Print a "current stack/callback/promise dump" from a running program

[DanKaplanSES]

What is the problem this feature will solve?

Somewhere in my program I believe I have a Promise that never resolves/rejects, and it's difficult to troubleshoot without modifying the code:

1. I could add log statements everywhere
2. I could wrap every existing promise in a Promise.race([PromiseWithTimeout, OriginalPromise])
3. I could get v21+ and use --trace-promises to see if it prints enough information for me to figure out which promise is stuck.

While I haven't tried 3., it sounds extremely useful. That said, in a situation where the program hangs without error, I think a similar feature may be a better tool for the job: The ability to dump the current stack/callback/promises of a running program. As far as I know, this feature doesn't exist in node, but it does in other runtimes (see below).

For the original context of this feature request, see my StackOverflow post titled, How do you find the stack trace of a JavaScript Promise that never resolves?

What is the feature you are proposing to solve the problem?

In my SO post I mention that "Java has ways to see all the stack traces of all the threads of a program." [by running kill -3 <java_process_id>]. I'd like to request a similar feature in node.js.

What alternatives have you considered?

I've mentioned three alternatives in the list above.

[legendecas]

Promises will not lead to hanging processes. Instead, it is the active uv requests/handles that keep the process running. It is possible to inspect active uv handles with diagnostic reports, which can also be triggered with SIGUSR2 when the process is launched with the flag --report-on-signal.

[targos]

Promise tracking is expensive and cannot be done on-demand during runtime (it requires to install async_hooks before the promises are created).
I'm not sure it makes much sense to add something like that in core, it should be doable in userland with the async_hooks API.

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