Use worker threads for sudoku generation

Moves sudoku generation off of the main thread. Allows for multiple
generation requests (up to the number of physical CPU cores) to be
served in parallel. Uses the "physical-cpu-count" node package to
determine the numer of physical CPUs of the host.

Also introduces a timeout which causes too-difficult (or impossible)
generation requests to fail if they take more than 5 seconds to
complete. In effect soft-capping the complexity of generated puzzles.

package-lock.json

@@ -276,7 +276,14 @@
     "@types/node": {
       "version": "14.14.31",
       "resolved": "https://registry.npmjs.org/@types/node/-/node-14.14.31.tgz",
-      "integrity": "sha512-vFHy/ezP5qI0rFgJ7aQnjDXwAMrG0KqqIH7tQG5PPv3BWBayOPIQNBjVc/P6hhdZfMx51REc6tfDNXHUio893g=="
+      "integrity": "sha512-vFHy/ezP5qI0rFgJ7aQnjDXwAMrG0KqqIH7tQG5PPv3BWBayOPIQNBjVc/P6hhdZfMx51REc6tfDNXHUio893g==",
+      "dev": true
+    },
+    "@types/physical-cpu-count": {
+      "version": "2.0.0",
+      "resolved": "https://registry.npmjs.org/@types/physical-cpu-count/-/physical-cpu-count-2.0.0.tgz",
+      "integrity": "sha512-kSK757BMb0j/7uP8+UR2wQ7GqrF9+Zk99XvAG4K/sL1VCFEqFoKic3xRHUttsGuTR0WMC3BjOTrf6dUIU+2CmQ==",
+      "dev": true
     },
     "@types/qs": {
       "version": "6.9.5",
@@ -304,6 +311,7 @@
       "version": "1.1.0",
       "resolved": "https://registry.npmjs.org/@types/stoppable/-/stoppable-1.1.0.tgz",
       "integrity": "sha512-BRR23Q9CJduH7AM6mk4JRttd8XyFkb4qIPZu4mdLF+VoP+wcjIxIWIKiBbN78NBbEuynrAyMPtzOHnIp2B/JPQ==",
+      "dev": true,
       "requires": {
         "@types/node": "*"
       }
@@ -1336,6 +1344,11 @@
         "tslib": "^2.0.3"
       }
     },
+    "node-worker-threads-pool": {
+      "version": "1.4.3",
+      "resolved": "https://registry.npmjs.org/node-worker-threads-pool/-/node-worker-threads-pool-1.4.3.tgz",
+      "integrity": "sha512-US55ZGzEDQY2oq8Bc33dFVNKGpx4KaCJqThMDomSsUeX8tMdp2eDjQ6OP0yFd1HTEuHuLqxXSTWC4eidEsbXlg=="
+    },
     "nodemon": {
       "version": "2.0.7",
       "resolved": "https://registry.npmjs.org/nodemon/-/nodemon-2.0.7.tgz",
@@ -1450,6 +1463,11 @@
       "resolved": "https://registry.npmjs.org/path-to-regexp/-/path-to-regexp-6.2.0.tgz",
       "integrity": "sha512-f66KywYG6+43afgE/8j/GoiNyygk/bnoCbps++3ErRKsIYkGGupyv07R2Ok5m9i67Iqc+T2g1eAUGUPzWhYTyg=="
     },
+    "physical-cpu-count": {
+      "version": "2.0.0",
+      "resolved": "https://registry.npmjs.org/physical-cpu-count/-/physical-cpu-count-2.0.0.tgz",
+      "integrity": "sha1-GN4vl+S/epVRrXURlCtUlverpmA="
+    },
     "picomatch": {
       "version": "2.2.2",
       "resolved": "https://registry.npmjs.org/picomatch/-/picomatch-2.2.2.tgz",

package.json

@@ -13,6 +13,8 @@
     "koa": "^2.13.1",
     "koa-bodyparser": "^4.3.0",
     "koa-router": "^9.4.0",
+    "node-worker-threads-pool": "^1.4.3",
+    "physical-cpu-count": "^2.0.0",
     "stoppable": "^1.1.0"
   },
   "devDependencies": {
@@ -20,6 +22,7 @@
     "@types/koa-bodyparser": "^4.3.0",
     "@types/koa-router": "^7.4.1",
     "@types/markdown-it": "^10.0.3",
+    "@types/physical-cpu-count": "^2.0.0",
     "@types/stoppable": "^1.1.0",
     "nodemon": "^2.0.7",
     "ts-node": "^8.10.2",

