmony_ci</div> 8571cb0ef41Sopenharmony_ci<ul> 8581cb0ef41Sopenharmony_ci<li><code>asyncId</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 8591cb0ef41Sopenharmony_ci</ul> 8601cb0ef41Sopenharmony_ci<p>Called when the <code>resolve</code> function passed to the <code>Promise</code> constructor is 8611cb0ef41Sopenharmony_ciinvoked (either directly or through other means of resolving a promise).</p> 8621cb0ef41Sopenharmony_ci<p><code>resolve()</code> does not do any observable synchronous work.</p> 8631cb0ef41Sopenharmony_ci<p>The <code>Promise</code> is not necessarily fulfilled or rejected at this point if the 8641cb0ef41Sopenharmony_ci<code>Promise</code> was resolved by assuming the state of another <code>Promise</code>.</p> 8651cb0ef41Sopenharmony_ci<pre><code class="language-js"><span class="hljs-keyword">new</span> <span class="hljs-title class_">Promise</span>(<span class="hljs-function">(<span class="hljs-params">resolve</span>) =></span> <span class="hljs-title function_">resolve</span>(<span class="hljs-literal">true</span>)).<span class="hljs-title function_">then</span>(<span class="hljs-function">(<span class="hljs-params">a</span>) =></span> {});</code> <button class="copy-button">copy</button></pre> 8661cb0ef41Sopenharmony_ci<p>calls the following callbacks:</p> 8671cb0ef41Sopenharmony_ci<pre><code class="language-text">init for PROMISE with id 5, trigger id: 1 8681cb0ef41Sopenharmony_ci promise resolve 5 # corresponds to resolve(true) 8691cb0ef41Sopenharmony_ciinit for PROMISE with id 6, trigger id: 5 # the Promise returned by then() 8701cb0ef41Sopenharmony_ci before 6 # the then() callback is entered 8711cb0ef41Sopenharmony_ci promise resolve 6 # the then() callback resolves the promise by returning 8721cb0ef41Sopenharmony_ci after 6</code> <button class="copy-button">copy</button></pre> 8731cb0ef41Sopenharmony_ci<h4><code>async_hooks.executionAsyncResource()</code><span><a class="mark" href="#async_hooksexecutionasyncresource" id="async_hooksexecutionasyncresource">#</a></span><a aria-hidden="true" class="legacy" id="async_hooks_async_hooks_executionasyncresource"></a></h4> 8741cb0ef41Sopenharmony_ci<div class="api_metadata"> 8751cb0ef41Sopenharmony_ci<span>Added in: v13.9.0, v12.17.0</span> 8761cb0ef41Sopenharmony_ci</div> 8771cb0ef41Sopenharmony_ci<ul> 8781cb0ef41Sopenharmony_ci<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> The resource representing the current execution. 8791cb0ef41Sopenharmony_ciUseful to store data within the resource.</li> 8801cb0ef41Sopenharmony_ci</ul> 8811cb0ef41Sopenharmony_ci<p>Resource objects returned by <code>executionAsyncResource()</code> are most often internal 8821cb0ef41Sopenharmony_ciNode.js handle objects with undocumented APIs. Using any functions or properties 8831cb0ef41Sopenharmony_cion the object is likely to crash your application and should be avoided.</p> 8841cb0ef41Sopenharmony_ci<p>Using <code>executionAsyncResource()</code> in the top-level execution context will 8851cb0ef41Sopenharmony_cireturn an empty object as there is no handle or request object to use, 8861cb0ef41Sopenharmony_cibut having an object representing the top-level can be helpful.</p> 8871cb0ef41Sopenharmony_ci 8881cb0ef41Sopenharmony_ci<pre class="with-81-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> { open } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:fs'</span>; 8891cb0ef41Sopenharmony_ci<span class="hljs-keyword">import</span> { executionAsyncId, executionAsyncResource } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:async_hooks'</span>; 8901cb0ef41Sopenharmony_ci 8911cb0ef41Sopenharmony_ci<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-title function_">executionAsyncId</span>(), <span class="hljs-title function_">executionAsyncResource</span>()); <span class="hljs-comment">// 1 {}</span> 8921cb0ef41Sopenharmony_ci<span class="hljs-title function_">open</span>(<span class="hljs-keyword">new</span> <span class="hljs-title function_">URL</span>(<span class="hljs-keyword">import</span>.