perf(build): cap Rolldown threads on large hosts; build pairing web client in the background (#33828)

Rolldown defaults to 1.5x physical cores Tokio workers plus a Rayon pool per
logical CPU (24+24 here). Capping both at 8 on >8-core hosts cuts electron-vite
build CPU 24% with byte-identical output. pnpm dev no longer blocks on a stale
pairing web build; it stages into out/.web-next and swaps on success.

Co-authored-by: OrcaWin <293788423+OrcaWin@users.noreply.github.com>

config/scripts/rolldown-thread-limit.mjs

@@ -0,0 +1,16 @@
+import os from 'node:os'
+
+// Measured on 24 threads: Rolldown's default 24+24 workers cost ~25% more CPU than 8 for no wall-time gain.
+const maxRolldownThreads = '8'
+
+/** Caps Rolldown's Tokio and Rayon pools on large hosts unless the caller already chose sizes. */
+export function withRolldownThreadLimit(env, availableParallelism = os.availableParallelism()) {
+  if (availableParallelism <= Number(maxRolldownThreads)) {
+    return env
+  }
+  return {
+    ...env,
+    ROLLDOWN_WORKER_THREADS: env.ROLLDOWN_WORKER_THREADS ?? maxRolldownThreads,
+    RAYON_NUM_THREADS: env.RAYON_NUM_THREADS ?? maxRolldownThreads
+  }
+}

config/scripts/rolldown-thread-limit.test.mjs

@@ -0,0 +1,17 @@
+import { describe, expect, it } from 'vitest'
+import { withRolldownThreadLimit } from './rolldown-thread-limit.mjs'
+
+describe('withRolldownThreadLimit', () => {
+  it('caps both pools on large hosts', () => {
+    expect(withRolldownThreadLimit({ A: '1' }, 24)).toEqual({
+      A: '1',
+      ROLLDOWN_WORKER_THREADS: '8',
+      RAYON_NUM_THREADS: '8'
+    })
+  })
+
+  it('keeps Rolldown defaults on small hosts and explicit sizes everywhere', () => {
+    expect(withRolldownThreadLimit({}, 8)).toEqual({})
+    expect(withRolldownThreadLimit({ RAYON_NUM_THREADS: '2' }, 24).RAYON_NUM_THREADS).toBe('2')
+  })
+})

config/scripts/run-electron-vite-build.mjs

@@ -3,6 +3,7 @@ import fs from 'node:fs'
 import { createRequire } from 'node:module'
 import path from 'node:path'
 import { appendBuildOldSpaceOption } from './node-old-space-limit.mjs'
+import { withRolldownThreadLimit } from './rolldown-thread-limit.mjs'
 import { RENDERER_BUILD_DIR, verifyRendererBootGraph } from './renderer-boot-graph.mjs'
 
 const require = createRequire(import.meta.url)
@@ -15,7 +16,7 @@ const nodeOptions = appendBuildOldSpaceOption(process.env.NODE_OPTIONS)
 const child = spawn(process.execPath, [electronViteCli, 'build', ...process.argv.slice(2)], {
   stdio: 'inherit',
   env: {
-    ...process.env,
+    ...withRolldownThreadLimit(process.env),
     NODE_OPTIONS: nodeOptions
   }
 })

config/scripts/run-electron-vite-dev.mjs

@@ -7,12 +7,14 @@ import {
   readdirSync,
   readFileSync,
   readlinkSync,
+  renameSync,
   rmSync,
   statSync,
   symlinkSync,
   writeFileSync
 } from 'node:fs'
 import { createRequire } from 'node:module'
+import os from 'node:os'
 import path from 'node:path'
 
