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

@@ -34,7 +34,15 @@ function initialize() {
 }
 initialize();
 
-function withTimeout<T>(promise: Promise<T>, ms: number, cb: () => Error) {
+/**
+ * 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) {
   let timeout: NodeJS.Timeout;
   return new Promise<T>((resolve, reject) => {
     timeout = setTimeout(() => {
@@ -49,31 +57,27 @@ export async function generate(
   regionHeight: number,
   clues: number
 ): Promise<Sudoku> {
-  const proxy = available.shift();
+  const proxy = available.pop();
   if (!proxy) {
     throw new Error("No workers available right now. Please try again.");
   }
 
-  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.");
-      }
-    );
+  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.");
+    }
+  );
 
-    available.unshift(proxy);
-    prettyPrint(regionWidth, regionHeight, puzzle);
-    return {
-      regionWidth,
-      regionHeight,
-      size: (regionWidth * regionHeight) ** 2,
-      cells: puzzle,
-    };
-  } catch (err) {
-    throw err;
-  }
+  available.push(proxy);
+  prettyPrint(regionWidth, regionHeight, puzzle);
+  return {
+    regionWidth,
+    regionHeight,
+    size: (regionWidth * regionHeight) ** 2,
+    cells: puzzle,
+  };
 }