• Investigate which DS can do this best (Probably, stack 😆 )
• Construct the event stack at a particular ts
• Generalise it for the entire duration of profiling

TBD : 2nd point, needs more discussion

The following fixes need to be made

1. Fix the RN Repo linking
2. Change the owner (TBD)
3. Publish the changes to npm 🎉

• Create a general interface for the general event
• Implement classes for all event types from the interface

First I followed https://reactnative.dev/docs/hermes/
then https://reactnative.dev/docs/profile-hermes

Recording a Hermes sampling profile seems to succeed
(hermes-profile-transformer is in my node-modules at version 0.0.6)
Then the command to convert and transfer the Hermes tracing profile fails as follows:

$ npx react-native profile-hermes ./dev
info Downloading a Hermes Sampling Profiler from your Android device...
info No filename is provided, pulling latest file
info File to be pulled: sampling-profiler-trace552874595700445033.cpuprofile
error Cannot read properties of undefined (reading 'pid').
TypeError: Cannot read properties of undefined (reading 'pid')
    at Function.collectProfileEvents (/Users/dev/app/node_modules/hermes-profile-transformer/dist/hermes-profile-transformer.cjs.development.js:315:28)
    at /Users/dev/app/node_modules/hermes-profile-transformer/dist/hermes-profile-transformer.cjs.development.js:517:43
    at async downloadProfile (/Users/dev/app/node_modules/@react-native-community/cli-hermes/build/profileHermes/downloadProfile.js:160:24)
    at async Object.profileHermes [as func] (/Users/dev/app/node_modules/@react-native-community/cli-hermes/build/profileHermes/index.js:28:5)
    at async Command.handleAction (/Users/dev/app/node_modules/@react-native-community/cli/build/index.js:192:9)
info Run CLI with --verbose flag for more details.

$ react-native info
info Fetching system and libraries information...
(node:25683) Warning: Accessing non-existent property 'padLevels' of module exports inside circular dependency
(Use `node --trace-warnings ...` to show where the warning was created)
System:
    OS: macOS 12.4
    CPU: (12) x64 Intel(R) Core(TM) i7-9750H CPU @ 2.60GHz
    Memory: 857.19 MB / 16.00 GB
    Shell: 5.1.16 - /usr/local/bin/bash
  Binaries:
    Node: 16.14.2 - /usr/local/bin/node
    Yarn: 1.22.15 - /usr/local/bin/yarn
    npm: 8.5.0 - /usr/local/bin/npm
    Watchman: Not Found
  Managers:
    CocoaPods: 1.11.3 - /usr/local/bin/pod
  SDKs:
    iOS SDK:
      Platforms: DriverKit 21.4, iOS 15.5, macOS 12.3, tvOS 15.4, watchOS 8.5
    Android SDK: Not Found // but it is present, API level 30
  IDEs:
    Android Studio: 2021.1 AI-211.7628.21.2111.8309675
    Xcode: 13.4.1/13F100 - /usr/bin/xcodebuild
  Languages:
    Java: 11.0.14.1 - /usr/bin/javac
  npmPackages:
    @react-native-community/cli: Not Found
    react: 17.0.2 => 17.0.2 
    react-native: 0.67.2 => 0.67.2 
    react-native-macos: Not Found
  npmGlobalPackages:
    *react-native*: Not Found

• Fix node version in the CI build

• Integrate the Lighthouse Profile Parser.

1. The Hermes profile needs to be converted into Profile Chunks
2. The Profile Chunks can then be passed to the CPUProfiler defined in Lighthouse to generate Chrome Supported B/E Duration Events.

This needs to be done so that the package can be used by React Native CLI.

Rather than index.bundle being the name of the file, we want the corresponding file name in the event name (Eg: __guard(http://10.0.2.2:8081/index.bundle?platform=android&dev=true&minify=false:2702:15) => __guard(fileName of this function)

EDIT:
one workaround is to use chrome://tracing to inspect profile

Hello, I'm trying to profile a react-native app, I followed the official documentation on how to pull and transform the Hermes tracing profile.

