feature: allow sync flag to be passed to ThreadStream for synchronous… (#2063)

* feature: allow sync flag to be passed to ThreadStream for synchronous logging

* tests: add unit tests for sync true to ThreadStream

* tests: fix unit test

* tests: fix unit test

Author: karankraina

docs/transports.md

@@ -15,7 +15,7 @@ now referred to as [Legacy Transports](#legacy-transports).
 
 From Pino v7 and upwards transports can also operate inside a [Worker Thread][worker-thread]
 and can be used or configured via the options object passed to `pino` on initialization.
-In this case the transports would always operate asynchronously, and logs would be
+In this case the transports would always operate asynchronously (unless `options.sync` is set to `true` in transport options), and logs would be
 flushed as quickly as possible (there is nothing to do).
 
 [worker-thread]: https://nodejs.org/dist/latest-v14.x/docs/api/worker_threads.html
@@ -124,6 +124,19 @@ const transport = pino.transport({
 pino(transport)
 ```
 
+To make pino log synchronously, pass `sync: true` to transport options.
+```js
+const pino = require('pino')
+const transport = pino.transport({
+  targets: [
+    { target: '/absolute/path/to/my-transport.mjs', level: 'error' },
+  ],
+  dedupe: true,
+  sync: true,
+});
+pino(transport);
+```
+
 For more details on `pino.transport` see the [API docs for `pino.transport`][pino-transport].
 
 [pino-transport]: /docs/api.md#pino-transport

lib/transport.js

@@ -17,11 +17,12 @@ function setupOnExit (stream) {
   })
 }
 
-function buildStream (filename, workerData, workerOpts) {
+function buildStream (filename, workerData, workerOpts, sync) {
   const stream = new ThreadStream({
     filename,
     workerData,
-    workerOpts
+    workerOpts,
+    sync
   })
 
   stream.on('ready', onReady)
@@ -71,7 +72,7 @@ function flush (stream) {
 }
 
 function transport (fullOptions) {
-  const { pipeline, targets, levels, dedupe, worker = {}, caller = getCallers() } = fullOptions
+  const { pipeline, targets, levels, dedupe, worker = {}, caller = getCallers(), sync = false } = fullOptions
 
   const options = {
     ...fullOptions.options
@@ -126,7 +127,7 @@ function transport (fullOptions) {
 
   options.pinoWillSendConfig = true
 
-  return buildStream(fixTarget(target), options, worker)
+  return buildStream(fixTarget(target), options, worker, sync)
 
   function fixTarget (origin) {
     origin = bundlerOverrides[origin] || origin

test/transport/syncTrue.test.js

@@ -0,0 +1,55 @@
+'use strict'
+
+const pino = require('../..')
+const { join } = require('node:path')
+const { readFileSync } = require('node:fs')
+const { test } = require('tap')
+const { file } = require('../helper')
+
+test('thread-stream sync true should log synchronously', async (t) => {
+  const outputPath = file()
+
+  function getOutputLogLines () {
+    return (readFileSync(outputPath)).toString().trim().split('\n').map(JSON.parse)
+  }
+
+  const transport = pino.transport({
+    target: join(__dirname, '..', 'fixtures', 'to-file-transport.js'),
+    options: { destination: outputPath, flush: true },
+    sync: true
+  })
+  const instance = pino(transport)
+
+  var value = { message: 'sync' }
+  instance.info(value)
+  instance.info(value)
+  instance.info(value)
+  instance.info(value)
+  instance.info(value)
+  instance.info(value)
+  let interrupt = false
+  let flushData
+  let loopCounter = 0
+
+  // Start a synchronous loop
+  while (!interrupt && loopCounter < (process.env.MAX_TEST_LOOP_ITERATION || 20000)) {
+    try {
+      loopCounter++
+      const data = getOutputLogLines()
+      flushData = data
+      if (data) {
+        interrupt = true
+        break
+      }
+    } catch (error) {
+      // File may not exist yet
+      // Wait till MAX_TEST_LOOP_ITERATION iterations
+    }
+  }
+
+  if (!interrupt) {
+    throw new Error('Sync loop did not get interrupt')
+  }
+
+  t.equal(flushData.length, 6)
+})