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async_hooks: add getActiveResources (prototype)

Rodrigo Muino Tomonari requested to merge github/fork/Fishrock123/get-active-resources into master

Prototype of a new getActiveResources() API for async_hooks.

Returns an object map of { <id>: <resource> }, and differs slightly from getActiveHandles(). (The old API used to return the handle owner property for some reason.)

Currently, it works for all async_hooks resources except nextTick-s, which are probably not useful to expose in this way.

Reason being that nextTick-s almost always have no interesting information attached, and exist in async_hooks almost exclusively for continuation purposes. The same thing can pretty much be said for Immediate-s too, and I wouldn't be opposed to removing them from this.

As an alternative to not producing nextTicks, I think something along the lines of getActiveResources(async_type_mask) could be acceptable.

There are two primary reasons for why this might be useful compared to async_hooks, and why _getActiveHandles() is still useful today.

  1. Handle access. This bypasses the tricky problem of somehow storing a weak reference to handles so that you can access them up to destroy() but also not prevent GC.
  2. Performance. It is unnecessary to do tracking on each resource allocation, which requires boundary crossing for C++ resources on each call and also dealing with the way-too-plentiful nextTicks.

The root why of this is that some tools (such as N|Solid) like to have access to this kind of thing so we can inspect what kind of resources are active in a live application at any arbitrary point in time.

@nodejs/diagnostics @mike-kaufman @gpotter2

Supersedes https://github.com/nodejs/node/pull/21102 & probably also https://github.com/nodejs/node/pull/21313

Checklist
  • make -j4 test (UNIX), or vcbuild test (Windows) passes
  • tests and/or benchmarks are included
  • documentation is changed or added
  • commit message follows commit guidelines

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