So once the profile is recorded I'm running this:

npx react-native profile-hermes \
  --sourcemap-path './android/app/build/intermediates/sourcemaps/react/debug/index.android.bundle.packager.map'\
  ~/Downloads

It outputs this:

warn Package expo-modules-core has been ignored because it contains invalid configuration. Reason: "dependency.platforms.ios" must be of type object
info Downloading a Hermes Sampling Profiler from your Android device...
info No filename is provided, pulling latest file
info File to be pulled: sampling-profiler-trace1250977739574747452.cpuprofile
success Successfully converted to Chrome tracing format and pulled the file to /Users/olivier.freyssinet/Downloads/sampling-profiler-trace1250977739574747452-converted.json

And here attached you can file the output .json. I don't know about the formatting but it seems to contain actual data that reflects what's going on in my app, so then it's just a matter of parsing it I guess.

So then I try to load it in the performance tab of Chrome Version 109.0.5414.119 (Official Build) (arm64)
It seems to be parsing the whole file but then nothing is displayed and I get the following error in the console (three times):

17:30:02.957 Failed to find browser main thread in trace, some timeline features may be unavailable
17:30:02.958 Failed to find browser main thread in trace, some timeline features may be unavailable
17:30:02.982 Failed to find browser main thread in trace, some timeline features may be unavailable

Another person who is trying on a Linux computer gets this slightly more explicit error:

Error parsing trace data: no TracingStartedInBrowser event found

Hermes version:

"hermes-engine": "0.11.0"

react-native info output

System:
    OS: macOS 12.5.1
    CPU: (10) arm64 Apple M1 Max
    Memory: 96.39 MB / 32.00 GB
    Shell: 5.8.1 - /bin/zsh
  Binaries:
    Node: 16.15.0 - /usr/local/bin/node
    Yarn: 1.22.18 - /opt/homebrew/bin/yarn
    npm: 8.5.5 - /usr/local/bin/npm
    Watchman: 2022.09.19.00 - /opt/homebrew/bin/watchman
  Managers:
    CocoaPods: 1.11.3 - /usr/local/bin/pod
  SDKs:
    iOS SDK:
      Platforms: DriverKit 22.2, iOS 16.2, macOS 13.1, tvOS 16.1, watchOS 9.1
    Android SDK:
      API Levels: 29, 30, 31, 32, 33
      Build Tools: 28.0.3, 30.0.2, 30.0.3, 31.0.0, 32.0.0, 32.1.0
      System Images: android-31 | Google APIs ARM 64 v8a, android-32 | Google APIs ARM 64 v8a, chromeos-67 | Chrome OS 67
      Android NDK: 22.1.7171670
  IDEs:
    Android Studio: 2021.1 AI-211.7628.21.2111.8309675
    Xcode: 14.2/14C18 - /usr/bin/xcodebuild
  Languages:
    Java: 11.0.15 - /usr/bin/javac
  npmPackages:
    @react-native-community/cli: ^7.0.1 => 7.0.4 
    react: ^17.0.2 => 17.0.2 
    react-native: 0.68.5 => 0.68.5 
    react-native-macos: Not Found
  npmGlobalPackages:
    *react-native*: Not Found

Thanks in advance for any help! 🙏

The Trace Event Format has listed down the various chrome events and how they are understood by the Chrome Profiler.

The Chrome Profiler consumes this profiling data in the JSON Array Format while the Hermes Profile is generated in the JSON Object Format. We might have made an oversight in assuming that the traceEvents generated by the Hermes Profiler are going to have phases assigned similar to Chrome Profiler, however this is not the case.

The phases in the case of the Hermes Profile need to be derived from the Samples and Stack Frames Properties in the Hermes Profile. This is where things are accumulated from lower level OS Kernels and we need to make sense of this data.