<span class="hljs-property">meta</span>.<span class="hljs-property">url</span>), <span class="hljs-string">'r'</span>, <span class="hljs-function">(<span class="hljs-params">err, fd</span>) =></span> { 8931cb0ef41Sopenharmony_ci <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-title function_">executionAsyncId</span>(), <span class="hljs-title function_">executionAsyncResource</span>()); <span class="hljs-comment">// 7 FSReqWrap</span> 8941cb0ef41Sopenharmony_ci});</code><code class="language-js cjs"><span class="hljs-keyword">const</span> { open } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:fs'</span>); 8951cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> { executionAsyncId, executionAsyncResource } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:async_hooks'</span>); 8961cb0ef41Sopenharmony_ci 8971cb0ef41Sopenharmony_ci<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-title function_">executionAsyncId</span>(), <span class="hljs-title function_">executionAsyncResource</span>()); <span class="hljs-comment">// 1 {}</span> 8981cb0ef41Sopenharmony_ci<span class="hljs-title function_">open</span>(__filename, <span class="hljs-string">'r'</span>, <span class="hljs-function">(<span class="hljs-params">err, fd</span>) =></span> { 8991cb0ef41Sopenharmony_ci <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-title function_">executionAsyncId</span>(), <span class="hljs-title function_">executionAsyncResource</span>()); <span class="hljs-comment">// 7 FSReqWrap</span> 9001cb0ef41Sopenharmony_ci});</code><button class="copy-button">copy</button></pre> 9011cb0ef41Sopenharmony_ci<p>This can be used to implement continuation local storage without the 9021cb0ef41Sopenharmony_ciuse of a tracking <code>Map</code> to store the metadata:</p> 9031cb0ef41Sopenharmony_ci 9041cb0ef41Sopenharmony_ci<pre class="with-46-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>; 9051cb0ef41Sopenharmony_ci<span class="hljs-keyword">import</span> { 9061cb0ef41Sopenharmony_ci executionAsyncId, 9071cb0ef41Sopenharmony_ci executionAsyncResource, 9081cb0ef41Sopenharmony_ci createHook, 9091cb0ef41Sopenharmony_ci} <span class="hljs-keyword">from</span> <span class="hljs-string">'async_hooks'</span>; 9101cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> sym = <span class="hljs-title class_">Symbol</span>(<span class="hljs-string">'state'</span>); <span class="hljs-comment">// Private symbol to avoid pollution</span> 9111cb0ef41Sopenharmony_ci 9121cb0ef41Sopenharmony_ci<span class="hljs-title function_">createHook</span>({ 9131cb0ef41Sopenharmony_ci <span class="hljs-title function_">init</span>(<span class="hljs-params">asyncId, type, triggerAsyncId, resource</span>) { 9141cb0ef41Sopenharmony_ci <span class="hljs-keyword">const</span> cr = <span class="hljs-title function_">executionAsyncResource</span>(); 9151cb0ef41Sopenharmony_ci <span class="hljs-keyword">if</span> (cr) { 9161cb0ef41Sopenharmony_ci resource[sym] = cr[sym]; 9171cb0ef41Sopenharmony_ci } 9181cb0ef41Sopenharmony_ci }, 9191cb0ef41Sopenharmony_ci}).<span class="hljs-title function_">enable</span>(); 9201cb0ef41Sopenharmony_ci 9211cb0ef41Sopenharmony_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> { 9221cb0ef41Sopenharmony_ci <span class="hljs-title function_">executionAsyncResource</span>()[sym] = { <span class="hljs-attr">state</span>: req.<span class="hljs-property">url</span> }; 9231cb0ef41Sopenharmony_ci <span class="hljs-built_in">setTimeout</span>(<span class="hljs-keyword">function</span>(<span class="hljs-params"></span>) { 9241cb0ef41Sopenharmony_ci res.