v8: GetCpuProfiler is going away soon

[targos]

A new API was introduced in v8/v8@120b753.
The current API is deprecated in V8 6.4: v8/v8@8c5e2d7

Our usage:

node/src/env.cc

Lines 150 to 160 in 6aac05b

	void Environment::StartProfilerIdleNotifier() {
	uv_prepare_start(&idle_prepare_handle_, [](uv_prepare_t* handle) {
	Environment* env = ContainerOf(&Environment::idle_prepare_handle_, handle);
	env->isolate()->GetCpuProfiler()->SetIdle(true);
	});
	uv_check_start(&idle_check_handle_, [](uv_check_t* handle) {
	Environment* env = ContainerOf(&Environment::idle_check_handle_, handle);
	env->isolate()->GetCpuProfiler()->SetIdle(false);
	});
	}

[targos]

/cc @nodejs/v8

[ofrobots]

Hmm.. with the new API it seems that it should be possible to create multiple instances of the CPU profiler. Previously it was a singleton. This means that user-space modules could all use different profilers, and the idle notification above would stop working. Does this mean that Node needs to instantiate a singleton profiler and the ecosystem needs to change to start using that?

/cc @hashseed @fhinkel is my understanding correct?

[fhinkel]

Yes, with the old API, every isolate has one profiler assigned, created during Isolate::Init. With the new API, embedders can create multiple profilers.

Node could instantiate a singleton and provide that - or maybe we should invert dependencies: Addons can use as many profilers as they want, but they are responsible for registering for the IdleNotifier.

[bnoordhuis]

Node could instantiate a singleton and provide that - or maybe we should invert dependencies: Addons can use as many profilers as they want, but they are responsible for registering for the IdleNotifier.

I don't think we have to worry about that. We only use it to call CpuProfiler::SetIdle() and that's not even a proper CpuProfiler method (it updates v8::internal::Isolate::current_vm_state_.) Add-ons can create their own CpuProfiler instance.

I've opened #18534 with a simple fix.

[bnoordhuis]

And https://chromium-review.googlesource.com/c/v8/v8/+/900622 to discuss simplifying the API.