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: `Number`, `Boolean`, `String`
+* 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/htmllint.js

@@ -16,9 +16,22 @@ const MAX_CHARS = 5000;
 // https://nodejs.org/api/child_process.html#child_process_child_process_exec_command_options_callback
 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 getThreads(options) {
+  // eslint-disable-next-line unicorn/explicit-length-check
+  const cpus = os.cpus() && os.cpus().length;
+  const defaultThreads = cpus > 2 ? cpus - 1 : 1;
+  const { threads } = options;
+
+  if (threads === 'auto' || threads === '' || Boolean(threads) === true) {
+    return defaultThreads;
+  }
+
+  if (threads <= 1 || Boolean(threads) === false) {
+    return 1;
+  }
+
+  return threads;
+}
 
 // Replace left/right quotation marks with normal quotation marks
 function normalizeQuotationMarks(string) {
@@ -135,8 +148,9 @@ 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 = function(grunt) {
       force: false,
       absoluteFilePathsForReporter: false,
       errorlevels: ['info', 'warning', 'error'],
-      noLangDetect: false
+      noLangDetect: false,
+      threads: 'auto'
     });
     const { force } = options;
     let { reporterOutput } = options;