src/graphql/sudoku.ts

@@ -1,5 +1,5 @@
 import { gql } from "../mods";
-import { generate } from "../sudoku/index";
+import { generate, GenerateArguments } from "../sudoku/index";
 
 export const typeDefs = gql`
   type Cell {
@@ -37,12 +37,6 @@ export const typeDefs = gql`
   }
 `;
 
-type GenerateArguments = {
-  regionWidth: number;
-  regionHeight: number;
-  clues: number;
-};
-
 export const resolvers = {
   Query: {
     generate: (

src/sudoku/index.ts

@@ -1,4 +1,8 @@
 import { SudokuMath } from "./math";
+import { StaticPool, isTimeoutError } from "node-worker-threads-pool";
+
+import WORKERS from "physical-cpu-count";
+const TIMEOUT = 5000;
 
 export type Cell = { value: number | null };
 export type CellArray = Cell[];
@@ -7,6 +11,12 @@ export type Column = CellArray;
 export type Region = CellArray;
 export type Puzzle = CellArray;
 
+export type GenerateArguments = {
+  regionWidth: number;
+  regionHeight: number;
+  clues: number;
+};
+
 export type Sudoku = {
   regionWidth: number;
   regionHeight: number;
@@ -17,21 +27,51 @@ export type Sudoku = {
   regions: () => Region[];
 };
 
-export function generate(
+const pool = new StaticPool<GenerateArguments, [any, Puzzle]>({
+  size: WORKERS,
+  task: "./src/sudoku/worker.js",
+});
+
+const _math = new SudokuMath(0, 0);
+let activeWorkers = 0;
+
+export async function generate(
   regionWidth: number,
   regionHeight: number,
   clues: number
-): Sudoku {
+): Promise<Sudoku> {
-  const math = new SudokuMath(regionWidth, regionHeight);
+  if (activeWorkers >= WORKERS) {
-  const puzzle = math.generatePuzzle(clues);
+    throw new Error("No workers available. Please try again in a moment.");
+  }
 
-  return {
+  try {
-    regionWidth,
+    activeWorkers++;
-    regionHeight,
+    const [math, puzzle] = await pool.exec(
-    cells: math.boardCells,
+      {
-    raw: puzzle,
+        regionWidth,
-    rows: () => math.regionsToRows(puzzle, true),
+        regionHeight,
-    columns: () => math.regionsToCols(puzzle, true),
+        clues,
-    regions: () => math.chunkRegions(puzzle),
+      },
-  };
+      TIMEOUT
+    );
+
+    Object.assign(_math, math);
+
+    return {
+      regionWidth,
+      regionHeight,
+      cells: math.boardCells,
+      raw: puzzle,
+      rows: () => _math.regionsToRows(puzzle, true),
+      columns: () => _math.regionsToCols(puzzle, true),
+      regions: () => _math.chunkRegions(puzzle),
+    };
+  } catch (err) {
+    if (isTimeoutError(err)) {
+      throw new Error("Timed out. Try increasing the number of clues.");
+    }
+    throw err;
+  } finally {
+    activeWorkers--;
+  }
 }

src/sudoku/math.ts

@@ -227,7 +227,6 @@ export class SudokuMath {
       }
       if (fails > removeNext.length) {
         fails = 0;
-        console.log("Backstepping..");
         Array(removed.length)
           .fill(null)
           .forEach(() => replace());

src/sudoku/worker.js

@@ -0,0 +1,8 @@
+const { SudokuMath } = require("./math");
+const { parentPort } = require("worker_threads");
+
+parentPort.on("message", ({ regionWidth, regionHeight, clues }) => {
+  const math = new SudokuMath(regionWidth, regionHeight);
+  const puzzle = math.generatePuzzle(clues);
+  parentPort.postMessage([math, puzzle]);
+});