perf(dev): warm a single fork by default, overridable with NUXT_DEV_FORK_POOL_SIZE

Author: danielroe

packages/nuxt-cli/src/commands/dev.ts

@@ -171,7 +171,7 @@ const command = defineCommand({
 
     const pool = new ForkPool({
       rawArgs: ctx.rawArgs,
-      poolSize: 2,
+      poolSize: resolveForkPoolSize(),
       listenOverrides,
       inspect,
     })
@@ -276,6 +276,19 @@ function setupSignalHandlers(close: () => Promise<void>): void {
   }
 }
 
+function resolveForkPoolSize(): number | undefined {
+  const raw = process.env.NUXT_DEV_FORK_POOL_SIZE
+  if (!raw) {
+    return undefined
+  }
+  const parsed = Number(raw)
+  if (!Number.isInteger(parsed) || parsed < 0) {
+    logger.warn(`Ignoring invalid \`NUXT_DEV_FORK_POOL_SIZE=${raw}\`; expected a non-negative integer.`)
+    return undefined
+  }
+  return parsed
+}
+
 function parsePositiveInteger(value: string | undefined): number | undefined {
   const parsed = Number(value)
   if (!value || !Number.isInteger(parsed) || parsed <= 0) {

packages/nuxt-cli/src/dev/pool.ts

@@ -30,7 +30,7 @@ export class ForkPool {
 
   constructor(options: ForkPoolOptions) {
     this.rawArgs = options.rawArgs
-    this.poolSize = options.poolSize ?? 2
+    this.poolSize = options.poolSize ?? 1
     this.listenOverrides = options.listenOverrides
     this.inspect = options.inspect
 

packages/nuxt-cli/test/unit/fork-pool.spec.ts

@@ -28,6 +28,13 @@ afterEach(async () => {
 })
 
 describe('forkPool', () => {
+  it('should warm a single fork by default', { timeout: 30_000 }, async () => {
+    const pool = createPool()
+    pool.startWarming()
+    await waitForReady(pool, 1)
+    expect(pool.getStats().total).toBe(1)
+  })
+
   it('should kill every fork on shutdown', { timeout: 30_000 }, async () => {
     const pool = createPool(3)
     pool.startWarming()