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/graphql/sudoku.ts

@@ -1,5 +1,5 @@
 import { gql } from "../mods.js";
-import { Sudoku, GenerateArguments, SolveArguments } from "../sudoku/index.js";
+import { generate, GenerateArguments } from "../sudoku/index.js";
 
 export const typeDefs = gql`
   """
@@ -22,22 +22,16 @@ export const typeDefs = gql`
   type Query {
     "Generates a new sudoku."
     generate(regionWidth: Int = 3, regionHeight: Int = 3, clues: Int!): Sudoku!
-
-    "Solves the given sudoku."
-    solve(regionWidth: Int = 3, regionHeight: Int = 3, cells: [Int!]!): Sudoku!
   }
 `;
 
-interface SudokuFuncs {
-  solve(args: SolveArguments): Promise<Sudoku> | Sudoku;
-  generate(args: GenerateArguments): Promise<Sudoku> | Sudoku;
-}
-
 export const resolvers = {
   Query: {
-    generate: (obj: any, args: GenerateArguments, ctx: SudokuFuncs) =>
-      ctx.generate(args),
-    solve: (obj: any, args: SolveArguments, ctx: SudokuFuncs) =>
-      ctx.solve(args),
+    generate: (
+      obj: any,
+      { regionWidth, regionHeight, clues }: GenerateArguments
+    ) => {
+      return generate(regionWidth, regionHeight, clues);
+    },
   },
 };

src/main.ts

@@ -1,13 +1,6 @@
 import { Application, bodyParser } from "./mods.js";
 import { applyGraphQL } from "./graphql.js";
 import { typeDefs, resolvers } from "./graphql/index.js";
-import {
-  initializeWorkers,
-  solve,
-  generate,
-  solveSync,
-  generateSync,
-} from "./sudoku/index.js";
 import stoppable from "stoppable";
 
 import cors from "@koa/cors";
@@ -38,25 +31,10 @@ async function main() {
     );
   });
 
-  let sudokuFuncs: any;
-  if (process.env.USE_WORKER_THREADS) {
-    initializeWorkers();
-    sudokuFuncs = {
-      solve,
-      generate,
-    };
-  } else {
-    sudokuFuncs = {
-      solve: solveSync,
-      generate: generateSync,
-    };
-  }
-
   applyGraphQL({
     app,
     typeDefs: typeDefs,
     resolvers: resolvers,
-    context: () => sudokuFuncs,
   });
 
   runtime.server = stoppable(

src/sudoku/dlx.ts

@@ -114,10 +114,10 @@ export class DLX {
 
     let row = c as DNode;
     while ((row = row.down) !== c) {
-      // traverse down the rows this column
+      // traverse DOWN the rows this column contained
       let col = row;
       while ((col = col.right) !== row) {
-        // traverse the columns of this row to the right
+        // traverse the columns of this row (to the RIGHT)
 
         // remove this node from its column, and shrink its column's size
         this.updates++;

src/sudoku/index.ts

@@ -1,9 +1,7 @@
 import { spawn, Thread, Worker } from "threads";
-import type { ModuleThread } from "threads";
-import { SudokuMath } from "./math.js";
-import { prettyPrint } from "./util.js";
 
 import WORKERS from "physical-cpu-count";
+import { prettyPrint } from "./util.js";
 
 const TIMEOUT = 20000;
 
@@ -15,12 +13,6 @@ export type GenerateArguments = {
   clues: number;
 };
 
-export type SolveArguments = {
-  regionWidth: number;
-  regionHeight: number;
-  cells: Cell[];
-};
-
 export type Sudoku = {
   regionWidth: number;
   regionHeight: number;
@@ -28,41 +20,19 @@ export type Sudoku = {
   cells: Cell[];
 };
 
-type SudokuWorker = {
-  generate: (
-    regionWidth: number,
-    regionHeight: number,
-    clues: number
-  ) => Promise<number[]>;
-  solve: (
-    regionWidth: number,
-    regionHeight: number,
-    cells: number[]
-  ) => Promise<[boolean, number[]]>;
-};
-
-const available: ModuleThread<SudokuWorker>[] = [];
-
-function spawnWorker() {
-  spawn<SudokuWorker>(new Worker("./worker")).then((worker) =>
-    available.push(worker)
-  );
+function getWorker() {
+  return spawn(new Worker("./worker"));
 }
 
-export function initializeWorkers() {
+const available: any = [];
+
+function initialize() {
   console.log(`Starting ${WORKERS} worker threads`);
   for (let n = 0; n < WORKERS; n++) {
-    spawnWorker();
+    getWorker().then((worker) => available.push(worker));
   }
 }
-
-function pickWorker() {
-  const proxy = available.pop();
-  if (!proxy) {
-    throw new Error("No workers available right now. Please try again.");
-  }
-  return proxy;
-}
+initialize();
 
