feat: support configure maxTheads and minThreads (#59)

Co-authored-by: Anthony Fu <anthonyfu117@hotmail.com>

README.md

@@ -81,7 +81,7 @@ $ npx vitest
 - Create `vitest.config.ts`, which will have the higher priority
 - Pass `--config` option to CLI, e.g. `vitest --config ./path/to/vitest.config.ts`
 - Use `process.env.VITEST` to conditionally apply differnet configuration in `vite.config.ts`
-
+- Use `process.env.VITEST_MAX_THREADS` to limit amount of worker threads
 To configure `vitest` itself, add `test` property in your Vite config
 
 ```ts

src/node/init.ts

@@ -54,10 +54,8 @@ export async function initViteServer(options: CliOptions = {}) {
 
   resolved.interpretDefault = resolved.interpretDefault || true
 
-  const env = process.env
-  const CI = !!env.CI
-  const UPDATE_SNAPSHOT = resolved.update || env.UPDATE_SNAPSHOT
-
+  const CI = !!process.env.CI
+  const UPDATE_SNAPSHOT = resolved.update || process.env.UPDATE_SNAPSHOT
   resolved.snapshotOptions = {
     updateSnapshot: CI && !UPDATE_SNAPSHOT
       ? 'none'
@@ -66,6 +64,12 @@ export async function initViteServer(options: CliOptions = {}) {
         : 'new',
   } as SnapshotStateOptions
 
+  if (process.env.VITEST_MAX_THREADS)
+    resolved.maxThreads = parseInt(process.env.VITEST_MAX_THREADS)
+
+  if (process.env.VITEST_MIN_THREADS)
+    resolved.minThreads = parseInt(process.env.VITEST_MIN_THREADS)
+
   return {
     server,
     config: resolved,

src/node/pool.ts

@@ -15,6 +15,8 @@ export interface WorkerPool {
 export function createWorkerPool(ctx: VitestContext) {
   const piscina = new Piscina({
     filename: new URL('./dist/node/worker.js', pathToFileURL(distDir)).href,
+    maxThreads: ctx.config.maxThreads,
+    minThreads: ctx.config.minThreads,
   })
 
   const runTestFiles: WorkerPool['runTestFiles'] = async(files, invalidates) => {

src/types.ts

@@ -81,6 +81,27 @@ export interface UserOptions {
   reporter?: Reporter
 
   /**
+   * Enable multi-threading
+   *
+   * @default true
+   */
+  threads?: boolean
+
+  /**
+   * Maximum number of threads
+   *
+   * @default available CPUs
+   */
+  maxThreads?: number
+
+  /**
+   * Minimum number of threads
+   *
+   * @default available CPUs
+   */
+  minThreads?: number
+
+  /*
    * Interpret CJS module's default as named exports
    *
    * @default true