Collect tracing data from Electron that may be loaded into the Chrome devtools

electron-trace.js

const TRACEOPTS = {
  categoryFilter: [
    '-*', 'devtools.timeline', 'disabled-by-default-devtools.timeline',
    'disabled-by-default-devtools.timeline.frame', 'toplevel', 'blink.console',
    'disabled-by-default-devtools.timeline.stack',
    'disabled-by-default-v8.cpu_profile', 'disabled-by-default-v8.cpu_profiler',
    'disabled-by-default-v8.cpu_profiler.hires'
  ].join(','),
  traceOptions: 'record-until-full',
  options: 'sampling-frequency=10000'
}

class Tracer {
  async start () {
    this.startMs = Date.now()
    await new Promise(resolve => {
      electron.contentTracing.startRecording(TRACEOPTS, resolve)
    })
  }

  async stop () {
    this.endMs = Date.now()
    await new Promise(resolve => {
      electron.contentTracing.stopRecording('', tracePath => {
        if (this.endMs - this.startMs < 10000) {
          fs.removeSync(tracePath)

          resolve()
          return
        }

        const traceData = JSON.parse(fs.readFileSync(tracePath, {encoding: 'utf8'}))
        const metadata = traceData.metadata
        const traceEventsByPid = new Map()
        for (const traceEvent of traceData.traceEvents) {
          let events = traceEventsByPid.get(traceEvent.pid)
          if (!events) {
            events = []
            traceEventsByPid.set(traceEvent.pid, events)
          }
          events.push(traceEvent)
        }

        for (const [pid, traceEvents] of traceEventsByPid.entries()) {
          const pidTracePath = path.resolve(`trace-${this.startMs}-${pid}.json`)
          fs.writeFileSync(pidTracePath, JSON.stringify({metadata, traceEvents}), {encoding: 'utf8'})
        }

        resolve()
      })
    })
  }
}