worker,etw: only enable ETW on the main thread

[addaleax]

The Windows ETW code is not written to be compatible with multi-threading,
and in particular it relies on global state like a single static
uv_async_t. Adding that to multiple threads would corrupt the
corresponding loops' handle queues.

This addresses the flakiness of at least test-worker-exit-code and
very likely other flaky tests that relate to Worker threads on Windows as well.

(I've marked the less-easy-to-reproduce flaky tests as likely fixed -- we can still re-open the issues if it turns they are still problematic.)

Fixes: #25847
Fixes: #25702 (likely)
Fixes: #24005 (likely)
Fixes: #23873 (likely)

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes (probably)
• 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/2501/pipeline

[addaleax]

CI: https://ci.nodejs.org/job/node-test-pull-request/20553/ (:heavy_check_mark:)

[gireeshpunathil]

@addaleax - if the events are registered only by main thread (though this change) then the ETW event callbacks (etw_events_enable_callback) are also received in the main thread? If so, do we need another level of callback through the async (etw_events_change_async) ? can't we directly invoke v8 from the win32 callback itself?

[addaleax]

@gireeshpunathil I am unfamiliar with this code; however:

node/src/node_win32_etw_provider.cc

Lines 121 to 125 in 5506dcd

	// Call v8 to enable or disable code event callbacks.
	// Must be on default thread to do this.
	// Note: It is possible to call v8 from ETW thread, but then
	// event callbacks are received in the same thread. Attempts
	// to write ETW events in this thread will fail.

(To add context: That comment was written in 2012. I would definitely take it with a grain of salt – if calling V8 APIs from a different thread is what’s happening, it’s likely to not be allowed by V8.)

[addaleax]

Landed in 63ab542