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1001cb0ef41Sopenharmony_ci <button class="theme-toggle-btn" id="theme-toggle-btn" title="Toggle dark mode/light mode" 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="#trace-events">Trace events</a></span> 1241cb0ef41Sopenharmony_ci<ul> 1251cb0ef41Sopenharmony_ci<li><a href="#the-nodetrace_events-module">The <code>node:trace_events</code> module</a> 1261cb0ef41Sopenharmony_ci<ul> 1271cb0ef41Sopenharmony_ci<li><a href="#tracing-object"><code>Tracing</code> object</a> 1281cb0ef41Sopenharmony_ci<ul> 1291cb0ef41Sopenharmony_ci<li><a href="#tracingcategories"><code>tracing.categories</code></a></li> 1301cb0ef41Sopenharmony_ci<li><a href="#tracingdisable"><code>tracing.disable()</code></a></li> 1311cb0ef41Sopenharmony_ci<li><a href="#tracingenable"><code>tracing.enable()</code></a></li> 1321cb0ef41Sopenharmony_ci<li><a href="#tracingenabled"><code>tracing.enabled</code></a></li> 1331cb0ef41Sopenharmony_ci</ul> 1341cb0ef41Sopenharmony_ci</li> 1351cb0ef41Sopenharmony_ci<li><a href="#trace_eventscreatetracingoptions"><code>trace_events.createTracing(options)</code></a></li> 1361cb0ef41Sopenharmony_ci<li><a href="#trace_eventsgetenabledcategories"><code>trace_events.getEnabledCategories()</code></a></li> 1371cb0ef41Sopenharmony_ci</ul> 1381cb0ef41Sopenharmony_ci</li> 1391cb0ef41Sopenharmony_ci<li><a href="#examples">Examples</a> 1401cb0ef41Sopenharmony_ci<ul> 1411cb0ef41Sopenharmony_ci<li><a href="#collect-trace-events-data-by-inspector">Collect trace events data by inspector</a></li> 1421cb0ef41Sopenharmony_ci</ul> 1431cb0ef41Sopenharmony_ci</li> 1441cb0ef41Sopenharmony_ci</ul> 1451cb0ef41Sopenharmony_ci</li> 1461cb0ef41Sopenharmony_ci</ul></div></div> 1471cb0ef41Sopenharmony_ci </li> 1481cb0ef41Sopenharmony_ci 1491cb0ef41Sopenharmony_ci 1501cb0ef41Sopenharmony_ci <li class="picker-header"> 1511cb0ef41Sopenharmony_ci <a href="#"> 1521cb0ef41Sopenharmony_ci <span class="collapsed-arrow">►</span><span class="expanded-arrow">▼</span> 1531cb0ef41Sopenharmony_ci Index 1541cb0ef41Sopenharmony_ci </a> 1551cb0ef41Sopenharmony_ci 1561cb0ef41Sopenharmony_ci <div class="picker"><ul> 1571cb0ef41Sopenharmony_ci<li><a href="documentation.html" class="nav-documentation">About this documentation</a></li> 1581cb0ef41Sopenharmony_ci<li><a href="synopsis.html" class="nav-synopsis">Usage and example</a></li> 1591cb0ef41Sopenharmony_ci 1601cb0ef41Sopenharmony_ci <li> 1611cb0ef41Sopenharmony_ci <a href="index.html">Index</a> 1621cb0ef41Sopenharmony_ci </li> 1631cb0ef41Sopenharmony_ci </ul> 1641cb0ef41Sopenharmony_ci 1651cb0ef41Sopenharmony_ci<hr class="line"> 1661cb0ef41Sopenharmony_ci<ul> 1671cb0ef41Sopenharmony_ci<li><a href="assert.html" class="nav-assert">Assertion testing</a></li> 1681cb0ef41Sopenharmony_ci<li><a href="async_context.html" class="nav-async_context">Asynchronous context tracking</a></li> 1691cb0ef41Sopenharmony_ci<li><a href="async_hooks.html" class="nav-async_hooks">Async hooks</a></li> 1701cb0ef41Sopenharmony_ci<li><a href="buffer.html" 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class="nav-webcrypto">Web Crypto API</a></li> 2241cb0ef41Sopenharmony_ci<li><a href="webstreams.html" class="nav-webstreams">Web Streams API</a></li> 2251cb0ef41Sopenharmony_ci<li><a href="worker_threads.html" class="nav-worker_threads">Worker threads</a></li> 2261cb0ef41Sopenharmony_ci<li><a href="zlib.html" class="nav-zlib">Zlib</a></li> 2271cb0ef41Sopenharmony_ci</ul> 2281cb0ef41Sopenharmony_ci<hr class="line"> 2291cb0ef41Sopenharmony_ci<ul> 2301cb0ef41Sopenharmony_ci<li><a href="https://github.com/nodejs/node" class="nav-https-github-com-nodejs-node">Code repository and issue tracker</a></li> 2311cb0ef41Sopenharmony_ci</ul></div> 2321cb0ef41Sopenharmony_ci </li> 2331cb0ef41Sopenharmony_ci 2341cb0ef41Sopenharmony_ci 2351cb0ef41Sopenharmony_ci <li class="picker-header"> 2361cb0ef41Sopenharmony_ci <a href="#"> 2371cb0ef41Sopenharmony_ci <span class="collapsed-arrow">►</span><span class="expanded-arrow">▼</span> 2381cb0ef41Sopenharmony_ci Other versions 2391cb0ef41Sopenharmony_ci </a> 