 /**
  * Awaits a promise with a timeout.
@@ -82,33 +52,27 @@ function withTimeout<T>(promise: Promise<T>, ms: number, cb: () => any) {
   }).finally(() => clearTimeout(timeout!));
 }
 
-function workerTaskWithTimeout(
-  task: (worker: ModuleThread) => Promise<any>,
-  timeout: number
-) {
-  const worker = pickWorker();
-  let timedOut = false;
-  return withTimeout(task(worker), timeout, () => {
-    timedOut = true;
-    Thread.terminate(worker);
-    spawnWorker();
-    return new Error("Timed out.");
-  }).finally(() => {
-    if (!timedOut) {
-      available.push(worker);
-    }
-  });
+export async function generate(
+  regionWidth: number,
+  regionHeight: number,
+  clues: number
+): Promise<Sudoku> {
+  const proxy = available.pop();
+  if (!proxy) {
+    throw new Error("No workers available right now. Please try again.");
   }
 
-export async function generate({
-  regionWidth,
-  regionHeight,
-  clues,
-}: GenerateArguments): Promise<Sudoku> {
-  const puzzle = await workerTaskWithTimeout(
-    (worker) => worker.generate(regionWidth, regionHeight, clues),
-    TIMEOUT
+  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.push(proxy);
   prettyPrint(regionWidth, regionHeight, puzzle);
   return {
     regionWidth,
@@ -117,67 +81,3 @@ export async function generate({
     cells: puzzle,
   };
 }
-
-export function generateSync({
-  regionWidth,
-  regionHeight,
-  clues,
-}: GenerateArguments): Sudoku {
-  const math = SudokuMath.get(regionWidth, regionHeight);
-  const cells = math.generate(clues, 1, TIMEOUT);
-  prettyPrint(regionWidth, regionHeight, cells);
-  return {
-    regionWidth,
-    regionHeight,
-    size: (regionWidth * regionHeight) ** 2,
-    cells,
-  };
-}
-
-export async function solve({
-  regionWidth,
-  regionHeight,
-  cells,
-}: SolveArguments): Promise<Sudoku> {
-  const size = (regionWidth * regionHeight) ** 2;
-  if (size !== cells.length) {
-    throw new Error(
-      "The given region dimensions do not align with the number of cells."
-    );
-  }
-  const [solved, result] = await workerTaskWithTimeout(
-    (proxy) => proxy.solve(regionWidth, regionHeight, cells),
-    TIMEOUT
-  );
-  if (!solved) {
-    throw new Error("The given puzzle has no solution.");
-  }
-  return {
-    regionWidth,
-    regionHeight,
-    size,
-    cells: result,
-  };
-}
-
-export function solveSync({
-  regionWidth,
-  regionHeight,
-  cells,
-}: SolveArguments): Sudoku {
-  const size = (regionWidth * regionHeight) ** 2;
-  if (size !== cells.length) {
-    throw new Error(
-      "The given region dimensions do not align with the number of cells."
-    );
-  }
-  if (!SudokuMath.get(regionWidth, regionHeight).solve(cells)) {
-    throw new Error("The given puzzle has no solution.");
-  }
-  return {
-    regionWidth,
-    regionHeight,
-    size,
-    cells,
-  };
-}

src/sudoku/math.ts

@@ -141,28 +141,27 @@ export class SudokuMath {
     return [...firstRow, ...Array(this.values2 - this.values).fill(0)];
   }
 
-  generateComplete(): [number[], number] {
+  generateComplete() {
     const result = this._baseBoard();
     const [header] = this.getDLXHeader(result, true);
-    const dlx = new DLX(header, (solution: DNode[]) => {
+
+    const callback = (solution: DNode[]) => {
       solution.forEach((node) => {
         const meta: NodeMeta = node.meta;
         result[meta.index] = meta.value;
       });
-      // stop after the first solution
+      // return the first solution
       return true;
-    });
+    };
+
+    const dlx = new DLX(header, callback);
 
     dlx.search();
-    return [result, dlx.updates];
+    return result;
   }
 
   generate(clues: number, attempts = Infinity, totalTime = Infinity) {
-    if (clues === 0) {
-      return Array(this.values2).fill(0);
-    }
-
-    let [completed, updates] = this.generateComplete();
+    const completed = this.generateComplete();
 
     const [header, dlxRows] = this.getDLXHeader(); // complete header - no candidates removed
 
@@ -177,93 +176,61 @@ export class SudokuMath {
       candidates[meta.index][meta.value - 1] = node;
     });
 
+    // board positions which have been removed
+    const removed = new Set<number>();
+    const masked: DNode[] = [];
+
     const hasOneSolution = () => {
       solutions = 0;
       dlx.search();
-      updates += dlx.updates;
       return solutions === 1;
     };
 
