--parallel=auto option

Author: sgravrock

lib/command.js

@@ -1,5 +1,6 @@
 const path = require('path');
 const fs = require('fs');
+const os = require('os');
 const unWindows = require('./unWindows');
 
 exports = module.exports = Command;
@@ -114,9 +115,15 @@ function parseOptions(argv, isWindows) {
     } else if (arg.match("^--reporter=")) {
       reporter = arg.match("^--reporter=(.*)")[1];
     } else if (arg.match("^--parallel=(.*)")) {
-      numWorkers = parseFloat(arg.match("^--parallel=(.*)")[1]);
-      if (isNaN(numWorkers) || numWorkers < 2 || numWorkers !== Math.floor(numWorkers)) {
-        usageErrors.push('Argument to --parallel= must be an integer greater than 1');
+      const w = arg.match("^--parallel=(.*)")[1];
+      if (w === 'auto') {
+        // A reasonable default in most situations
+        numWorkers = os.cpus().length -1;
+      } else {
+        numWorkers = parseFloat(w);
+        if (isNaN(numWorkers) || numWorkers < 2 || numWorkers !== Math.floor(numWorkers)) {
+          usageErrors.push('Argument to --parallel= must be an integer greater than 1');
+        }
       }
     } else if (arg === '--') {
       break;
@@ -291,6 +298,7 @@ function help(options) {
 
   print('Options:');
   print('%s\tRun in parallel with N workers', lPad('--parallel=N', 18));
+  print('%s\tRun in parallel with an automatically chosen number of workers', lPad('--parallel=auto', 18));
   print('%s\tturn off color in spec output', lPad('--no-color', 18));
   print('%s\tforce turn on color in spec output', lPad('--color', 18));
   print('%s\tfilter specs to run only those that match the given string', lPad('--filter=', 18));

spec/command_spec.js

@@ -1,5 +1,6 @@
 const fs = require('fs');
 const path = require('path');
+const os = require('os');
 const Command = require('../lib/command');
 const Loader = require("../lib/loader");
 
@@ -398,6 +399,16 @@ describe('command', function() {
       expect(this.parallelRunner.execute).toHaveBeenCalled();
     });
 
+    it('sets the number of workers to 1 less than CPUs if --paralell is auto', async function() {
+      await this.command.run(['node', 'bin/jasmine.js', '--parallel=auto']);
+      expect(this.fakeJasmine.execute).not.toHaveBeenCalled();
+      expect(this.ParallelRunner).toHaveBeenCalledWith({
+        projectBaseDir,
+        numWorkers: os.cpus().length - 1
+      });
+      expect(this.parallelRunner.execute).toHaveBeenCalled();
+    });
+
     it('shows usage if --parallel is not a number', async function() {
       this.command.run(['node', 'bin/jasmine.js', '--parallel=twelve']);
       expect(this.out.getOutput()).toContain(