Why Node.js Crashes When being Closed?


Some Javet users experience segfaults when using the Node.js mode. The segfaults occur when NodeRuntime is being closed. E.g. issue #20 and issue #82.

Root Cause

The root cause is Node.js event loop is activated when Node.js is exiting. Let's see how NodeRuntime.close() works behind the scenes.

  1. Close all Node.js modules

  2. Close all reference objects

  3. Close all callback context objects

  4. Close all V8 modules

  5. Hand over the control to Node.js exiting process

If the application registers interceptors, those interceptors will be closed at step 3. However, the corresponding JavaScript objects hasn't been recycled yet. So, at step 5, Node.js activates the event loop and async objects will get resolved or rejected. The callbacks land Javet which is not able to handle because the callback context objects are gone. That leads to memory corruption and segfaults.

Can Javet address that? Yes, but that implies hacking Node.js event loop. People choose Javet Node.js mode mostly because it is a genuine Node.js. So, no, Javet does not perform such hack.


Well, how to prevent that from happening? In fact, knowing how Javet works and following the Javet way, that won't happen.

Event unhandledRejection

Node.js provides a standard solution. Application can listen to event unhandledRejection to prevent that event from hitting Javet so that the segfaults will not take place.

import process from 'process';
process.on('unhandledRejection', (reason, promise) => {
  // Do whatever you want to do


Application may call NodeRuntime.await() before closing the NodeRuntime. This call explicitly tells NodeRuntime to activate the event loop.


Application may call NodeRuntime.lowMemoryNotification() before closing the NodeRuntime. This call forces NodeRuntime to perform garbage collection. During the garbage collection, the callbacks can be safely handled by Javet without segfaults.