2401cb0ef41Sopenharmony_ci <div class="picker"><ol id="alt-docs"><li><a href="https://nodejs.org/docs/latest-v21.x/api/tracing.html">21.x</a></li> 2411cb0ef41Sopenharmony_ci<li><a href="https://nodejs.org/docs/latest-v20.x/api/tracing.html">20.x <b>LTS</b></a></li> 2421cb0ef41Sopenharmony_ci<li><a href="https://nodejs.org/docs/latest-v19.x/api/tracing.html">19.x</a></li> 2431cb0ef41Sopenharmony_ci<li><a href="https://nodejs.org/docs/latest-v18.x/api/tracing.html">18.x <b>LTS</b></a></li> 2441cb0ef41Sopenharmony_ci<li><a href="https://nodejs.org/docs/latest-v17.x/api/tracing.html">17.x</a></li> 2451cb0ef41Sopenharmony_ci<li><a href="https://nodejs.org/docs/latest-v16.x/api/tracing.html">16.x</a></li> 2461cb0ef41Sopenharmony_ci<li><a href="https://nodejs.org/docs/latest-v15.x/api/tracing.html">15.x</a></li> 2471cb0ef41Sopenharmony_ci<li><a href="https://nodejs.org/docs/latest-v14.x/api/tracing.html">14.x</a></li> 2481cb0ef41Sopenharmony_ci<li><a href="https://nodejs.org/docs/latest-v13.x/api/tracing.html">13.x</a></li> 2491cb0ef41Sopenharmony_ci<li><a href="https://nodejs.org/docs/latest-v12.x/api/tracing.html">12.x</a></li> 2501cb0ef41Sopenharmony_ci<li><a href="https://nodejs.org/docs/latest-v11.x/api/tracing.html">11.x</a></li> 2511cb0ef41Sopenharmony_ci<li><a href="https://nodejs.org/docs/latest-v10.x/api/tracing.html">10.x</a></li> 2521cb0ef41Sopenharmony_ci<li><a href="https://nodejs.org/docs/latest-v9.x/api/tracing.html">9.x</a></li> 2531cb0ef41Sopenharmony_ci<li><a href="https://nodejs.org/docs/latest-v8.x/api/tracing.html">8.x</a></li> 2541cb0ef41Sopenharmony_ci<li><a href="https://nodejs.org/docs/latest-v7.x/api/tracing.html">7.x</a></li></ol></div> 2551cb0ef41Sopenharmony_ci </li> 2561cb0ef41Sopenharmony_ci 2571cb0ef41Sopenharmony_ci <li class="picker-header"> 2581cb0ef41Sopenharmony_ci <a href="#"> 2591cb0ef41Sopenharmony_ci <span class="collapsed-arrow">►</span><span class="expanded-arrow">▼</span> 2601cb0ef41Sopenharmony_ci Options 2611cb0ef41Sopenharmony_ci </a> 2621cb0ef41Sopenharmony_ci 2631cb0ef41Sopenharmony_ci <div class="picker"> 2641cb0ef41Sopenharmony_ci <ul> 2651cb0ef41Sopenharmony_ci <li> 2661cb0ef41Sopenharmony_ci <a href="all.html">View on single page</a> 2671cb0ef41Sopenharmony_ci </li> 2681cb0ef41Sopenharmony_ci <li> 2691cb0ef41Sopenharmony_ci <a href="tracing.json">View as JSON</a> 2701cb0ef41Sopenharmony_ci </li> 2711cb0ef41Sopenharmony_ci <li class="edit_on_github"><a href="https://github.com/nodejs/node/edit/main/doc/api/tracing.md">Edit on GitHub</a></li> 2721cb0ef41Sopenharmony_ci </ul> 2731cb0ef41Sopenharmony_ci </div> 2741cb0ef41Sopenharmony_ci </li> 2751cb0ef41Sopenharmony_ci </ul> 2761cb0ef41Sopenharmony_ci </div> 2771cb0ef41Sopenharmony_ci <hr> 2781cb0ef41Sopenharmony_ci </header> 2791cb0ef41Sopenharmony_ci 2801cb0ef41Sopenharmony_ci <details id="toc" open><summary>Table of contents</summary><ul> 2811cb0ef41Sopenharmony_ci<li><span class="stability_1"><a href="#trace-events">Trace events</a></span> 2821cb0ef41Sopenharmony_ci<ul> 2831cb0ef41Sopenharmony_ci<li><a href="#the-nodetrace_events-module">The <code>node:trace_events</code> module</a> 2841cb0ef41Sopenharmony_ci<ul> 2851cb0ef41Sopenharmony_ci<li><a href="#tracing-object"><code>Tracing</code> object</a> 2861cb0ef41Sopenharmony_ci<ul> 2871cb0ef41Sopenharmony_ci<li><a href="#tracingcategories"><code>tracing.categories</code></a></li> 2881cb0ef41Sopenharmony_ci<li><a href="#tracingdisable"><code>tracing.disable()</code></a></li> 2891cb0ef41Sopenharmony_ci<li><a href="#tracingenable"><code>tracing.enable()</code></a></li> 2901cb0ef41Sopenharmony_ci<li><a href="#tracingenabled"><code>tracing.enabled</code></a></li> 2911cb0ef41Sopenharmony_ci</ul> 2921cb0ef41Sopenharmony_ci</li> 2931cb0ef41Sopenharmony_ci<li><a href="#trace_eventscreatetracingoptions"><code>trace_events.createTracing(options)</code></a></li> 2941cb0ef41Sopenharmony_ci<li><a href="#trace_eventsgetenabledcategories"><code>trace_events.getEnabledCategories()</code></a></li> 2951cb0ef41Sopenharmony_ci</ul> 2961cb0ef41Sopenharmony_ci</li> 2971cb0ef41Sopenharmony_ci<li><a