Allow configuring the number of threads

README.md

@@ -39,6 +39,13 @@ When combined with a watching task (such as [grunt-contrib-watch][watch]), even
 
 ## Options
 
+### `threads`
+
+* Type: `String`, `Boolean`, `Number`
+* Default: `auto`, which is the number of threads -1
+
+Use this option to control the number of threads that grunt-htmllint will use when validating a big number of files. This will spawn as many Java processes as the number of threads.
+
 ### `ignore`
 
 * Type: `Array`, `String`, or `RegExp`

lib/getThreads.js

@@ -0,0 +1,34 @@
+'use strict';
+
+const os = require('os');
+
+// eslint-disable-next-line unicorn/explicit-length-check
+const CPUS = os.cpus() && os.cpus().length;
+const THREADS = CPUS > 2 ? CPUS - 1 : 1;
+
+function getThreads(config) {
+  const { threads } = config;
+
+  const defaultCheck = threads === 'auto' ||
+    threads === -1 ||
+    threads === '' ||
+    threads === true ||
+    threads === null ||
+    typeof threads === 'undefined';
+
+  if (defaultCheck) {
+    return THREADS;
+  }
+
+  if (threads === 0 || threads === 1 || threads === false) {
+    return 1;
+  }
+
+  if (threads > 1) {
+    return threads;
+  }
+
+  throw new Error(`Invalid threads option! (${threads})`);
+}
+
+module.exports = getThreads;

lib/htmllint.js

@@ -1,12 +1,12 @@
 'use strict';
 
-const os = require('os');
 const path = require('path');
 const { execFile } = require('child_process');
 const async = require('async');
 const chunkify = require('./chunkify.js');
-const javaDetect = require('./javaDetect.js');
+const getThreads = require('./getThreads.js');
 const javaArgs = require('./javaArgs.js');
+const javaDetect = require('./javaDetect.js');
 const parseErrorMessages = require('./parseErrorMessages.js');
 const processErrorMessages = require('./processErrorMessages.js');
 
@@ -20,10 +20,6 @@ const MAX_CHARS = 5000;
  */
 const MAX_BUFFER = 20_000 * 1024;
 
-// eslint-disable-next-line unicorn/explicit-length-check
-const CPUS = os.cpus() && os.cpus().length;
-const THREADS = CPUS > 2 ? CPUS - 1 : 1;
-
 function htmllint(config, done) {
   if (config.files.length === 0) {
     return done(null, []);
@@ -42,8 +38,9 @@ function htmllint(config, done) {
 
     const files = config.files.map(file => path.normalize(file));
     const chunks = chunkify(files, MAX_CHARS);
+    const threads = getThreads(config);
 
-    async.mapLimit(chunks, THREADS, (chunk, cb) => {
+    async.mapLimit(chunks, threads, (chunk, cb) => {
       const args = javaArgs(java, chunk, config);
 
       execFile('java', args, { maxBuffer: MAX_BUFFER, shell: true }, (error, stdout, stderr) => {

tasks/html.js

@@ -21,7 +21,8 @@ module.exports = grunt => {
       force: false,
       absoluteFilePathsForReporter: false,
       errorlevels: ['info', 'warning', 'error'],
-      noLangDetect: false
+      noLangDetect: false,
+      threads: 'auto'
     });
     const { force } = options;
     let { reporterOutput } = options;

test/threads_test.js

@@ -0,0 +1,67 @@
+'use strict';
+
+const assert = require('assert').strict;
+const os = require('os');
+const getThreads = require('../lib/getThreads.js');
+
+// eslint-disable-next-line unicorn/explicit-length-check
+const CPUS = os.cpus() && os.cpus().length;
+const THREADS = CPUS > 2 ? CPUS - 1 : 1;
+
+describe('getThreads', () => {
+  it('should use the number of available threads -1', done => {
+    const config = {};
+
+    for (const option of ['auto', true, -1, '', null, undefined]) {
+      config.threads = option;
+      const expected = THREADS;
+      const actual = getThreads(config);
+
+      assert.equal(actual, expected, `"thread: ${option}" failed!`);
+    }
+
+    done();
+  });
+
+  it('threads: false', done => {
+    const config = {
+      threads: false
+    };
+    const expected = 1;
+    const actual = getThreads(config);
+
+    assert.equal(actual, expected);
+    done();
+  });
+
+  it('threads: 4', done => {
+    const config = {
+      threads: 4
+    };
+    const expected = 4;
+    const actual = getThreads(config);
+
+    assert.equal(actual, expected);
+    done();
+  });
+
+  it('threads: -2', done => {
+    const config = {
+      threads: -2
+    };
+    const expected = () => getThreads(config);
+
+    assert.throws(expected, /^Error: Invalid threads/);
+    done();
+  });
+
+  it('threads: "foo"', done => {
+    const config = {
+      threads: 'foo'
+    };
+    const expected = () => getThreads(config);
+
+    assert.throws(expected, /^Error: Invalid threads/);
+    done();
+  });
+});