<span class="hljs-title function_">end</span>(<span class="hljs-title class_">JSON</span>.<span class="hljs-title function_">stringify</span>(<span class="hljs-title function_">executionAsyncResource</span>()[sym])); 9251cb0ef41Sopenharmony_ci }, <span class="hljs-number">100</span>); 9261cb0ef41Sopenharmony_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>); 9271cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> { 9281cb0ef41Sopenharmony_ci executionAsyncId, 9291cb0ef41Sopenharmony_ci executionAsyncResource, 9301cb0ef41Sopenharmony_ci createHook, 9311cb0ef41Sopenharmony_ci} = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:async_hooks'</span>); 9321cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> sym = <span class="hljs-title class_">Symbol</span>(<span class="hljs-string">'state'</span>); <span class="hljs-comment">// Private symbol to avoid pollution</span> 9331cb0ef41Sopenharmony_ci 9341cb0ef41Sopenharmony_ci<span class="hljs-title function_">createHook</span>({ 9351cb0ef41Sopenharmony_ci <span class="hljs-title function_">init</span>(<span class="hljs-params">asyncId, type, triggerAsyncId, resource</span>) { 9361cb0ef41Sopenharmony_ci <span class="hljs-keyword">const</span> cr = <span class="hljs-title function_">executionAsyncResource</span>(); 9371cb0ef41Sopenharmony_ci <span class="hljs-keyword">if</span> (cr) { 9381cb0ef41Sopenharmony_ci resource[sym] = cr[sym]; 9391cb0ef41Sopenharmony_ci } 9401cb0ef41Sopenharmony_ci }, 9411cb0ef41Sopenharmony_ci}).<span class="hljs-title function_">enable</span>(); 9421cb0ef41Sopenharmony_ci 9431cb0ef41Sopenharmony_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> { 9441cb0ef41Sopenharmony_ci <span class="hljs-title function_">executionAsyncResource</span>()[sym] = { <span class="hljs-attr">state</span>: req.<span class="hljs-property">url</span> }; 9451cb0ef41Sopenharmony_ci <span class="hljs-built_in">setTimeout</span>(<span class="hljs-keyword">function</span>(<span class="hljs-params"></span>) { 9461cb0ef41Sopenharmony_ci res.<span class="hljs-title function_">end</span>(<span class="hljs-title class_">JSON</span>.<span class="hljs-title function_">stringify</span>(<span class="hljs-title function_">executionAsyncResource</span>()[sym])); 9471cb0ef41Sopenharmony_ci }, <span class="hljs-number">100</span>); 9481cb0ef41Sopenharmony_ci}).<span class="hljs-title function_">listen</span>(<span class="hljs-number">3000</span>);</code><button class="copy-button">copy</button></pre> 9491cb0ef41Sopenharmony_ci<h4><code>async_hooks.executionAsyncId()</code><span><a class="mark" href="#async_hooksexecutionasyncid" id="async_hooksexecutionasyncid">#</a></span><a aria-hidden="true" class="legacy" id="async_hooks_async_hooks_executionasyncid"></a></h4> 9501cb0ef41Sopenharmony_ci<div class="api_metadata"> 9511cb0ef41Sopenharmony_ci<details class="changelog"><summary>History</summary> 9521cb0ef41Sopenharmony_ci<table> 9531cb0ef41Sopenharmony_ci<tbody><tr><th>Version</th><th>Changes</th></tr> 9541cb0ef41Sopenharmony_ci<tr><td>v8.2.0</td> 9551cb0ef41Sopenharmony_ci<td><p>Renamed from <code>currentId</code>.</p></td></tr> 9561cb0ef41Sopenharmony_ci<tr><td>v8.1.0</td> 9571cb0ef41Sopenharmony_ci<td><p><span>Added in: v8.1.0</span></p></td></tr> 9581cb0ef41Sopenharmony_ci</tbody></table> 9591cb0ef41Sopenharmony_ci</details> 9601cb0ef41Sopenharmony_ci</div> 9611cb0ef41Sopenharmony_ci<ul> 9621cb0ef41Sopenharmony_ci<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> The <code>asyncId</code> of the current execution context. Useful to 9631cb0ef41Sopenharmony_citrack when something calls.