fix: calculate number of workers correctly (#49)

README.md

@@ -61,7 +61,8 @@ use: [
     loader: "thread-loader",
     // loaders with equal options will share worker pools
     options: {
-      // the number of spawned workers, defaults to number of cpus
+      // the number of spawned workers, defaults to (number of cpus - 1) or
+      // fallback to 1 when require('os').cpus() is undefined
       workers: 2,
 
       // number of jobs a worker processes in parallel

src/workerPools.js

@@ -3,10 +3,19 @@ import WorkerPool from './WorkerPool';
 
 const workerPools = Object.create(null);
 
+function calculateNumberOfWorkers() {
+  // There are situations when this call will return undefined so
+  // we are fallback here to 1.
+  // More info on: https://github.com/nodejs/node/issues/19022
+  const cpus = os.cpus() || { length: 1 };
+
+  return Math.max(1, cpus.length - 1);
+}
+
 function getPool(options) {
   const workerPoolOptions = {
     name: options.name || '',
-    numberOfWorkers: options.workers || os.cpus().length,
+    numberOfWorkers: options.workers || calculateNumberOfWorkers(),
     workerNodeArgs: options.workerNodeArgs,
     workerParallelJobs: options.workerParallelJobs || 20,
     poolTimeout: options.poolTimeout || 500,