report: do not use uv_default_loop() as fallback

[addaleax]

Not seeing an associated Environment is a rare condition anyway,
but using uv_default_loop() as a fallback is not thread-safe.

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• commit message follows commit guidelines

[nodejs-github-bot]

@addaleax build started: https://ci.nodejs.org/blue/organizations/jenkins/node-test-pull-request-lite-pipeline/detail/node-test-pull-request-lite-pipeline/2348/pipeline

[addaleax]

CI: https://ci.nodejs.org/job/node-test-pull-request/20271/

[richardlau]

Since the report is meant to aid diagnostics, is there any value in logging that env was null in the report?

[addaleax]

@richardlau I guess we could do that – do you have any suggestion on how to represent that?

[gireeshpunathil]

@addaleax :

Not seeing an associated Environment is a rare condition anyway,

IIRC, under fatalerror conditions (as registered to, detected and called back by v8) env was always null; either:

• somewhere on the line the env pointer is nullified by someone, or
• the fatalerror handler is invoked in such a scenario where Environment and Isolate are disassociated.

Something to investigate in future, but irrespective of that, this change looks good to me, for a clean and meaningful report.

[addaleax]

@gireeshpunathil I think the test that checks fatalerror conditions is OOM-based, so, in that case no Environment would be associated with the Isolate because the Isolate is running the garbage collector when it fails?

I think for other fatal errors (e.g. calling ToLocalChecked() on an empty MaybeLocal<>) that’s not the case:

$ ./node --experimental-report --diagnostic-report-on-fatalerror
> Object.defineProperty(Object.prototype, 'Serializer', { set() { throw new Error('BOOM'); } }) {}
> require('v8')
FATAL ERROR: v8::FromJust Maybe value is Nothing.
Writing Node.js report to file: report.20190123.145041.2475.001.json
Node.js report completed
[...]
$ grep -A5 libuv report.20190123.145041.2475.001.json "libuv": [
{
"type": "async",
"is_active": "1",
"is_referenced": "0",
"address": "93930778479248",

[gireeshpunathil]

@addaleax - thanks for the clarification, I wasn't aware of such fatalerror types.

[addaleax]

(If you’re wondering why I changed the commit message, it just occurred to me that the previous one is kind of ableist.)

CI: https://ci.nodejs.org/job/node-test-pull-request/20302/

[addaleax]

Resume CI: https://ci.nodejs.org/job/node-test-pull-request/20333/

[Trott]

CI: https://ci.nodejs.org/job/node-test-pull-request/20342/

[addaleax]

Landed in bb774b1