Simplify WorkerPool joining (closes #925)

cli/src/worker_pool.js

@@ -24,7 +24,7 @@ function jobPromise(worker, msg) {
 
 export default class WorkerPool {
   constructor(numWorkers, workerFile) {
-    this.closing = false;
+    this.numWorkers = numWorkers;
     this.jobQueue = new TransformStream();
     this.workerQueue = new TransformStream();
 
@@ -42,7 +42,6 @@ export default class WorkerPool {
     while (true) {
       const { value, done } = await reader.read();
       if (done) {
-        this.workerQueue.writable.close();
         await this._terminateAll();
         return;
       }
@@ -50,12 +49,6 @@ export default class WorkerPool {
       const worker = await this._nextWorker();
       jobPromise(worker, msg).then((result) => {
         resolve(result);
-        // If we are in the process of closing, `workerQueue` is
-        // already closed and we can’t requeue the worker.
-        if (this.closing) {
-          worker.terminate();
-          return;
-        }
         const writer = this.workerQueue.writable.getWriter();
         writer.write(worker);
         writer.releaseLock();
@@ -71,18 +64,15 @@ export default class WorkerPool {
   }
 
   async _terminateAll() {
-    while (true) {
+    for (let n = 0; n < this.numWorkers; n++) {
       const worker = await this._nextWorker();
-      if (!worker) {
-        return;
-      }
       worker.terminate();
     }
+    this.workerQueue.writable.close();
   }
 
   async join() {
-    this.closing = true;
-    this.jobQueue.writable.close();
+    this.jobQueue.writable.getWriter().close();
     await this.done;
   }