Scope of inspector/tracing agents

[addaleax]

• Subsystem: inspector, tracing

Currently, the inspector agent and a possible tracing writer are per-Environment on Node’s side. However, as far as I can tell, on the V8 side they are fundamentally per-Isolate and per-Platform, respectively.

So, my question for @nodejs/v8-inspector @nodejs/trace-events here is:

• Should we move the Inspector handle and CLI debug options from Environment to IsolateData?
• Should we move the tracing handle and corresponding CLI options to a global/per-process model?

[jasnell]

Yes, tracing should be global/per-Platform in the current implementation. Whether or not that makes sense long term I don't know. /cc @ofrobots

[eugeneo]

Inspector agent is per-"target" - i.e. workers have their own instance. Are there any cases when there are multiple isolates for one environment?

IMHO, inspector Agent does not need to know about CLI options at all.

[pavelfeldman]

@eugeneo, Tracing is global, Tracing domain on the root target should handle tracing for everything, including workers. There should be no tracing agents on the workers. Tracing started event should be propagated to all the isolates (workers) so that tracing controller singleton was capturing all the samples from all of them. This functionality would be typically implemented in the tracing controller with the Tracing domain being an interfacing shim sitting on top of it.

[addaleax]

Are there any cases when there are multiple isolates for one environment?

@eugeneo There can be multiple Environments for a single Isolate. Since currently inspector Agents and Environments are 1:1, I guess the question is, do multiple Agents per Isolate conflict with each other?

[pavelfeldman]

do multiple Agents per Isolate conflict with each other?

they don't in chrome, but it requires proper context goup management. @ak239 would know if we already do that in node.