parentIds in NextTickWrap?

[Jeff-Lewis]

Hi, I'm experimenting with creating a version of CLS that uses async-hook and AsyncWrap instead of the older AsyncListener and it appears that it very rarely sees parentIds in the init hook.

Is this b/c of NextTickerWrap doesn't pass them? Is there an alternate way to wrap nextTick to include it?

[AndreasMadsen]

The parentId for NextTickerWrap is supposed to be null. In the final version of AsyncWrap that will also be the case.

This is because parentId is only set when a handle was directly created as a result of a another handle. Most popular example is a TCP server (parent) creating a TCP socket (child). The much more normal case is that some JavaScript code invoked for example nextTick and that way created a handle object. In this case the handle was created from a callback execution and not another handle.

The standard pattern for tracking the parent is:

• track the handle id (currentId) for the currently executing callback using the pre and post hooks.
• In the init hook use parent = parentId === null ? currentId : parentId.

example: https://github.com/AndreasMadsen/trace/blob/master/trace.js#L49 documentation: https://github.com/nodejs/diagnostics/tree/master/tracing/AsyncWrap#parentuid