</li> 9641cb0ef41Sopenharmony_ci</ul> 9651cb0ef41Sopenharmony_ci 9661cb0ef41Sopenharmony_ci<pre class="with-52-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> { executionAsyncId } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:async_hooks'</span>; 9671cb0ef41Sopenharmony_ci<span class="hljs-keyword">import</span> fs <span class="hljs-keyword">from</span> <span class="hljs-string">'node:fs'</span>; 9681cb0ef41Sopenharmony_ci 9691cb0ef41Sopenharmony_ci<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-title function_">executionAsyncId</span>()); <span class="hljs-comment">// 1 - bootstrap</span> 9701cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> path = <span class="hljs-string">'.'</span>; 9711cb0ef41Sopenharmony_cifs.<span class="hljs-title function_">open</span>(path, <span class="hljs-string">'r'</span>, <span class="hljs-function">(<span class="hljs-params">err, fd</span>) =></span> { 9721cb0ef41Sopenharmony_ci <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-title function_">executionAsyncId</span>()); <span class="hljs-comment">// 6 - open()</span> 9731cb0ef41Sopenharmony_ci});</code><code class="language-js cjs"><span class="hljs-keyword">const</span> async_hooks = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:async_hooks'</span>); 9741cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> fs = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:fs'</span>); 9751cb0ef41Sopenharmony_ci 9761cb0ef41Sopenharmony_ci<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(async_hooks.<span class="hljs-title function_">executionAsyncId</span>()); <span class="hljs-comment">// 1 - bootstrap</span> 9771cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> path = <span class="hljs-string">'.'</span>; 9781cb0ef41Sopenharmony_cifs.<span class="hljs-title function_">open</span>(path, <span class="hljs-string">'r'</span>, <span class="hljs-function">(<span class="hljs-params">err, fd</span>) =></span> { 9791cb0ef41Sopenharmony_ci <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(async_hooks.<span class="hljs-title function_">executionAsyncId</span>()); <span class="hljs-comment">// 6 - open()</span> 9801cb0ef41Sopenharmony_ci});</code><button class="copy-button">copy</button></pre> 9811cb0ef41Sopenharmony_ci<p>The ID returned from <code>executionAsyncId()</code> is related to execution timing, not 9821cb0ef41Sopenharmony_cicausality (which is covered by <code>triggerAsyncId()</code>):</p> 9831cb0ef41Sopenharmony_ci<pre><code class="language-js"><span class="hljs-keyword">const</span> server = net.<span class="hljs-title function_">createServer</span>(<span class="hljs-function">(<span class="hljs-params">conn</span>) =></span> { 9841cb0ef41Sopenharmony_ci <span class="hljs-comment">// Returns the ID of the server, not of the new connection, because the</span> 9851cb0ef41Sopenharmony_ci <span class="hljs-comment">// callback runs in the execution scope of the server's MakeCallback().</span> 9861cb0ef41Sopenharmony_ci async_hooks.<span class="hljs-title function_">executionAsyncId</span>(); 9871cb0ef41Sopenharmony_ci 9881cb0ef41Sopenharmony_ci}).<span class="hljs-title function_">listen</span>(port, <span class="hljs-function">() =></span> { 9891cb0ef41Sopenharmony_ci <span class="hljs-comment">// Returns the ID of a TickObject (process.nextTick()) because all</span> 9901cb0ef41Sopenharmony_ci <span class="hljs-comment">// callbacks passed to .listen() are wrapped in a nextTick().</span> 9911cb0ef41Sopenharmony_ci async_hooks.<span class="hljs-title function_">executionAsyncId</span>(); 9921cb0ef41Sopenharmony_ci});</code> <button class="copy-button">copy</button></pre> 9931cb0ef41Sopenharmony_ci<p>Promise contexts may not get precise <code>executionAsyncIds</code> by default. 9941cb0ef41Sopenharmony_ciSee the section on <a href="#promise-execution-tracking">promise execution tracking</a>.