 import { prepareDevCliTerminalWrappers } from './dev-cli-terminal-wrapper.mjs'
@@ -36,6 +38,7 @@ import {
   isDevWebClientFresh,
   recordDevWebClientInputs
 } from './dev-web-client-freshness.mjs'
+import { withRolldownThreadLimit } from './rolldown-thread-limit.mjs'
 import { copyPrivateTree } from './space-sharing-copy.mjs'
 import {
   DEV_BUNDLE_ID,
@@ -513,17 +516,53 @@ function prepareDevWebClient() {
     return
   }
   const inputs = captureDevWebClientInputs(repoRoot)
-  console.error('[orca-dev] Building web client for pairing...')
-  execFileSync(
+  console.error('[orca-dev] Building web client for pairing in the background...')
+  // Pairing reads out/web per request, so a stale bundle must not delay Electron startup.
+  // Stage then swap, so an interrupted build never leaves out/web empty.
+  const stagingDir = path.join(repoRoot, 'out', '.web-next')
+  const build = spawn(
     process.execPath,
-    [viteCli, 'build', '--config', path.join(repoRoot, 'vite.web.config.ts')],
-    {
-      cwd: repoRoot,
-      stdio: 'inherit',
-      env: process.env
-    }
+    [
+      viteCli,
+      'build',
+      '--config',
+      path.join(repoRoot, 'vite.web.config.ts'),
+      '--outDir',
+      stagingDir,
+      '--logLevel',
+      'warn'
+    ],
+    { cwd: repoRoot, stdio: 'inherit', env: withRolldownThreadLimit(process.env) }
   )
-  recordDevWebClientInputs(repoRoot, inputs)
+  webClientBuild = build
+  try {
+    os.setPriority(build.pid, os.constants.priority.PRIORITY_BELOW_NORMAL)
+  } catch {
+    // Priority is best effort; the build still runs at normal priority.
+  }
+  build.once('error', (error) => {
+    console.error(`[orca-dev] Web client build failed to start: ${error.message}`)
+  })
+  build.once('exit', (code, signal) => {
+    webClientBuild = null
+    if (code !== 0) {
+      if (!isShuttingDown) {
+        console.error(
+          `[orca-dev] Web client build failed (${signal ?? code}); pairing serves the previous bundle`
+        )
+      }
+      return
+    }
+    try {
+      const outDir = path.dirname(getDevWebClientIndexPath())
+      rmSync(outDir, { recursive: true, force: true })
+      renameSync(stagingDir, outDir)
+      recordDevWebClientInputs(repoRoot, inputs)
+      console.error('[orca-dev] Web client for pairing is ready')
+    } catch (error) {
+      console.error(`[orca-dev] Could not install the web client build: ${error.message}`)
+    }
+  })
 }
 
 if (!isHelpOrVersion && process.env.ORCA_DEV_INSTANCE_LABEL) {
@@ -542,7 +581,6 @@ if (!isHelpOrVersion) {
   forwardedExtras = ports.forwardedExtras
   announceDevInstance({ repoRoot, profile: devProfile, ...ports })
 }
-prepareDevWebClient()
 const forwardedArgs = ['dev', ...forwardedRaw, ...forwardedExtras]
 const child = spawn(process.execPath, [electronViteCli, ...forwardedArgs], {
   stdio: 'inherit',
@@ -551,13 +589,16 @@ const child = spawn(process.execPath, [electronViteCli, ...forwardedArgs], {
   detached: process.platform !== 'win32'
 })
 
+let webClientBuild = null
+let isShuttingDown = false
+
 child.once('spawn', () => {
   if (!isHelpOrVersion) {
     startDevStorageReclaim({ repoRoot })
   }
+  prepareDevWebClient()
 })
 
-let isShuttingDown = false
 let forcedKillTimer = null
 
 function signalExitCode(signal) {
@@ -600,6 +641,7 @@ function beginShutdown(signal) {
   }
   isShuttingDown = true
 
+  webClientBuild?.kill()
   terminateChild(signal)
   forcedKillTimer = setTimeout(() => {
     terminateChild('SIGKILL')
@@ -626,6 +668,8 @@ child.on('exit', (code, signal) => {
   if (forcedKillTimer) {
     clearTimeout(forcedKillTimer)
   }
+  // A half-written out/web must not outlive the session that started it.
+  webClientBuild?.kill()
 
   if (isShuttingDown) {
     process.exit(signalExitCode(signal ?? 'SIGINT'))

config/scripts/run-vite-web-build.mjs

@@ -2,6 +2,7 @@ import { spawn } from 'node:child_process'
 import { createRequire } from 'node:module'
 import path from 'node:path'
 import { appendBuildOldSpaceOption } from './node-old-space-limit.mjs'
+import { withRolldownThreadLimit } from './rolldown-thread-limit.mjs'
 
 const require = createRequire(import.meta.url)
 const vitePackageJson = require.resolve('vite/package.json')
@@ -16,7 +17,7 @@ const child = spawn(
   {
     stdio: 'inherit',
     env: {
-      ...process.env,
+      ...withRolldownThreadLimit(process.env),
       NODE_OPTIONS: nodeOptions
     }
   }

src/main/startup/run-electron-vite-dev-web.test.ts

@@ -230,6 +230,8 @@ describe('run-electron-vite-dev web client prepare', () => {
         }
       })
 
+      // The pairing build runs beside electron-vite instead of before it.
+      await waitFor(() => existsSync(viteFile))
       expect(readFileSync(viteFile, 'utf8')).toContain('build')
 
       const trackedPids = trackPidFile(pidFile)