href="#examples">Examples</a> 2981cb0ef41Sopenharmony_ci<ul> 2991cb0ef41Sopenharmony_ci<li><a href="#collect-trace-events-data-by-inspector">Collect trace events data by inspector</a></li> 3001cb0ef41Sopenharmony_ci</ul> 3011cb0ef41Sopenharmony_ci</li> 3021cb0ef41Sopenharmony_ci</ul> 3031cb0ef41Sopenharmony_ci</li> 3041cb0ef41Sopenharmony_ci</ul></details> 3051cb0ef41Sopenharmony_ci 3061cb0ef41Sopenharmony_ci <div id="apicontent"> 3071cb0ef41Sopenharmony_ci <h2>Trace events<span><a class="mark" href="#trace-events" id="trace-events">#</a></span><a aria-hidden="true" class="legacy" id="tracing_trace_events"></a></h2> 3081cb0ef41Sopenharmony_ci 3091cb0ef41Sopenharmony_ci<p></p><div class="api_stability api_stability_1"><a href="documentation.html#stability-index">Stability: 1</a> - Experimental</div><p></p> 3101cb0ef41Sopenharmony_ci<p><strong>Source Code:</strong> <a href="https://github.com/nodejs/node/blob/v18.20.1/lib/trace_events.js">lib/trace_events.js</a></p> 3111cb0ef41Sopenharmony_ci<p>The <code>node:trace_events</code> module provides a mechanism to centralize tracing 3121cb0ef41Sopenharmony_ciinformation generated by V8, Node.js core, and userspace code.</p> 3131cb0ef41Sopenharmony_ci<p>Tracing can be enabled with the <code>--trace-event-categories</code> command-line flag 3141cb0ef41Sopenharmony_cior by using the <code>node:trace_events</code> module. The <code>--trace-event-categories</code> flag 3151cb0ef41Sopenharmony_ciaccepts a list of comma-separated category names.</p> 3161cb0ef41Sopenharmony_ci<p>The available categories are:</p> 3171cb0ef41Sopenharmony_ci<ul> 3181cb0ef41Sopenharmony_ci<li><code>node</code>: An empty placeholder.</li> 3191cb0ef41Sopenharmony_ci<li><code>node.async_hooks</code>: Enables capture of detailed <a href="async_hooks.html"><code>async_hooks</code></a> trace data. 3201cb0ef41Sopenharmony_ciThe <a href="async_hooks.html"><code>async_hooks</code></a> events have a unique <code>asyncId</code> and a special <code>triggerId</code> 3211cb0ef41Sopenharmony_ci<code>triggerAsyncId</code> property.</li> 3221cb0ef41Sopenharmony_ci<li><code>node.bootstrap</code>: Enables capture of Node.js bootstrap milestones.</li> 3231cb0ef41Sopenharmony_ci<li><code>node.console</code>: Enables capture of <code>console.time()</code> and <code>console.count()</code> 3241cb0ef41Sopenharmony_cioutput.</li> 3251cb0ef41Sopenharmony_ci<li><code>node.threadpoolwork.sync</code>: Enables capture of trace data for threadpool 3261cb0ef41Sopenharmony_cisynchronous operations, such as <code>blob</code>, <code>zlib</code>, <code>crypto</code> and <code>node_api</code>.</li> 3271cb0ef41Sopenharmony_ci<li><code>node.threadpoolwork.async</code>: Enables capture of trace data for threadpool 3281cb0ef41Sopenharmony_ciasynchronous operations, such as <code>blob</code>, <code>zlib</code>, <code>crypto</code> and <code>node_api</code>.</li> 3291cb0ef41Sopenharmony_ci<li><code>node.dns.native</code>: Enables capture of trace data for DNS queries.</li> 3301cb0ef41Sopenharmony_ci<li><code>node.net.native</code>: Enables capture of trace data for network.</li> 3311cb0ef41Sopenharmony_ci<li><code>node.environment</code>: Enables capture of Node.js Environment milestones.</li> 3321cb0ef41Sopenharmony_ci<li><code>node.fs.sync</code>: Enables capture of trace data for file system sync methods.</li> 3331cb0ef41Sopenharmony_ci<li><code>node.fs_dir.sync</code>: Enables capture of trace data for file system sync 3341cb0ef41Sopenharmony_cidirectory methods.</li> 3351cb0ef41Sopenharmony_ci<li><code>node.fs.async</code>: Enables capture of trace data for file system async methods.</li> 3361cb0ef41Sopenharmony_ci<li><code>node.fs_dir.async</code>: Enables capture of trace data for file system async 3371cb0ef41Sopenharmony_cidirectory methods.</li> 3381cb0ef41Sopenharmony_ci<li><code>node.perf</code>: Enables capture of <a href="perf_hooks.html">Performance API</a> measurements. 3391cb0ef41Sopenharmony_ci<ul> 3401cb0ef41Sopenharmony_ci<li><code>node.perf.usertiming</code>: Enables capture of only Performance API User Timing 3411cb0ef41Sopenharmony_cimeasures and marks.