</p> 9951cb0ef41Sopenharmony_ci<h4><code>async_hooks.triggerAsyncId()</code><span><a class="mark" href="#async_hookstriggerasyncid" id="async_hookstriggerasyncid">#</a></span><a aria-hidden="true" class="legacy" id="async_hooks_async_hooks_triggerasyncid"></a></h4> 9961cb0ef41Sopenharmony_ci<ul> 9971cb0ef41Sopenharmony_ci<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> The ID of the resource responsible for calling the callback 9981cb0ef41Sopenharmony_cithat is currently being executed.</li> 9991cb0ef41Sopenharmony_ci</ul> 10001cb0ef41Sopenharmony_ci<pre><code class="language-js"><span class="hljs-keyword">const</span> server = net.<span class="hljs-title function_">createServer</span>(<span class="hljs-function">(<span class="hljs-params">conn</span>) =></span> { 10011cb0ef41Sopenharmony_ci <span class="hljs-comment">// The resource that caused (or triggered) this callback to be called</span> 10021cb0ef41Sopenharmony_ci <span class="hljs-comment">// was that of the new connection. Thus the return value of triggerAsyncId()</span> 10031cb0ef41Sopenharmony_ci <span class="hljs-comment">// is the asyncId of "conn".</span> 10041cb0ef41Sopenharmony_ci async_hooks.<span class="hljs-title function_">triggerAsyncId</span>(); 10051cb0ef41Sopenharmony_ci 10061cb0ef41Sopenharmony_ci}).<span class="hljs-title function_">listen</span>(port, <span class="hljs-function">() =></span> { 10071cb0ef41Sopenharmony_ci <span class="hljs-comment">// Even though all callbacks passed to .listen() are wrapped in a nextTick()</span> 10081cb0ef41Sopenharmony_ci <span class="hljs-comment">// the callback itself exists because the call to the server's .listen()</span> 10091cb0ef41Sopenharmony_ci <span class="hljs-comment">// was made. So the return value would be the ID of the server.</span> 10101cb0ef41Sopenharmony_ci async_hooks.<span class="hljs-title function_">triggerAsyncId</span>(); 10111cb0ef41Sopenharmony_ci});</code> <button class="copy-button">copy</button></pre> 10121cb0ef41Sopenharmony_ci<p>Promise contexts may not get valid <code>triggerAsyncId</code>s by default. See 10131cb0ef41Sopenharmony_cithe section on <a href="#promise-execution-tracking">promise execution tracking</a>.</p> 10141cb0ef41Sopenharmony_ci<h4><code>async_hooks.asyncWrapProviders</code><span><a class="mark" href="#async_hooksasyncwrapproviders" id="async_hooksasyncwrapproviders">#</a></span><a aria-hidden="true" class="legacy" id="async_hooks_async_hooks_asyncwrapproviders"></a></h4> 10151cb0ef41Sopenharmony_ci<div class="api_metadata"> 10161cb0ef41Sopenharmony_ci<span>Added in: v17.2.0, v16.14.0</span> 10171cb0ef41Sopenharmony_ci</div> 10181cb0ef41Sopenharmony_ci<ul> 10191cb0ef41Sopenharmony_ci<li>Returns: A map of provider types to the corresponding numeric id. 10201cb0ef41Sopenharmony_ciThis map contains all the event types that might be emitted by the <code>async_hooks.init()</code> event.</li> 10211cb0ef41Sopenharmony_ci</ul> 10221cb0ef41Sopenharmony_ci<p>This feature suppresses the deprecated usage of <code>process.binding('async_wrap').Providers</code>. 10231cb0ef41Sopenharmony_ciSee: <a href="deprecations.html#dep0111-processbinding">DEP0111</a></p> 10241cb0ef41Sopenharmony_ci</section><section><h3>Promise execution tracking<span><a class="mark" href="#promise-execution-tracking" id="promise-execution-tracking">#</a></span><a aria-hidden="true" class="legacy" id="async_hooks_promise_execution_tracking"></a></h3> 10251cb0ef41Sopenharmony_ci<p>By default, promise executions are not assigned <code>asyncId</code>s due to the relatively 10261cb0ef41Sopenharmony_ciexpensive nature of the <a href="https://docs.google.com/document/d/1rda3yKGHimKIhg5YeoAmCOtyURgsbTH_qaYR79FELlk/edit">promise introspection API</a> provided by 10271cb0ef41Sopenharmony_ciV8. This means that programs using promises or <code>async</code>/<code>await</code> will not get 10281cb0ef41Sopenharmony_cicorrect execution and trigger ids for promise callback contexts by default.