February 19th 2015

Agenda

What is trace_event?
- What is/are the primary use case(s)? (e.g. counters, perf tracing, async call continuation)
Status of: https://codereview.chromium.org/827993003
What tools are using it?
How would it be implemented?
- What features would io.js leverage?
- How would it affect existing subsystems?
- (currently test/ doesn't have an examples of how to use include/v8-tracing.h)
How does this feed into current API (i.e. AsyncWrap)?
What is left to do?
Why is the debugging port so slow in io.js and node.js 0.12?
- nodejs/node#877
Can/should tracing be exposed by iojs? via c++? via js?
- Anything in deps/v8/include/ can be accessed by native modules. So the question should be: What parts do we want to integrate into core?
Can we share async tracing facilities between iojs and chrome? (eg: Promises)
- see: window.fetch()

What is trace_event?

Created for client side analysis in Chrome
- Chrome is multi-threaded and needed additional information
1. Data format (JSON)
1. (C++) Is a way to place probes throughout the codebase
trace-event.h bottoms out in 3-4 C++ calls w/ specific purposes
- The macros turn into those few calls
To use v8-tracing.h, copy in tracing-event.h to have macro's use the internal API
2 parts
- Embedding API
- Control API (stop, start, get data, get categories)
Chrome dev tools protocol has JS APIs for control
Does not call at the moment a specific probe is called. Is less performance intrusive.

Status of V8 patch?