Add July meeting notes

wg-meetings/2016-07-13.md

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+# Node.js Diagnostics WG Meeting
+
+- Date: 2016-07-13
+- YouTube: http://www.youtube.com/watch?v=BtZ6aFrD8gQ
+
+## Attendees
+
+- Josh Gavant (@joshgav)
+- Michael Dawson (@mhdawson)
+- Thomas Watson (@watson)
+- Andreas Madsen (@andreasmadsen)
+- Matt Loring (@matthewloring)
+- Ali Sheikh (@ofrobots)
+- Raymond Kang (@misterpoe)
+- Cristian Cavalli (@cristiancavalli)
+- Daniel Khan (@danielkhan)
+- Trevor Norris (@trevnorris)
+
+## Agenda
+
+- AsyncWrap - [[nodejs/node-eps#18](https://github.com/nodejs/node-eps/pull/18)]
+- Trace Controller [[nodejs/diagnostics#53](https://github.com/nodejs/diagnostics/issues/53)]
+- Inspector Protocol [[nodejs/node#7393](https://github.com/nodejs/node/issues/7393)]
+- APM Summit [[nodejs/diagnostics#58](https://github.com/nodejs/diagnostics/issues/58)
+
+## Minutes
+
+## AsyncWrap
+
+- [[nodejs/node-eps#18](https://github.com/nodejs/node-eps/pull/18)]
+- [[nodejs/diagnostics#29](https://github.com/nodejs/diagnostics/issues/29)]
+
+@trevnorris: Do not have ability to instrument promises and it doesn’t look promising.
+
+Follow [[nodejs/diagnostics#29](https://github.com/nodejs/diagnostics/issues/29)], create separate issues for specific items.
+
+**Questions**:
+
+- Do we need to deprecate `AsyncWrap::MakeCallback`? @trevnorris: eventually.
+- What about the duplication of `node::MakeCallback` and `AsyncWrap::MakeCallback`? @trevnorris: There will be less duplication but some is still needed.
+- User modules cannot currently be instrumented by AsyncWrap.
+- How will AsyncWrap be integrated in NaN's callback wrapper?
+- How will AsyncWrap be implemented in the in-progress ABI-stable API?
+
+**Next steps**:
+
+- One significant change remains to enable multiple listeners.
+- @trevnorris is working on a JS wrapper module for AsyncWrap to make it more usable for end users.
+
+
+## Tracing Controller
+
+- [[nodejs/diagnostics#53](https://github.com/nodejs/diagnostics/issues/53)]
+
+Some components will live in V8, some in Node. PR with V8 component: <https://codereview.chromium.org/2137013006/>
+
+Will provide interface for configuring trace collection and serialization format. Will also provide aggregation and filtering capabilities.
+
+Prototyped a Node-specific subclass of V8 component and able to get V8 traces. Added some trace points in `fs` to test.
+
+@joshgav: Will there be an interface for user modules (native or JS) to read and write traces?
+
+@ofrobots: Goal is to get basics in, then it’s up to Node.js to decide if/how to expose to users.
+
+@mattloring: Currently based on C++ macros and included directly in code.
+
+**Q**: What information is provided in a trace?
+
+**A**: CPU, TID, PID, timestamp. Follow-on work planned to allow alternate arguments. Also, some TRACE_EVENT macros accept additional metadata.
+
+**Q**: Where is output written to?
+
+**A**: Will provide a `TraceWriter` interface which users can derive from and write to file, stream, whatever.
+
+**Timeline**: V8 v5.4.
+
+**Next steps**:
+
+- Matt and Ali continue working on V8/Chromium implementation.
+- Add trace points throughout Node core codebase.
+- Define and implement interfaces for JS and native modules to read from and write to trace system.
+
+
+## Inspector
+
+[[nodejs/node#7393](https://github.com/nodejs/node/issues/7393)]
+
+@joshgav: Intent is to enable other engines to use same debugging protocol as V8 without having to implement V8's diagnostic APIs.
+
+Also need to update CLI debugger.
+
+Check `v8_inspector` tag in nodejs/node for needed contributions.
+
+
+## APM Summit
+
+[[nodejs/diagnostics#58](https://github.com/nodejs/diagnostics/issues/58)]
+
+
+@watson: At NodeConf Adventure discussed how APM providers are solving the same problem over and over again. Idea is a shared service in a module or part of core.
+
+Agenda would be:
+
+- Application-level traces especially for HTTP, DB requests (I/O). Currently requires ugly monkey-patching. AsyncWrap addresses some needs but not all. Key need is to keep a context across async boundaries.
+
+- Problem with ES modules because they can’t be monkey-patched.
+
+@joshgav: Can application-level traces be provided through the Tracing Controller?
+
+@ofrobots: TRACE_EVENT could be a source of information, but true need is to track async context.
+
+@watson: Can Trace Controller be used in production?
+
+@ofrobots: Yes, it’s designed for investigating perf issues, but it depends on number of events.
+
+@ofrobots: Think of Tracing Controller as “structural profiling” as opposed to "sampling profiling."
+
+Right now no user modules have been instrumented with TRACE_EVENT anyway. But eventually modules could be instrumented with same.
+
+@watson: Provide a standard API/format for tracing so all module authors could instrument their own code.
+
+@andreasmadsen: In what way does AsyncWrap not address this problem?
+
+@watson: example is postgres module, which maintains a pool of callbacks. Callbacks retain context in which pool was originally created [so AsyncWrap fails].
+
+@ofrobots: AsyncWrap helps with Node core, but the notion of a logical context doesn’t exist in JS.
+
+Zones proposal was also an attempt to solve this problem.
+
+**Next steps**:
+
+- Many won’t be at Node Summit, we’ll postpone to a later conference. @watson will create a Doodle.
+
+
+## Next Meeting
+
+- Early September.