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(() => {
@@ -49,13 +57,12 @@ 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 = await withTimeout<number[]>(
-    const puzzle: number[] = await withTimeout(
     proxy.generate(regionWidth, regionHeight, clues),
     TIMEOUT,
     () => {
@@ -65,7 +72,7 @@ export async function generate(
     }
   );
 
-    available.unshift(proxy);
+  available.push(proxy);
   prettyPrint(regionWidth, regionHeight, puzzle);
   return {
     regionWidth,
@@ -73,7 +80,4 @@ export async function generate(
     size: (regionWidth * regionHeight) ** 2,
     cells: puzzle,
   };
-  } catch (err) {
-    throw err;
-  }
 }