fix!: change default pool to 'forks' (#5047)

docs/config/index.md

@@ -586,7 +586,7 @@ By providing an object instead of a string you can define individual outputs whe
 ### pool<NonProjectOption /> <Badge type="info">1.0.0+</Badge> {#pool}
 
 - **Type:** `'threads' | 'forks' | 'vmThreads' | 'vmForks'`
-- **Default:** `'threads'`
+- **Default:** `'forks'` (in v1 `'threads'`)
 - **CLI:** `--pool=threads`
 
 Pool used to run tests in.

docs/guide/common-errors.md

@@ -65,9 +65,8 @@ This error can happen when NodeJS's `fetch` is used with default [`pool: 'thread
 
 As work-around you can switch to [`pool: 'forks'`](/config/#forks) or [`pool: 'vmForks'`](/config/#vmforks).
 
-Specify `pool` in your configuration file:
-
-```ts
+::: code-group
+```ts [vitest.config.js]
 import { defineConfig } from 'vitest/config'
 
 export default defineConfig({
@@ -76,12 +75,33 @@ export default defineConfig({
   },
 })
 ```
+```bash [CLI]
+vitest --pool=forks
+```
+:::
 
-Or in your `package.json` scripts:
+## Segfaults and native code errors
 
-```diff
-scripts: {
--  "test": "vitest"
-+  "test": "vitest --pool=forks"
-}
+Running [native NodeJS modules](https://nodejs.org/api/addons.html) in `pool: 'threads'` can run into cryptic errors coming from the native code.
+
+- `Segmentation fault (core dumped)`
+- `thread '<unnamed>' panicked at 'assertion failed`
+- `Abort trap: 6`
+- `internal error: entered unreachable code`
+
+In these cases the native module is likely not built to be multi-thread safe. As work-around, you can switch to `pool: 'forks'` which runs the test cases in multiple `node:child_process` instead of multiple `node:worker_threads`.
+
+::: code-group
+```ts [vitest.config.js]
+import { defineConfig } from 'vitest/config'
+
+export default defineConfig({
+  test: {
+    pool: 'forks',
+  },
+})
+```
+```bash [CLI]
+vitest --pool=forks
 ```
+:::

docs/guide/improving-performance.md

@@ -1,5 +1,7 @@
 # Improving Performance
 
+## Test isolation
+
 By default Vitest runs every test file in an isolated environment based on the [pool](/config/#pool):
 
 - `threads` pool runs every test file in a separate [`Worker`](https://nodejs.org/api/worker_threads.html#class-worker)
@@ -49,3 +51,24 @@ export default defineConfig({
 })
 ```
 :::
+
+## Pool
+
+By default Vitest runs tests in `pool: 'forks'`. While `'forks'` pool is better for compatibility issues ([hanging process](/guide/common-errors.html#failed-to-terminate-worker) and [segfaults](/guide/common-errors.html#segfaults-and-native-code-errors)), it may be slightly slower than `pool: 'threads'` in larger projects.
+
+You can try to improve test run time by switching `pool` option in configuration:
+
+::: code-group
+```bash [CLI]
+vitest --pool=threads
+```
+```ts [vitest.config.js]
+import { defineConfig } from 'vitest/config'
+
+export default defineConfig({
+  test: {
+    pool: 'threads',
+  },
+})
+```
+:::

packages/vitest/src/defaults.ts

@@ -67,7 +67,7 @@ const config = {
   watch: !isCI,
   globals: false,
   environment: 'node' as const,
-  pool: 'threads' as const,
+  pool: 'forks' as const,
   clearMocks: false,
   restoreMocks: false,
   mockReset: false,

test/browser/vitest.config.unit.mts

@@ -4,8 +4,8 @@ export default defineConfig({
   test: {
     include: ['specs/**/*.{spec,test}.ts'],
     poolOptions: {
-      threads: {
-        singleThread: true,
+      forks: {
+        singleFork: true,
       },
     },
     hookTimeout: process.env.CI ? 120_000 : 10_000,

test/config/test/chai-config.test.ts

@@ -18,8 +18,7 @@ describe('truncateThreshold', () => {
       ok 6 - test-each-title.test.ts > [ 'one', 'two', 'three', 'four', …(1) ]
       ok 7 - test-each-title.test.ts > { one: 1, two: 2, three: 3 }
       ok 8 - test-each-title.test.ts > { one: 1, two: 2, three: 3, four: 4 }
-      ok 9 - test-each-title.test.ts > { one: 1, two: 2, three: 3, …(2) }
-      "
+      ok 9 - test-each-title.test.ts > { one: 1, two: 2, three: 3, …(2) }"
     `)
     expect(result.exitCode).toBe(0)
   })
@@ -43,8 +42,7 @@ describe('truncateThreshold', () => {
       ok 6 - test-each-title.test.ts > [ 'one', 'two', 'three', 'four', …(1) ]
       ok 7 - test-each-title.test.ts > { one: 1, two: 2, three: 3 }
       ok 8 - test-each-title.test.ts > { one: 1, two: 2, three: 3, four: 4 }
-      ok 9 - test-each-title.test.ts > { one: 1, two: 2, three: 3, …(2) }
-      "
+      ok 9 - test-each-title.test.ts > { one: 1, two: 2, three: 3, …(2) }"
     `)
     expect(result.exitCode).toBe(0)
   })
@@ -68,14 +66,13 @@ describe('truncateThreshold', () => {
       ok 6 - test-each-title.test.ts > [ 'one', 'two', 'three', 'four', 'five' ]
       ok 7 - test-each-title.test.ts > { one: 1, two: 2, three: 3 }
       ok 8 - test-each-title.test.ts > { one: 1, two: 2, three: 3, four: 4 }
-      ok 9 - test-each-title.test.ts > { one: 1, two: 2, three: 3, four: 4, five: 5 }
-      "
+      ok 9 - test-each-title.test.ts > { one: 1, two: 2, three: 3, four: 4, five: 5 }"
     `)
     expect(result.exitCode).toBe(0)
   })
 })
 
 function cleanOutput(output: string) {
   // remove non-deterministic output
-  return output.replaceAll(/\s*# time=.*/g, '')
+  return output.replaceAll(/\s*# time=.*/g, '').trim()
 }

test/config/test/failures.test.ts

@@ -144,7 +144,6 @@ test('boolean flag 100 should not crash CLI', async () => {
 
 test('nextTick cannot be mocked inside child_process', async () => {
   const { stderr } = await runVitest({
-    pool: 'forks',
     fakeTimers: { toFake: ['nextTick'] },
     include: ['./fake-timers.test.ts'],
   })
@@ -154,6 +153,7 @@ test('nextTick cannot be mocked inside child_process', async () => {
 
 test('nextTick can be mocked inside worker_threads', async () => {
   const { stderr } = await runVitest({
+    pool: 'threads',
     fakeTimers: { toFake: ['nextTick'] },
     include: ['./fixtures/test/fake-timers.test.ts'],
   })

test/watch/vitest.config.ts

@@ -13,13 +13,10 @@ export default defineConfig({
     testTimeout: process.env.CI ? 60_000 : 10_000,
 
     // Test cases may have side effects, e.g. files under fixtures/ are modified on the fly to trigger file watchers
-    poolOptions: {
-      forks: { singleFork: true },
-      threads: { singleThread: true },
-      vmThreads: { singleThread: true },
-    },
+    fileParallelism: false,
 
     // TODO: Fix flakiness and remove
     allowOnly: true,
+    bail: 1,
   },
 })