feat: improve signal handling with timeout and better POSIX compliance (#1705)

[harshcoder-harsh]

Description

Implements the signal handling improvements proposed in #1705 for better POSIX compliance and systemd compatibility.

Changes

• ✨ SIGINT: Graceful shutdown with double Ctrl+C for force quit
• ✨ SIGTERM: Graceful shutdown with timeout, then SIGKILL (systemd-compatible)
• ✨ SIGQUIT: Immediate termination without cleanup
• ✨ SIGHUP: Default reload signal (replaces SIGUSR2)
• ⚙️ killTimeout: Configurable timeout for graceful shutdown (default: 10s)
• 📝 Documentation: Updated README with signal handling behavior and migration notes

Breaking Changes

⚠️ Default signal changed from SIGUSR2 to SIGHUP

Applications listening for SIGUSR2 should either:

• Update code to listen for SIGHUP (recommended), or
• Set --signal SIGUSR2 in nodemon configuration

Migration Example

// Old (still works with --signal SIGUSR2)
process.on('SIGUSR2', () => gracefulShutdown());

// New (recommended)
process.on('SIGHUP', () => gracefulShutdown());

Implementation Details

New killWithTimeout() Function

Added a new function that implements graceful shutdown with timeout-based escalation:

• Sends initial signal to child process
• Waits for configurable timeout
• Escalates to SIGKILL if child doesn't exit gracefully
• Properly manages event listeners and timers

Signal Handler Improvements

1. SIGINT (Ctrl+C):

   • First press: Graceful shutdown with timeout
   • Second press: Immediate SIGKILL
   • Provides user control over shutdown behavior

2. SIGTERM:

   • Passes signal to child
   • Waits for killTimeout
   • Escalates to SIGKILL if needed
   • Aligns with systemd's TimeoutStopSec

3. SIGQUIT (new):

   • Immediate SIGKILL
   • No cleanup
   • For emergency scenarios

4. SIGHUP (new):

   • Default reload signal
   • Replaces SIGUSR2 for better POSIX compliance

Testing

Manual testing has been performed for:

• ✅ SIGINT single press (graceful exit)
• ✅ SIGINT double press (force quit)
• ✅ SIGTERM with graceful exit
• ✅ SIGTERM with timeout escalation
• ✅ SIGQUIT immediate termination
• ✅ SIGHUP reload
• ✅ Custom killTimeout configuration

Backward Compatibility

Users can maintain the old behavior by explicitly setting signal: 'SIGUSR2' in their configuration:

nodemon --signal SIGUSR2 server.js

Or in nodemon.json:

{
  \"signal\": \"SIGUSR2\"
}

Related Issues

Fixes #1705
Related to #1667, #1661

Checklist

• Code follows the project's coding standards
• Documentation updated
• Breaking changes documented
• Commit messages follow conventional commits format
• Changes are backward compatible (with configuration)

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[remy]

There's no tests for this, but more worryingly, you've changed the defaults which would apply a massive blanket change.

I've not really read the AI generated PR description, happy if you want to write your own or summarise it down to a few lines with AI, but I do expect it to be fully tested.

One final point, there's no need for the details that were added to the readme, it's inconsistent with the project style.