Fix sample collection when using worker threads

injects/sampler.js

@@ -1,22 +1,36 @@
 'use strict'
 
+// Important to keep in mind that every Node.js worker thread
+// will run it's own instance of the sample.js.
+
 const fs = require('fs')
 const makeDir = require('mkdirp')
 const systemInfo = require('../collect/system-info.js')
 const ProcessStat = require('../collect/process-stat.js')
 const getLoggingPaths = require('@nearform/clinic-common').getLoggingPaths('doctor')
 const ProcessStatEncoder = require('../format/process-stat-encoder.js')
+const { isMainThread, threadId } = require('worker_threads')
 
 // create encoding files and directory
 const paths = getLoggingPaths({ path: process.env.NODE_CLINIC_DOCTOR_DATA_PATH, identifier: process.pid })
 
 makeDir.sync(paths['/'])
 
-// write system file
-fs.writeFileSync(paths['/systeminfo'], JSON.stringify(systemInfo(), null, 2))
+// write system file only on the main thread
+if (isMainThread) {
+  fs.writeFileSync(paths['/systeminfo'], JSON.stringify(systemInfo(), null, 2))
+}
 
 const processStatEncoder = new ProcessStatEncoder()
-const out = processStatEncoder.pipe(fs.createWriteStream(paths['/processstat']))
+
+// If sampling in a worker thread, we have to write samples
+// out to a separate processstat file.
+let outpath = paths['/processstat']
+if (!isMainThread) {
+  outpath += `-${threadId}`
+}
+
+const out = processStatEncoder.pipe(fs.createWriteStream(outpath))
 
 // sample every 10ms
 const processStat = new ProcessStat(parseInt(

test/cmd-collect-analysing-worker.test.js

@@ -0,0 +1,37 @@
+'use strict'
+
+const { test } = require('tap')
+const rimraf = require('rimraf')
+const ClinicDoctor = require('../index.js')
+
+test('cmd - test collect - emits "analysing" event', function (t) {
+  const tool = new ClinicDoctor()
+
+  function cleanup (err, dirname) {
+    t.ifError(err)
+    t.match(dirname, /^[0-9]+\.clinic-doctor/)
+    rimraf(dirname, (err) => {
+      t.ifError(err)
+      t.end()
+    })
+  }
+
+  let seenAnalysing = false
+  tool.on('analysing', () => {
+    seenAnalysing = true
+  })
+
+  const expr = 'setTimeout(() => {}, 123);' +
+               'const { Worker } = require("worker_threads");' +
+               'new Worker("setTimeout(() => {}, 123);", { eval: true });'
+
+  tool.collect(
+    [process.execPath, '-e', expr],
+    function (err, dirname) {
+      if (err) return cleanup(err, dirname)
+
+      t.ok(seenAnalysing) // should've happened before this callback
+      cleanup(null, dirname)
+    }
+  )
+})