Exit Event Support

The exit event support utilities provide tools for handling worker thread termination across different JavaScript runtimes (Node.js, Deno, and Bun). These utilities help ensure consistent worker cleanup behavior regardless of the runtime environment.

API Reference

exitEventSupported

Tests whether the current runtime properly supports worker 'exit' events.

async function exitEventSupported(delay: number = 250): Promise<boolean>

Parameters

delay: (Optional) Maximum time in milliseconds to wait for the exit event. Defaults to 250ms.

Returns

Promise<boolean>: Resolves to true if exit events are properly supported, false otherwise.

exitKey

A special message key used as a signal for thread termination in environments where worker 'exit' events aren't natively supported.

const exitKey: string = '@@TerminateThread'

close

Safely closes a worker thread's parent port connection.

function close(parentPort: any): void

Parameters

parentPort: The parentPort from worker_threads module

Usage Examples

Runtime Detection

import { exitEventSupported } from '@renderdev/threadpool'

async function setupWorker() {
  const hasExitSupport = await exitEventSupported()

  if (hasExitSupport) {
    console.log('Using native exit events')
  } else {
    console.log('Using fallback message-based exit mechanism')
    process.env.USE_EXIT_FALLBACK = '1'
  }
}

Worker Script Cleanup

import { parentPort } from 'node:worker_threads'
import { close } from '@renderdev/threadpool'

// Your worker code here...

// When work is complete, safely close the worker
try {
  // Clean up resources...
  close(parentPort)
} catch (error) {
  console.error('Error during worker cleanup:', error)
  process.exit(1)
}

Manual Exit Event Handling

import { exitKey } from '@renderdev/threadpool'
import { Worker } from 'node:worker_threads'

const worker = new Worker('./worker.js')

// Listen for both standard exit and fallback exit
worker.on('exit', (code) => {
  console.log(`Worker exited with code ${code}`)
})

worker.on('message', (message) => {
  if (message === exitKey) {
    console.log('Received exit signal from worker')
    // Perform cleanup...
  }
})

Runtime Behavior

Node.js

Native exit events are fully supported
Fallback mechanism is not needed
close() simply calls parentPort.close()

Deno

Exit event support varies by version
Fallback mechanism used when needed
Both exit events and message-based exit may be active

Bun

Exit event support may be incomplete
Fallback mechanism is recommended
Message-based exit ensures reliable cleanup

Customizing Detection

You can customize the detection timeout based on your environment:

// Increase detection timeout for slower environments
const hasSupport = await exitEventSupported(1000) // 1 second timeout

// Quick check for development
const hasSupport = await exitEventSupported(50) // 50ms timeout

Internal Usage

These utilities are used internally by ThreadPool for:

Runtime environment detection
Worker pool cleanup coordination
Cross-runtime compatibility
Graceful worker termination

Best Practices

Always use close()

import { close } from '@renderdev/threadpool'

// Instead of parentPort.close()
close(parentPort)

Check Support on Startup

import { exitEventSupported } from '@renderdev/threadpool'

async function initialize() {
  const hasSupport = await exitEventSupported()
  // Configure your application accordingly
}

Handle Both Exit Types

import { exitKey } from '@renderdev/threadpool'

worker.on('exit', handleExit)
worker.on('message', (msg) => {
  if (msg === exitKey) handleExit()
})

API Reference​