Simplified selectColumnSizeHeuristic

threads.js has better support for modules - no need to give a
project-relative path to the worker file, which complicated the build.

Add rudimentary thread pooling w/ execution timeout.

src/sudoku/index.ts

@@ -34,15 +34,7 @@ function initialize() {
 }
 initialize();
 
-/**
- * Awaits a promise with a timeout.
- *
- * @param promise the promise to await
- * @param ms the timeout in milliseconds
- * @param cb a callback to call when the timeout is reached. The promise is
- *           rejected with whatever gets returned here.
- */
-function withTimeout<T>(promise: Promise<T>, ms: number, cb: () => any) {
+function withTimeout<T>(promise: Promise<T>, ms: number, cb: () => Error) {
   let timeout: NodeJS.Timeout;
   return new Promise<T>((resolve, reject) => {
     timeout = setTimeout(() => {
@@ -57,27 +49,31 @@ export async function generate(
   regionHeight: number,
   clues: number
 ): Promise<Sudoku> {
-  const proxy = available.pop();
+  const proxy = available.shift();
   if (!proxy) {
     throw new Error("No workers available right now. Please try again.");
   }
 
-  const puzzle = await withTimeout<number[]>(
-    proxy.generate(regionWidth, regionHeight, clues),
-    TIMEOUT,
-    () => {
-      Thread.terminate(proxy);
-      getWorker().then((worker) => available.push(worker));
-      return new Error("Timed out. Try reducing the number of clues.");
-    }
-  );
+  try {
+    const puzzle: number[] = await withTimeout(
+      proxy.generate(regionWidth, regionHeight, clues),
+      TIMEOUT,
+      () => {
+        Thread.terminate(proxy);
+        getWorker().then((worker) => available.push(worker));
+        return new Error("Timed out. Try reducing the number of clues.");
+      }
+    );
 
-  available.push(proxy);
-  prettyPrint(regionWidth, regionHeight, puzzle);
-  return {
-    regionWidth,
-    regionHeight,
-    size: (regionWidth * regionHeight) ** 2,
-    cells: puzzle,
-  };
+    available.unshift(proxy);
+    prettyPrint(regionWidth, regionHeight, puzzle);
+    return {
+      regionWidth,
+      regionHeight,
+      size: (regionWidth * regionHeight) ** 2,
+      cells: puzzle,
+    };
+  } catch (err) {
+    throw err;
+  }
 }