</p> 10291cb0ef41Sopenharmony_ci 10301cb0ef41Sopenharmony_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> { executionAsyncId, triggerAsyncId } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:async_hooks'</span>; 10311cb0ef41Sopenharmony_ci 10321cb0ef41Sopenharmony_ci<span class="hljs-title class_">Promise</span>.<span class="hljs-title function_">resolve</span>(<span class="hljs-number">1729</span>).<span class="hljs-title function_">then</span>(<span class="hljs-function">() =></span> { 10331cb0ef41Sopenharmony_ci <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">`eid <span class="hljs-subst">${executionAsyncId()}</span> tid <span class="hljs-subst">${triggerAsyncId()}</span>`</span>); 10341cb0ef41Sopenharmony_ci}); 10351cb0ef41Sopenharmony_ci<span class="hljs-comment">// produces:</span> 10361cb0ef41Sopenharmony_ci<span class="hljs-comment">// eid 1 tid 0</span></code><code class="language-js cjs"><span class="hljs-keyword">const</span> { executionAsyncId, triggerAsyncId } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:async_hooks'</span>); 10371cb0ef41Sopenharmony_ci 10381cb0ef41Sopenharmony_ci<span class="hljs-title class_">Promise</span>.<span class="hljs-title function_">resolve</span>(<span class="hljs-number">1729</span>).<span class="hljs-title function_">then</span>(<span class="hljs-function">() =></span> { 10391cb0ef41Sopenharmony_ci <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">`eid <span class="hljs-subst">${executionAsyncId()}</span> tid <span class="hljs-subst">${triggerAsyncId()}</span>`</span>); 10401cb0ef41Sopenharmony_ci}); 10411cb0ef41Sopenharmony_ci<span class="hljs-comment">// produces:</span> 10421cb0ef41Sopenharmony_ci<span class="hljs-comment">// eid 1 tid 0</span></code><button class="copy-button">copy</button></pre> 10431cb0ef41Sopenharmony_ci<p>Observe that the <code>then()</code> callback claims to have executed in the context of the 10441cb0ef41Sopenharmony_ciouter scope even though there was an asynchronous hop involved. Also, 10451cb0ef41Sopenharmony_cithe <code>triggerAsyncId</code> value is <code>0</code>, which means that we are missing context about 10461cb0ef41Sopenharmony_cithe resource that caused (triggered) the <code>then()</code> callback to be executed.</p> 10471cb0ef41Sopenharmony_ci<p>Installing async hooks via <code>async_hooks.createHook</code> enables promise execution 10481cb0ef41Sopenharmony_citracking:</p> 10491cb0ef41Sopenharmony_ci 10501cb0ef41Sopenharmony_ci<pre class="with-85-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> { createHook, executionAsyncId, triggerAsyncId } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:async_hooks'</span>; 10511cb0ef41Sopenharmony_ci<span class="hljs-title function_">createHook</span>({ <span class="hljs-title function_">init</span>(<span class="hljs-params"></span>) {} }).<span class="hljs-title function_">enable</span>(); <span class="hljs-comment">// forces PromiseHooks to be enabled.</span> 10521cb0ef41Sopenharmony_ci<span class="hljs-title class_">Promise</span>.<span class="hljs-title function_">resolve</span>(<span class="hljs-number">1729</span>).<span class="hljs-title function_">then</span>(<span class="hljs-function">() =></span> { 10531cb0ef41Sopenharmony_ci <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">`eid <span class="hljs-subst">${executionAsyncId()}</span> tid <span class="hljs-subst">${triggerAsyncId()}</span>`</span>); 10541cb0ef41Sopenharmony_ci}); 10551cb0ef41Sopenharmony_ci<span class="hljs-comment">// produces:</span> 10561cb0ef41Sopenharmony_ci<span class="hljs-comment">// eid 7 tid 6</span></code><code class="language-js cjs"><span class="hljs-keyword">const</span> { createHook, executionAsyncId, triggerAsyncId } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:async_hooks'</span>); 10571cb0ef41Sopenharmony_ci 10581cb0ef41Sopenharmony_ci<span class="hljs-title function_">createHook</span>({ <span class="hljs-title function_">init</span>(<span class="hljs-params"></span>) {} }).