Event Loop Block | Sentry for Next.js

Source URL: https://docs.sentry.io/platforms/javascript/guides/nextjs/configuration/integrations/event-loop-block

Event Loop Block | Sentry for Next.js

This integration only works in the Node.js runtime.

Import name: eventLoopBlockIntegration from @sentry/node-native

The eventLoopBlockIntegration can be used to monitor for blocked event loops in all threads of a Node.js application. Stack traces are automatically captured when blocking is detected.

Installation

npm install @sentry/node-native

Usage

If you instrument your application via the Node.js --import flag, Sentry will be started and this instrumentation will be automatically applied to all worker threads.

instrument.mjs

import { eventLoopBlockIntegration } from "@sentry/node-native";

Sentry.init({
  dsn: "__YOUR_DSN__",
  // Monitor event loop blocking for more than 500ms (stack traces automatically captured)
  integrations: [eventLoopBlockIntegration({ threshold: 500 })],
});

app.mjs

import { Worker } from "worker_threads";

const worker = new Worker(new URL("./worker.mjs", import.meta.url));

// This main thread will be monitored for blocked event loops

worker.mjs

// This worker thread will also be monitored for blocked event loops too

Start your application:

node --import instrument.mjs app.mjs

If a thread is blocked for more than the configured threshold, stack traces are automatically captured for all threads and sent to Sentry.

Configuration Options

You can pass a configuration object to the eventLoopBlockIntegration to customize the behavior:

interface ThreadBlockedIntegrationOptions {
  /**
   * Threshold in milliseconds to trigger an event.
   *
   * Defaults to 1000ms.
   */
  threshold: number;
  /**
   * Maximum number of blocked events to send per clock hour.
   *
   * Defaults to 1.
   */
  maxEventsPerHour: number;
  /**
   * Tags to include with blocked events.
   */
  staticTags: { [key: string]: Primitive };
}

Example Configuration

import { eventLoopBlockIntegration } from "@sentry/node-native";

Sentry.init({
  dsn: "__YOUR_DSN__",
  integrations: [
    eventLoopBlockIntegration({
      threshold: 500, // Trigger after 500ms of blocking (stack traces automatically captured)
      maxEventsPerHour: 5, // Maximum 5 events per hour
      staticTags: {
        component: "main-thread",
        environment: "production",
      },
    }),
  ],
});