Lint large test repos in parallel (via worker threads) for shorter run times.

test/markdownlint-test-parallel.js

@@ -0,0 +1,44 @@
+// @ts-check
+
+"use strict";
+
+// eslint-disable-next-line n/no-unsupported-features/node-builtins
+const { availableParallelism } = require("node:os");
+const { Worker } = require("node:worker_threads");
+const markdownlintSync = require("../lib/markdownlint").sync;
+
+/**
+ * Lint specified Markdown files (using multiple threads).
+ *
+ * @param {import("../lib/markdownlint").Options} options Configuration options.
+ * @returns {Promise<import("../lib/markdownlint").LintResults>} Results object.
+ */
+function markdownlintParallel(options) {
+  const workerCount = availableParallelism();
+  const files = options.files || [];
+  const chunkSize = Math.ceil(files.length / workerCount);
+  const promises = [];
+  for (let i = 0; i < workerCount; i++) {
+    promises.push(new Promise((resolve, reject) => {
+      const workerData = {
+        ...options,
+        "files": files.slice(i * chunkSize, (i + 1) * chunkSize)
+      }
+      const worker = new Worker(__filename.replace(/parallel\.js$/, "worker.js"), { workerData });
+      worker.on("message", resolve);
+      worker.on("error", reject);
+    }));
+  }
+  return Promise.all(promises).then((workerResults) => {
+    const combinedResults = markdownlintSync(null);
+    for (const workerResult of workerResults) {
+      // eslint-disable-next-line guard-for-in
+      for (const result in workerResult) {
+        combinedResults[result] = workerResult[result];
+      }
+    }
+    return combinedResults;
+  });
+}
+
+module.exports = markdownlintParallel;