Incorporate worker thread id in temporary filename

fixtures/thread-id-test-worker.js

@@ -0,0 +1,3 @@
+'use strict'
+
+require('worker_threads').parentPort.postMessage(require('../thread-id'))

index.js

@@ -4,6 +4,7 @@ var util = require('util')
 var MurmurHash3 = require('imurmurhash')
 var iferr = require('iferr')
 var crypto = require('crypto')
+var threadId = require('./thread-id')
 
 function murmurhex () {
   var hash = MurmurHash3('')
@@ -15,7 +16,7 @@ function murmurhex () {
 
 var invocations = 0
 function getTmpname (filename) {
-  return filename + '.' + murmurhex(__filename, process.pid, ++invocations)
+  return filename + '.' + murmurhex(__filename, process.pid, threadId, ++invocations)
 }
 
 var setImmediate = global.setImmediate || setTimeout

test/thread-id.js

@@ -0,0 +1,30 @@
+'use strict'
+
+var test = require('tap').test
+var path = require('path')
+var threadId = require('../thread-id')
+
+var Worker
+try {
+  Worker = require('worker_threads').Worker
+} catch (e) {}
+
+test('the main process has thread -1', function (t) {
+  t.equal(threadId, -1)
+  t.end()
+})
+
+if (Worker != null) {
+  test('workers have positive integer threadIds', function (t) {
+    t.plan(2)
+
+    var w1 = new Worker(path.join(__dirname, '../fixtures/thread-id-test-worker.js'))
+    w1.once('message', function (message) {
+      t.equal(message, 1)
+    })
+    var w2 = new Worker(path.join(__dirname, '../fixtures/thread-id-test-worker.js'))
+    w2.once('message', function (message) {
+      t.equal(message, 2)
+    })
+  })
+}

thread-id.js

@@ -0,0 +1,16 @@
+'use strict'
+
+var threadId
+try {
+  var Worker = require('worker_threads')
+  if (Worker.isMainThread) {
+    threadId = -1
+  } else {
+    threadId = Worker.threadId
+  }
+} catch (e) {
+  // no worker support
+  threadId = -1
+}
+
+module.exports = threadId