async_hooks: fix nested hooks mutation

[AndreasMadsen]

Checklist

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

Affected core subsystem(s)

async_hooks

In some cases restoreTmpHooks is called too early, this causes active_hooks_array to change during execution of the init hooks.

This depends on #14054

[AndreasMadsen]

CI: https://ci.nodejs.org/job/node-test-pull-request/9058/

[AndreasMadsen]

CI: https://ci.nodejs.org/job/node-test-pull-request/9059/

[addaleax]

You kept crypto here, was that intentional? If so, it probably needs a guard for skipping the test if appropriate

[AndreasMadsen]

That is from the blocking PR, I will rebase once that is fixed.

[refack]

-0.1

[refack]

I'm worried that doing reference counting is too fragile.
Why not replace the for either with a .forEach for with a for (const hook of Array.from(active_hooks_array))

[AndreasMadsen]

I'm worried that doing reference counting is too fragile.

Could you be more explicit?

edit: Just to avoid confusion, this is not a reference counting it is a depth counting.

Why not replace the for either with a .forEach

.forEach is not resistant to mutation.

const a = [1,2,3];
a.forEach(function (value) {
  process._rawDebug(value);
  a.pop();
});

prints 1 2.

with a for (const hook of Array.from(active_hooks_array))

Array copy is too slow. When async_hooks is enabled this is the hottest code path we have.

[refack]

Ack. I was sure .forEach iterated over a fixed array (it just ignores newly added elements)

[refack]

Just a 2 nits

[refack]

nit: Since we are going with depth counting, IMHO the decrement should be in a finally clause

[AndreasMadsen]

I guess, but there is no way to escape fatalError so the code will never be executed.

The try catch finally order is:

try {
  throw new Error();
} catch (e) {
  console.log('catch');
} finally {
  console.log('finally');
}

outputs catch finally.

[refack]

I guess, but there is no way to escape fatalError so the code will never be executed.

At the moment... If at some point we'll enable a fatalError trap this will break. Better to be explicit about these.
Reference/depth counting only works if it's ACID

[refack]

finally

[AndreasMadsen]

CI: https://ci.nodejs.org/job/node-test-pull-request/9092/

[trevnorris]

Thanks much. Especially for the additional code comment in init(). Have a non-blocking nit to change the processing_hooks code comment to explain that it's a depth counter.

[trevnorris]

Possibly change comment above from simply

Track whether a hook [...]

to something like

Use a counter to track [...] and prevent nested calls [...]

[AndreasMadsen]

Fixed the nit. I had to use some artistic freedom to fit in the "prevent nested calls" part. But the meaning should be the same.

CI: https://ci.nodejs.org/job/node-test-pull-request/9106/

[AndreasMadsen]

landed in f94fd0c

[trevnorris]

@AndreasMadsen Awesome. Thanks for adding the comment changes.