</li> 3421cb0ef41Sopenharmony_ci<li><code>node.perf.timerify</code>: Enables capture of only Performance API timerify 3431cb0ef41Sopenharmony_cimeasurements.</li> 3441cb0ef41Sopenharmony_ci</ul> 3451cb0ef41Sopenharmony_ci</li> 3461cb0ef41Sopenharmony_ci<li><code>node.promises.rejections</code>: Enables capture of trace data tracking the number 3471cb0ef41Sopenharmony_ciof unhandled Promise rejections and handled-after-rejections.</li> 3481cb0ef41Sopenharmony_ci<li><code>node.vm.script</code>: Enables capture of trace data for the <code>node:vm</code> module's 3491cb0ef41Sopenharmony_ci<code>runInNewContext()</code>, <code>runInContext()</code>, and <code>runInThisContext()</code> methods.</li> 3501cb0ef41Sopenharmony_ci<li><code>v8</code>: The <a href="v8.html">V8</a> events are GC, compiling, and execution related.</li> 3511cb0ef41Sopenharmony_ci<li><code>node.http</code>: Enables capture of trace data for http request / response.</li> 3521cb0ef41Sopenharmony_ci</ul> 3531cb0ef41Sopenharmony_ci<p>By default the <code>node</code>, <code>node.async_hooks</code>, and <code>v8</code> categories are enabled.</p> 3541cb0ef41Sopenharmony_ci<pre><code class="language-bash">node --trace-event-categories v8,node,node.async_hooks server.js</code> <button class="copy-button">copy</button></pre> 3551cb0ef41Sopenharmony_ci<p>Prior versions of Node.js required the use of the <code>--trace-events-enabled</code> 3561cb0ef41Sopenharmony_ciflag to enable trace events. This requirement has been removed. However, the 3571cb0ef41Sopenharmony_ci<code>--trace-events-enabled</code> flag <em>may</em> still be used and will enable the 3581cb0ef41Sopenharmony_ci<code>node</code>, <code>node.async_hooks</code>, and <code>v8</code> trace event categories by default.</p> 3591cb0ef41Sopenharmony_ci<pre><code class="language-bash">node --trace-events-enabled 3601cb0ef41Sopenharmony_ci 3611cb0ef41Sopenharmony_ci<span class="hljs-comment"># is equivalent to</span> 3621cb0ef41Sopenharmony_ci 3631cb0ef41Sopenharmony_cinode --trace-event-categories v8,node,node.async_hooks</code> <button class="copy-button">copy</button></pre> 3641cb0ef41Sopenharmony_ci<p>Alternatively, trace events may be enabled using the <code>node:trace_events</code> module:</p> 3651cb0ef41Sopenharmony_ci<pre><code class="language-js"><span class="hljs-keyword">const</span> trace_events = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:trace_events'</span>); 3661cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> tracing = trace_events.<span class="hljs-title function_">createTracing</span>({ <span class="hljs-attr">categories</span>: [<span class="hljs-string">'node.perf'</span>] }); 3671cb0ef41Sopenharmony_citracing.<span class="hljs-title function_">enable</span>(); <span class="hljs-comment">// Enable trace event capture for the 'node.perf' category</span> 3681cb0ef41Sopenharmony_ci 3691cb0ef41Sopenharmony_ci<span class="hljs-comment">// do work</span> 3701cb0ef41Sopenharmony_ci 3711cb0ef41Sopenharmony_citracing.<span class="hljs-title function_">disable</span>(); <span class="hljs-comment">// Disable trace event capture for the 'node.perf' category</span></code> <button class="copy-button">copy</button></pre> 3721cb0ef41Sopenharmony_ci<p>Running Node.js with tracing enabled will produce log files that can be opened 3731cb0ef41Sopenharmony_ciin the <a href="https://www.chromium.org/developers/how-tos/trace-event-profiling-tool"><code>chrome://tracing</code></a> 3741cb0ef41Sopenharmony_citab of Chrome.</p> 3751cb0ef41Sopenharmony_ci<p>The logging file is by default called <code>node_trace.