Enqueue dev server response work when thread pool is all busy.

generator/src/dev-server.js

@@ -17,6 +17,7 @@ const baseMiddleware = require("./basepath-middleware.js");
  * @param {{ port: string; base: string }} options
  */
 async function start(options) {
+  let threadReadyQueue = [];
   let pool = [];
   ensureDirSync(path.join(process.cwd(), ".elm-pages", "http-response-cache"));
   const cpuCount = os.cpus().length;
@@ -65,6 +66,7 @@ async function start(options) {
     for (let index = 0; index < poolSize; index++) {
       pool.push(initWorker(options.base));
     }
+    runPendingWork();
   }
 
   setup();
@@ -115,7 +117,7 @@ async function start(options) {
     if (request.url && request.url.startsWith("/stream")) {
       handleStream(request, response);
     } else {
-      handleNavigationRequest(request, response, next);
+      await handleNavigationRequest(request, response, next);
     }
   }
 
@@ -226,16 +228,20 @@ async function start(options) {
     );
   }
 
+  /**
+   * @param {string} pathname
+   * @param {((value: any) => any) | null | undefined} onOk
+   * @param {((reason: any) => PromiseLike<never>) | null | undefined} onErr
+   */
   function runRenderThread(pathname, onOk, onErr) {
-    const readyThread = pool.find((thread) => thread.ready);
-    if (!readyThread) {
-      readyThread = pool[0];
-    }
-    const cleanUpThread = () => {
+    let cleanUpThread = () => {};
+    return new Promise(async (resolve, reject) => {
+      const readyThread = await waitForThread();
+      console.log(`Rendering ${pathname}`, readyThread.worker.threadId);
+      cleanUpThread = () => {
         cleanUp(readyThread);
       };
-    return new Promise((resolve, reject) => {
-      if (readyThread) {
+
       readyThread.ready = false;
       readyThread.worker.postMessage({
         mode: "dev-server",
@@ -256,9 +262,6 @@ async function start(options) {
       readyThread.worker.on("error", (error) => {
         reject(error.context);
       });
-      } else {
-        console.error("TODO - running out of ready threads not yet handled");
-      }
     })
       .then(onOk)
       .catch(onErr)
@@ -271,6 +274,7 @@ async function start(options) {
     thread.worker.removeAllListeners("message");
     thread.worker.removeAllListeners("error");
     thread.ready = true;
+    runPendingWork();
   }
 
   /**
@@ -283,7 +287,7 @@ async function start(options) {
     const pathname = urlParts.pathname || "";
     try {
       await pendingCliCompile;
-      runRenderThread(
+      await runRenderThread(
         pathname,
         function (renderResult) {
           const is404 = renderResult.is404;
@@ -357,7 +361,27 @@ async function start(options) {
       next();
     }
   }
+
+  /**
+   * @returns {Promise<{ ready:boolean; worker: Worker }>}
+   * */
+  function waitForThread() {
+    return new Promise((resolve, reject) => {
+      threadReadyQueue.push(resolve);
+      runPendingWork();
+    });
   }
+
+  function runPendingWork() {
+    const readyThreads = pool.filter((thread) => thread.ready);
+    readyThreads.forEach((readyThread) => {
+      const startTask = threadReadyQueue.shift();
+      if (startTask) {
+        startTask(readyThread);
+      }
+    });
+  }
+
   /**
    * @param {string} basePath
    */
@@ -374,6 +398,7 @@ function initWorker(basePath) {
     });
     return newWorker;
   }
+}
 
 function timeMiddleware() {
   return (req, res, next) => {