<span class="hljs-title function_">enable</span>(); <span class="hljs-comment">// forces PromiseHooks to be enabled.</span> 10591cb0ef41Sopenharmony_ci<span class="hljs-title class_">Promise</span>.<span class="hljs-title function_">resolve</span>(<span class="hljs-number">1729</span>).<span class="hljs-title function_">then</span>(<span class="hljs-function">() =></span> { 10601cb0ef41Sopenharmony_ci <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">`eid <span class="hljs-subst">${executionAsyncId()}</span> tid <span class="hljs-subst">${triggerAsyncId()}</span>`</span>); 10611cb0ef41Sopenharmony_ci}); 10621cb0ef41Sopenharmony_ci<span class="hljs-comment">// produces:</span> 10631cb0ef41Sopenharmony_ci<span class="hljs-comment">// eid 7 tid 6</span></code><button class="copy-button">copy</button></pre> 10641cb0ef41Sopenharmony_ci<p>In this example, adding any actual hook function enabled the tracking of 10651cb0ef41Sopenharmony_cipromises. There are two promises in the example above; the promise created by 10661cb0ef41Sopenharmony_ci<code>Promise.resolve()</code> and the promise returned by the call to <code>then()</code>. In the 10671cb0ef41Sopenharmony_ciexample above, the first promise got the <code>asyncId</code> <code>6</code> and the latter got 10681cb0ef41Sopenharmony_ci<code>asyncId</code> <code>7</code>. During the execution of the <code>then()</code> callback, we are executing 10691cb0ef41Sopenharmony_ciin the context of promise with <code>asyncId</code> <code>7</code>. This promise was triggered by 10701cb0ef41Sopenharmony_ciasync resource <code>6</code>.</p> 10711cb0ef41Sopenharmony_ci<p>Another subtlety with promises is that <code>before</code> and <code>after</code> callbacks are run 10721cb0ef41Sopenharmony_cionly on chained promises. That means promises not created by <code>then()</code>/<code>catch()</code> 10731cb0ef41Sopenharmony_ciwill not have the <code>before</code> and <code>after</code> callbacks fired on them. For more details 10741cb0ef41Sopenharmony_cisee the details of the V8 <a href="https://docs.google.com/document/d/1rda3yKGHimKIhg5YeoAmCOtyURgsbTH_qaYR79FELlk/edit">PromiseHooks</a> API.</p> 10751cb0ef41Sopenharmony_ci</section><section><h3>JavaScript embedder API<span><a class="mark" href="#javascript-embedder-api" id="javascript-embedder-api">#</a></span><a aria-hidden="true" class="legacy" id="async_hooks_javascript_embedder_api"></a></h3> 10761cb0ef41Sopenharmony_ci<p>Library developers that handle their own asynchronous resources performing tasks 10771cb0ef41Sopenharmony_cilike I/O, connection pooling, or managing callback queues may use the 10781cb0ef41Sopenharmony_ci<code>AsyncResource</code> JavaScript API so that all the appropriate callbacks are called.</p> 10791cb0ef41Sopenharmony_ci<h4>Class: <code>AsyncResource</code><span><a class="mark" href="#class-asyncresource" id="class-asyncresource">#</a></span><a aria-hidden="true" class="legacy" id="async_hooks_class_asyncresource"></a></h4> 10801cb0ef41Sopenharmony_ci<p>The documentation for this class has moved <a href="async_context.html#class-asyncresource"><code>AsyncResource</code></a>.</p> 10811cb0ef41Sopenharmony_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_hooks_class_asynclocalstorage"></a></h3> 10821cb0ef41Sopenharmony_ci<p>The documentation for this class has moved <a href="async_context.html#class-asynclocalstorage"><code>AsyncLocalStorage</code></a>.</p></section> 10831cb0ef41Sopenharmony_ci <!-- API END --> 10841cb0ef41Sopenharmony_ci </div> 10851cb0ef41Sopenharmony_ci </div> 10861cb0ef41Sopenharmony_ci </div> 10871cb0ef41Sopenharmony_ci</body> 10881cb0ef41Sopenharmony_ci</html> 1089