${rotation}.log</code>, where 3761cb0ef41Sopenharmony_ci<code>${rotation}</code> is an incrementing log-rotation id. The filepath pattern can 3771cb0ef41Sopenharmony_cibe specified with <code>--trace-event-file-pattern</code> that accepts a template 3781cb0ef41Sopenharmony_cistring that supports <code>${rotation}</code> and <code>${pid}</code>:</p> 3791cb0ef41Sopenharmony_ci<pre><code class="language-bash">node --trace-event-categories v8 --trace-event-file-pattern <span class="hljs-string">'${pid}-${rotation}.log'</span> server.js</code> <button class="copy-button">copy</button></pre> 3801cb0ef41Sopenharmony_ci<p>To guarantee that the log file is properly generated after signal events like 3811cb0ef41Sopenharmony_ci<code>SIGINT</code>, <code>SIGTERM</code>, or <code>SIGBREAK</code>, make sure to have the appropriate handlers 3821cb0ef41Sopenharmony_ciin your code, such as:</p> 3831cb0ef41Sopenharmony_ci<pre><code class="language-js">process.<span class="hljs-title function_">on</span>(<span class="hljs-string">'SIGINT'</span>, <span class="hljs-keyword">function</span> <span class="hljs-title function_">onSigint</span>(<span class="hljs-params"></span>) { 3841cb0ef41Sopenharmony_ci <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">info</span>(<span class="hljs-string">'Received SIGINT.'</span>); 3851cb0ef41Sopenharmony_ci process.<span class="hljs-title function_">exit</span>(<span class="hljs-number">130</span>); <span class="hljs-comment">// Or applicable exit code depending on OS and signal</span> 3861cb0ef41Sopenharmony_ci});</code> <button class="copy-button">copy</button></pre> 3871cb0ef41Sopenharmony_ci<p>The tracing system uses the same time source 3881cb0ef41Sopenharmony_cias the one used by <code>process.hrtime()</code>. 3891cb0ef41Sopenharmony_ciHowever the trace-event timestamps are expressed in microseconds, 3901cb0ef41Sopenharmony_ciunlike <code>process.hrtime()</code> which returns nanoseconds.</p> 3911cb0ef41Sopenharmony_ci<p>The features from this module are not available in <a href="worker_threads.html#class-worker"><code>Worker</code></a> threads.</p> 3921cb0ef41Sopenharmony_ci<section><h3>The <code>node:trace_events</code> module<span><a class="mark" href="#the-nodetrace_events-module" id="the-nodetrace_events-module">#</a></span><a aria-hidden="true" class="legacy" id="tracing_the_node_trace_events_module"></a></h3> 3931cb0ef41Sopenharmony_ci<div class="api_metadata"> 3941cb0ef41Sopenharmony_ci<span>Added in: v10.0.0</span> 3951cb0ef41Sopenharmony_ci</div> 3961cb0ef41Sopenharmony_ci<h4><code>Tracing</code> object<span><a class="mark" href="#tracing-object" id="tracing-object">#</a></span><a aria-hidden="true" class="legacy" id="tracing_tracing_object"></a></h4> 3971cb0ef41Sopenharmony_ci<div class="api_metadata"> 3981cb0ef41Sopenharmony_ci<span>Added in: v10.0.0</span> 3991cb0ef41Sopenharmony_ci</div> 4001cb0ef41Sopenharmony_ci<p>The <code>Tracing</code> object is used to enable or disable tracing for sets of 4011cb0ef41Sopenharmony_cicategories. Instances are created using the <code>trace_events.createTracing()</code> 4021cb0ef41Sopenharmony_cimethod.</p> 4031cb0ef41Sopenharmony_ci<p>When created, the <code>Tracing</code> object is disabled. Calling the 4041cb0ef41Sopenharmony_ci<code>tracing.enable()</code> method adds the categories to the set of enabled trace event 4051cb0ef41Sopenharmony_cicategories. Calling <code>tracing.disable()</code> will remove the categories from the 4061cb0ef41Sopenharmony_ciset of enabled trace event categories.</p> 4071cb0ef41Sopenharmony_ci<h5><code>tracing.categories</code><span><a class="mark" href="#tracingcategories" id="tracingcategories">#</a></span><a aria-hidden="true" class="legacy" id="tracing_tracing_categories"></a></h5> 4081cb0ef41Sopenharmony_ci<div class="api_metadata"> 4091cb0ef41Sopenharmony_ci<span>Added in: v10.0.0</span> 4101cb0ef41Sopenharmony_ci</div> 4111cb0ef41Sopenharmony_ci<ul> 4121cb0ef41Sopenharmony_ci<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> 4131cb0ef41Sopenharmony_ci</ul> 4141cb0ef41Sopenharmony_ci<p>A comma-separated list of the trace event categories covered by this 4151cb0ef41Sopenharmony_ci<code>Tracing</code> object.</p> 4161cb0ef41Sopenharmony_ci<h5><code>tracing.disable()</code><span><a class="mark" href="#tracingdisable" id="tracingdisable">#</a></span><a aria-hidden="true" class="legacy" id="tracing_tracing_disable"></a></h5> 4171cb0ef41Sopenharmony_ci<div class="api_metadata"> 4181cb0ef41Sopenharmony_ci<span>Added in: v10.0.0</span> 4191cb0ef41Sopenharmony_ci</div> 4201cb0ef41Sopenharmony_ci<p>Disables this <code>Tracing</code> object.