+    const mask = () => {
+      // mask all DLX rows which are nullified by existing values
+      for (let n = 0; n < this.values2; n++) {
+        if (removed.has(n)) {
+          continue;
+        }
+        const nodes = candidates[n];
+        nodes.forEach((node) => {
+          if (node.meta.value !== completed[n]) {
+            masked.push(node);
+            maskRow(node);
+          }
+        });
+      }
+    };
+
+    const unmask = () => {
+      // unmask all DLX rows
+      while (masked.length > 0) {
+        unmaskRow(masked.pop()!);
+      }
+    };
+
     const start = Date.now();
     const elapsed = () => Date.now() - start;
 
-    // masked rows in the order they were masked
-    const masked: DNode[] = [];
-
-    const maskAtIdx = (idx: number) => {
-      const nodes = candidates[idx];
-      nodes.forEach((node) => {
-        if (node.meta.value !== completed[idx]) {
-          masked.push(node);
-          maskRow(node);
-        }
-      });
-    };
-
-    const removed = new Set<number>();
     const removeable = Array.from(this.indexes);
-
-    const maskUpto = (n: number) => {
-      for (let j = 0; j < n; j++) {
-        // process up to what we've handled
-        const idx = removeable[j];
-        if (removed.has(idx)) {
-          // if we've removed this cell, do not mask it
-          continue;
-        }
-        // otherwise, we had given up it; mask it leaving the original value
-        // we won't try this cell again
-        maskAtIdx(idx);
-      }
-
-      for (let j = this.values2 - 1; j >= n; j--) {
-        // for all those we haven't handled, mask leaving the original values
-        // for us to to attempt to unmask one cell at a time
-        maskAtIdx(removeable[j]);
-      }
-    };
-
-    const unmaskAll = () => {
-      let node;
-      while ((node = masked.pop())) {
-        unmaskRow(node);
-      }
-    };
-
-    const unmaskNextCell = () => {
-      for (let j = 0; j < this.values - 1; j++) {
-        unmaskRow(masked.pop()!);
-      }
-    };
-
-    let best = 0;
     const attempt = () => {
-      // attempt to remove cells until 'clues' cells remain
-      attempts--;
-      removed.clear();
+      // attempt remove cells until 'clues' cells remain
       shuffle(removeable);
-      maskUpto(0);
-
-      for (let i = 0; i < this.values2; i++) {
+      for (let n = 0; n < this.values2; n++) {
         if (elapsed() > totalTime || this.values2 - removed.size == clues) {
           break;
         }
-        unmaskNextCell();
+
+        let toRemove = removeable[n];
+        removed.add(toRemove);
+        mask();
 
         if (!hasOneSolution()) {
-          // failed attempt. prepare for next
-          unmaskAll();
-          maskUpto(i + 1);
-          continue;
+          removed.delete(toRemove);
         }
 
-        removed.add(removeable[i]);
+        unmask();
       }
-      if (removed.size > best) {
-        best = removed.size;
-      }
-
-      unmaskAll();
     };
 
     while (
@@ -273,6 +240,8 @@ export class SudokuMath {
     ) {
       // try to reach the clue goal up to `attempts` times or as long as
       // elapsed time is less than `totalTime`
+      attempts--;
+      removed.clear();
       attempt();
     }
 
@@ -282,28 +251,16 @@ export class SudokuMath {
     return completed;
   }
 
-  solve(puzzle: Cell[]) {
-    const [header] = this.getDLXHeader(puzzle);
-    let solved = false;
+  solve(existing: Cell[]): void {
+    const [header] = this.getDLXHeader(existing);
     const callback = (solution: DNode[]) => {
       solution.forEach((node) => {
         const meta: NodeMeta = node.meta;
-        puzzle[meta.index] = meta.value;
+        existing[meta.index] = meta.value;
       });
-      solved = true;
       // return the first solution
       return true;
     };
     new DLX(header, callback).search();
-    return solved;
-  }
-
-  static maths: { [key: string]: SudokuMath } = {};
-  static get(regionWidth: number, regionHeight: number) {
-    const key = `${regionWidth}:${regionHeight}`;
-    return (
-      SudokuMath.maths[key] ??
-      (SudokuMath.maths[key] = new SudokuMath(regionWidth, regionHeight))
-    );
   }
 }

src/sudoku/worker.js

@@ -1,12 +1,16 @@
 import { SudokuMath } from "./math.js";
 import { expose } from "threads/worker";
 
+const maths = {};
+
 expose({
   generate(regionWidth, regionHeight, clues) {
-    return SudokuMath.get(regionWidth, regionHeight).generate(clues);
-  },
-  solve(regionWidth, regionHeight, cells) {
-    const result = SudokuMath.get(regionWidth, regionHeight).solve(cells);
-    return [result, cells];
+    const math =
+      maths[`${regionWidth}:${regionHeight}`] ||
+      (maths[`${regionWidth}:${regionHeight}`] = new SudokuMath(
+        regionWidth,
+        regionHeight
+      ));
+    return math.generate(clues);
   },
 });