emit warning when worker gracefully exit before finish

index.js

@@ -178,6 +178,9 @@ function onWorkerMessage (msg) {
         stream.emit(msg.name, msg.args)
       }
       break
+    case 'WARNING':
+      process.emitWarning(msg.err)
+      break
     default:
       destroy(stream, new Error('this should not happen: ' + msg.code))
   }

lib/worker.js

@@ -151,3 +151,19 @@ process.on('uncaughtException', function (err) {
   })
   process.exit(1)
 })
+
+process.once('exit', exitCode => {
+  if (exitCode !== 0) {
+    process.exit(exitCode)
+    return
+  }
+
+  if (destination?.writableNeedDrain && !destination?.writableEnded) {
+    parentPort.postMessage({
+      code: 'WARNING',
+      err: new Error('ThreadStream: process exited before destination stream was drained. this may indicate that the destination stream try to write to a another missing stream')
+    })
+  }
+
+  process.exit(0)
+})

test/never-drain.test.js

@@ -0,0 +1,40 @@
+const { test } = require('tap')
+const ThreadStream = require('../index')
+const { join } = require('path')
+
+function sleep (ms) {
+  return new Promise((resolve) => {
+    setTimeout(resolve, ms)
+  })
+}
+
+test('emit warning when the worker gracefully exit without the stream ended', async function (t) {
+  const expectedWarning = 'ThreadStream: process exited before destination stream was drained. this may indicate that the destination stream try to write to a another missing stream'
+  const stream = new ThreadStream({
+    filename: join(__dirname, 'to-next.js')
+  })
+
+  let streamWarning
+  function saveWarning (e) {
+    if (e.message === expectedWarning) {
+      streamWarning = e
+    }
+  }
+  process.on('warning', saveWarning)
+
+  for (let i = 0; i < 10_000; i++) {
+    if (streamWarning?.message === expectedWarning) {
+      break
+    }
+    stream.write('hello')
+    await new Promise((resolve) => {
+      setTimeout(resolve, 1)
+    })
+  }
+
+  process.off('warning', saveWarning)
+  await sleep(10)
+
+  t.equal(stream.destroyed, true)
+  t.equal(streamWarning?.message, expectedWarning)
+})

test/to-next.js

@@ -0,0 +1,9 @@
+'use strict'
+
+const { PassThrough } = require('stream')
+
+async function run (opts) {
+  return new PassThrough({})
+}
+
+module.exports = run