</p> 4211cb0ef41Sopenharmony_ci<p>Only trace event categories <em>not</em> covered by other enabled <code>Tracing</code> objects 4221cb0ef41Sopenharmony_ciand <em>not</em> specified by the <code>--trace-event-categories</code> flag will be disabled.</p> 4231cb0ef41Sopenharmony_ci<pre><code class="language-js"><span class="hljs-keyword">const</span> trace_events = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:trace_events'</span>); 4241cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> t1 = trace_events.<span class="hljs-title function_">createTracing</span>({ <span class="hljs-attr">categories</span>: [<span class="hljs-string">'node'</span>, <span class="hljs-string">'v8'</span>] }); 4251cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> t2 = trace_events.<span class="hljs-title function_">createTracing</span>({ <span class="hljs-attr">categories</span>: [<span class="hljs-string">'node.perf'</span>, <span class="hljs-string">'node'</span>] }); 4261cb0ef41Sopenharmony_cit1.<span class="hljs-title function_">enable</span>(); 4271cb0ef41Sopenharmony_cit2.<span class="hljs-title function_">enable</span>(); 4281cb0ef41Sopenharmony_ci 4291cb0ef41Sopenharmony_ci<span class="hljs-comment">// Prints 'node,node.perf,v8'</span> 4301cb0ef41Sopenharmony_ci<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(trace_events.<span class="hljs-title function_">getEnabledCategories</span>()); 4311cb0ef41Sopenharmony_ci 4321cb0ef41Sopenharmony_cit2.<span class="hljs-title function_">disable</span>(); <span class="hljs-comment">// Will only disable emission of the 'node.perf' category</span> 4331cb0ef41Sopenharmony_ci 4341cb0ef41Sopenharmony_ci<span class="hljs-comment">// Prints 'node,v8'</span> 4351cb0ef41Sopenharmony_ci<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(trace_events.<span class="hljs-title function_">getEnabledCategories</span>());</code> <button class="copy-button">copy</button></pre> 4361cb0ef41Sopenharmony_ci<h5><code>tracing.enable()</code><span><a class="mark" href="#tracingenable" id="tracingenable">#</a></span><a aria-hidden="true" class="legacy" id="tracing_tracing_enable"></a></h5> 4371cb0ef41Sopenharmony_ci<div class="api_metadata"> 4381cb0ef41Sopenharmony_ci<span>Added in: v10.0.0</span> 4391cb0ef41Sopenharmony_ci</div> 4401cb0ef41Sopenharmony_ci<p>Enables this <code>Tracing</code> object for the set of categories covered by the 4411cb0ef41Sopenharmony_ci<code>Tracing</code> object.</p> 4421cb0ef41Sopenharmony_ci<h5><code>tracing.enabled</code><span><a class="mark" href="#tracingenabled" id="tracingenabled">#</a></span><a aria-hidden="true" class="legacy" id="tracing_tracing_enabled"></a></h5> 4431cb0ef41Sopenharmony_ci<div class="api_metadata"> 4441cb0ef41Sopenharmony_ci<span>Added in: v10.0.0</span> 4451cb0ef41Sopenharmony_ci</div> 4461cb0ef41Sopenharmony_ci<ul> 4471cb0ef41Sopenharmony_ci<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> <code>true</code> only if the <code>Tracing</code> object has been enabled.</li> 4481cb0ef41Sopenharmony_ci</ul> 4491cb0ef41Sopenharmony_ci<h4><code>trace_events.createTracing(options)</code><span><a class="mark" href="#trace_eventscreatetracingoptions" id="trace_eventscreatetracingoptions">#</a></span><a aria-hidden="true" class="legacy" id="tracing_trace_events_createtracing_options"></a></h4> 4501cb0ef41Sopenharmony_ci<div class="api_metadata"> 4511cb0ef41Sopenharmony_ci<span>Added in: v10.0.0</span> 4521cb0ef41Sopenharmony_ci</div> 4531cb0ef41Sopenharmony_ci<ul> 4541cb0ef41Sopenharmony_ci<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> 4551cb0ef41Sopenharmony_ci<ul> 4561cb0ef41Sopenharmony_ci<li><code>categories</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string[]></a> An array of trace category names. Values included 4571cb0ef41Sopenharmony_ciin the array are coerced to a string when possible. An error will be 4581cb0ef41Sopenharmony_cithrown if the value cannot be coerced.