Is it possible to hook into the moment a promise object is clean up?

[nabetti1720]

Related #1030
Related awslabs/llrt#947

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We are currently working on developing a nodejs compatible async_hooks module for LLRT.

We are getting close to completing the basic implementation, but I'm having trouble figuring out when to discard the ID information stored on the Rust side.

In the current implementation, the ID information created at the Init event is deleted when the resolve event occurs in the Promise Hook. However, if the events occur in the order before->resolve->after, the ID cannot be obtained in the after event.

I think there are a few solutions.

1. Give up on deleting the ID information (however, the longer the execution time, the more memory it consumes)

2. Receive an event when the Promise object is cleaned up. The promise object just before destruction is passed as an argument.

I think nodejs has a function for the latter as a destroy event, but is it possible to implement a similar event hook in quickjs? It would be great if there was a destroy version of a function like the already existing promise_rejection_tracker. It's something like promise_cleanup_tracker.

NOTE: For some reason, promise_rejection_tracker has not been exposed by rquickjs, so I'm not sure if it's a similar function...

[bnoordhuis]

Node's "destroy" hook is really just a GC reclamation callback. You can accomplish the same thing in quickjs with FinalizationRegistry.

[nabetti1720]

Thank you! I found that it can be used in the JavaScript layer (and also in the LLRT runtime).

The next issue is how to incorporate this into the Rust native implementation, but since this is outside the scope of this issue, I will close it. :)