Reproduce steps:

1. Enable sampling profiler on android device (Xiaomi Redmi Go)
2. Disable it
3. Download .cpuprofile
4. Transform with transform script (without source maps)
5. Try upload to chrome dev performance tab
6. Got the error

Input: sampling-profiler-trace3882871943179202698.cpuprofile
Output (unzip): chrome-supported.json.zip

Transform script:

/**
 * Used to transform hermes profiler outputs to supported by chrome dev tools.
 * https://github.com/react-native-community/hermes-profile-transformer
 */

const transformer = require('hermes-profile-transformer').default
const { writeFileSync } = require('fs')

const hermesCpuProfilePath = 'sampling-profiler-trace3882871943179202698.cpuprofile'

transformer(
  // profile path is required
  hermesCpuProfilePath
  // source maps are optional
  // sourceMap,
  // sourceMapBundleFileName
)
  .then((events) => {
    // write converted trace to a file
    return writeFileSync('./chrome-supported.json', JSON.stringify(events, null, 2), 'utf-8')
  })
  .catch((err) => {
    console.log(err)
  })

The Trace Event Format has listed down the various chrome events and how they are understood by the Chrome Profiler.

The Chrome Profiler consumes this profiling data in the JSON Array Format while the Hermes Profile is generated in the JSON Object Format. We might have made an oversight in assuming that the traceEvents generated by the Hermes Profiler are going to have phases assigned similar to Chrome Profiler, however this is not the case.

The phases in the case of the Hermes Profile need to be derived from the Samples and Stack Frames Properties in the Hermes Profile. This is where things are accumulated from lower level OS Kernels and we need to make sense of this data.

• Investigate why stackFrames (particularly stackFrames with name App.js) don't show up
• Fix the convertToChromeSample method
• Fix the setNodePhase method

Question

I tried it out with my React Native app running on React Native 0.63.1 with Hermes enabled, but when I load the trace in Chrome Dev Tools, every item in the view is labeled as "anonymous". There are some details that list file names and line numbers specifically in the flame chart, and while the file names look like they could be correct, the line numbers make no sense when I look at the source. Additionally, the timing information doesn't make sense, as there are root level blocks in the flame graph that say they took ~250ms which is not possible as I'm using requestAnimationFrame to render graphics at 60fps.

Since it seems like it isn't really working, my question is whether there is a min version of React Native (or Hermes specifically) supported by hermes-profile-transformer. Should it work for the version of Hermes included in React Native 0.63.1?

• Duration Events
• Complete Events
• Metadata Events
• Sample Events
• Object Events
• ClockSync Events
• Async Events
• Context Events

when will ios support add because from react-native 0.0.64 Hermes has added in ios

Feature request

The migration of Duration events to Complete events would be extremely useful here, as they essentially capture the same information in half the file size.

Why it is needed

For more context, please read the Complete Events section of Trace Event Format Document. Theoretically, this should reduce the file size by a factor of 2 🎉

Possible implementation

Keeping track of current and last active nodes, we can clearly determine all the events that are starting and ending at a particular timestamp.

A way to implement this would be to add all the start events (along with their timestamp of starting) in a hashMap, and only add the chrome events object after they have completed (duration can be obtained by subtracting end/current and start timestamps)

• Setup Phase Types

Requirements

• Automatically convert TypeScript to JS on the fly
• Create a JS bundle to publish to NPM

Ideas

• Use TSDX

We need to test the following

• Correct profile output
• Correct intermediate profile chunk to be parsed by Lighthouse

The idea is to isolate similar events and assign phases to them after reviewing these similar events

• Instant Event
• Counter Event
• Flow Event
• Memory Dump Event
• Mark Event
• Linking ID Event

As discussed with @axemclion, we would want to have only three categories

• React Native + React + Metro - One category
• Keep the default categories obtained
• Introduce a third category for node_modules other than the ones introduced in 1