</li> 4591cb0ef41Sopenharmony_ci</ul> 4601cb0ef41Sopenharmony_ci</li> 4611cb0ef41Sopenharmony_ci<li>Returns: <a href="tracing.html#tracing-object" class="type"><Tracing></a>.</li> 4621cb0ef41Sopenharmony_ci</ul> 4631cb0ef41Sopenharmony_ci<p>Creates and returns a <code>Tracing</code> object for the given set of <code>categories</code>.</p> 4641cb0ef41Sopenharmony_ci<pre><code class="language-js"><span class="hljs-keyword">const</span> trace_events = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:trace_events'</span>); 4651cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> categories = [<span class="hljs-string">'node.perf'</span>, <span class="hljs-string">'node.async_hooks'</span>]; 4661cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> tracing = trace_events.<span class="hljs-title function_">createTracing</span>({ categories }); 4671cb0ef41Sopenharmony_citracing.<span class="hljs-title function_">enable</span>(); 4681cb0ef41Sopenharmony_ci<span class="hljs-comment">// do stuff</span> 4691cb0ef41Sopenharmony_citracing.<span class="hljs-title function_">disable</span>();</code> <button class="copy-button">copy</button></pre> 4701cb0ef41Sopenharmony_ci<h4><code>trace_events.getEnabledCategories()</code><span><a class="mark" href="#trace_eventsgetenabledcategories" id="trace_eventsgetenabledcategories">#</a></span><a aria-hidden="true" class="legacy" id="tracing_trace_events_getenabledcategories"></a></h4> 4711cb0ef41Sopenharmony_ci<div class="api_metadata"> 4721cb0ef41Sopenharmony_ci<span>Added in: v10.0.0</span> 4731cb0ef41Sopenharmony_ci</div> 4741cb0ef41Sopenharmony_ci<ul> 4751cb0ef41Sopenharmony_ci<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> 4761cb0ef41Sopenharmony_ci</ul> 4771cb0ef41Sopenharmony_ci<p>Returns a comma-separated list of all currently-enabled trace event 4781cb0ef41Sopenharmony_cicategories. The current set of enabled trace event categories is determined 4791cb0ef41Sopenharmony_ciby the <em>union</em> of all currently-enabled <code>Tracing</code> objects and any categories 4801cb0ef41Sopenharmony_cienabled using the <code>--trace-event-categories</code> flag.</p> 4811cb0ef41Sopenharmony_ci<p>Given the file <code>test.js</code> below, the command 4821cb0ef41Sopenharmony_ci<code>node --trace-event-categories node.perf test.js</code> will print 4831cb0ef41Sopenharmony_ci<code>'node.async_hooks,node.perf'</code> to the console.</p> 4841cb0ef41Sopenharmony_ci<pre><code class="language-js"><span class="hljs-keyword">const</span> trace_events = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:trace_events'</span>); 4851cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> t1 = trace_events.<span class="hljs-title function_">createTracing</span>({ <span class="hljs-attr">categories</span>: [<span class="hljs-string">'node.async_hooks'</span>] }); 4861cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> t2 = trace_events.<span class="hljs-title function_">createTracing</span>({ <span class="hljs-attr">categories</span>: [<span class="hljs-string">'node.perf'</span>] }); 4871cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> t3 = trace_events.<span class="hljs-title function_">createTracing</span>({ <span class="hljs-attr">categories</span>: [<span class="hljs-string">'v8'</span>] }); 4881cb0ef41Sopenharmony_ci 4891cb0ef41Sopenharmony_cit1.<span class="hljs-title function_">enable</span>(); 4901cb0ef41Sopenharmony_cit2.<span class="hljs-title function_">enable</span>(); 4911cb0ef41Sopenharmony_ci 4921cb0ef41Sopenharmony_ci<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(trace_events.<span class="hljs-title function_">getEnabledCategories</span>());</code> <button class="copy-button">copy</button></pre> 4931cb0ef41Sopenharmony_ci</section><section><h3>Examples<span><a class="mark" href="#examples" id="examples">#</a></span><a aria-hidden="true" class="legacy" id="tracing_examples"></a></h3> 4941cb0ef41Sopenharmony_ci<h4>Collect trace events data by inspector<span><a class="mark" href="#collect-trace-events-data-by-inspector" id="collect-trace-events-data-by-inspector">#</a></span><a aria-hidden="true" class="legacy" id="tracing_collect_trace_events_data_by_inspector"></a></h4> 4951cb0ef41Sopenharmony_ci<pre><code class="language-js"><span class="hljs-meta">'use strict'</span>; 4961cb0ef41Sopenharmony_ci 4971cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> { <span class="hljs-title class_">Session</span> } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'inspector'</span>); 4981cb0ef41Sopenharmony_ci<span class="hljs-keyword">const</span> session = <span class="hljs-keyword">new</span> <span class="hljs-title class_">Session</span>(); 4991cb0ef41Sopenharmony_cisession.<span class="hljs-title function_">connect</span>(); 5001cb0ef41Sopenharmony_ci 5011cb0ef41Sopenharmony_ci<span class="hljs-keyword">function</span> <span class="hljs-title function_">post</span>(<span class="hljs-params">message, data</span>) { 5021cb0ef41Sopenharmony_ci <span class="hljs-keyword">return</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">Promise</span>(<span class="hljs-function">(<span class="hljs-params">resolve, reject</span>) =></span> { 5031cb0ef41Sopenharmony_ci session.<span class="hljs-title function_">post</span>(message, data, <span class="hljs-function">(<span class="hljs-params">err, result</span>) =></span> { 5041cb0ef41Sopenharmony_ci <span class="hljs-keyword">if</span> (err) 5051cb0ef41Sopenharmony_ci <span class="hljs-title function_">reject</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Error</span>(<span class="hljs-title class_">JSON</span>.<span class="hljs-title function_">stringify</span>(err))); 5061cb0ef41Sopenharmony_ci <span class="hljs-keyword">else</span> 5071cb0ef41Sopenharmony_ci <span class="hljs-title function_">resolve</span>(result); 5081cb0ef41Sopenharmony_ci }); 5091cb0ef41Sopenharmony_ci }); 5101cb0ef41Sopenharmony_ci} 5111cb0ef41Sopenharmony_ci 5121cb0ef41Sopenharmony_ci<span class="hljs-keyword">async</span> <span class="hljs-keyword">function</span> <span class="hljs-title function_">collect</span>(<span class="hljs-params"></span>) { 5131cb0ef41Sopenharmony_ci <span class="hljs-keyword">const</span> data = []; 5141cb0ef41Sopenharmony_ci session.<span class="hljs-title function_">on</span>(<span class="hljs-string">'NodeTracing.dataCollected'</span>, <span class="hljs-function">(<span class="hljs-params">chunk</span>) =></span> data.<span class="hljs-title function_">push</span>(chunk)); 5151cb0ef41Sopenharmony_ci session.<span class="hljs-title function_">on</span>(<span class="hljs-string">'NodeTracing.tracingComplete'</span>, <span class="hljs-function">() =></span> { 5161cb0ef41Sopenharmony_ci <span class="hljs-comment">// done</span> 5171cb0ef41Sopenharmony_ci }); 5181cb0ef41Sopenharmony_ci <span class="hljs-keyword">const</span> traceConfig = { <span class="hljs-attr">includedCategories</span>: [<span class="hljs-string">'v8'</span>] }; 5191cb0ef41Sopenharmony_ci <span class="hljs-keyword">await</span> <span class="hljs-title function_">post</span>(<span class="hljs-string">'NodeTracing.start'</span>, { traceConfig }); 5201cb0ef41Sopenharmony_ci <span class="hljs-comment">// do something</span> 5211cb0ef41Sopenharmony_ci <span class="hljs-built_in">setTimeout</span>(<span class="hljs-function">() =></span> { 5221cb0ef41Sopenharmony_ci <span class="hljs-title function_">post</span>(<span class="hljs-string">'NodeTracing.stop'</span>).<span class="hljs-title function_">then</span>(<span class="hljs-function">() =></span> { 5231cb0ef41Sopenharmony_ci session.<span class="hljs-title function_">disconnect</span>(); 5241cb0ef41Sopenharmony_ci <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(data); 5251cb0ef41Sopenharmony_ci }); 5261cb0ef41Sopenharmony_ci }, <span class="hljs-number">1000</span>); 5271cb0ef41Sopenharmony_ci} 5281cb0ef41Sopenharmony_ci 5291cb0ef41Sopenharmony_ci<span class="hljs-title function_">collect</span>();</code> <button class="copy-button">copy</button></pre></section> 5301cb0ef41Sopenharmony_ci <!-- API END --> 5311cb0ef41Sopenharmony_ci </div> 5321cb0ef41Sopenharmony_ci </div> 5331cb0ef41Sopenharmony_ci </div> 5341cb0ef41Sopenharmony_ci</body> 5351cb0ef41Sopenharmony_ci</html> 536