Implement WorkerPool, use webkitdirectory input

WorkerPool speeds up processing of plugins by using more cores on separate threads. It terminates and recreates a worker after it finishes a task since web assembly seems to slow down a ton when a worker is reused (maybe memory becomes to large / unfragmented, idk).

I switched to the deprecated input tag with webkitdirectory since it is the only way to load a folder under the program files folder. Drag and drop might be another alternative, but I'd rather have a picker.

components/DataDirPicker.tsx

@@ -1,14 +1,8 @@
-import React, { useContext, useEffect, useRef } from "react";
+import React, { useContext } from "react";
 
-import { WorkersContext } from "../pages/index";
-import { useAppSelector, useAppDispatch } from "../lib/hooks";
-import {
-  addPluginInOrder,
-  clearPlugins,
-  setPending,
-  decrementPending,
-  PluginFile,
-} from "../slices/plugins";
+import { WorkerPoolContext } from "../pages/index";
+import { useAppDispatch } from "../lib/hooks";
+import { clearPlugins, setPending } from "../slices/plugins";
 import styles from "../styles/DataDirPicker.module.css";
 
 export const excludedPlugins = [
@@ -22,49 +16,39 @@ export const excludedPlugins = [
 type Props = {};
 
 const DataDirPicker: React.FC<Props> = () => {
-  const workers = useContext(WorkersContext);
+  const workerPool = useContext(WorkerPoolContext);
   const dispatch = useAppDispatch();
-  const plugins = useAppSelector((state) => state.plugins.plugins);
 
-  const onDataDirButtonClick = async () => {
-    if (workers.length === 0) {
-      return alert("Worker not loaded yet");
+  const onDataDirButtonClick = async (event: {
+    target: { files: FileList | null };
+  }) => {
+    if (!workerPool) {
+      return alert("Workers not loaded yet");
     }
-    const dirHandle = await (
-      window as Window & typeof globalThis & { showDirectoryPicker: () => any }
-    ).showDirectoryPicker();
+    const files = event.target.files ?? [];
     dispatch(clearPlugins());
-    const values = dirHandle.values();
     const plugins = [];
-    while (true) {
-      const next = await values.next();
-      if (next.done) {
-        break;
-      }
+    for (let i = 0; i < files.length; i++) {
+      const file = files[i];
       if (
-        next.value.kind == "file" &&
-        (next.value.name.endsWith(".esp") ||
-          next.value.name.endsWith(".esm") ||
-          next.value.name.endsWith(".esl"))
+        file.name.endsWith(".esp") ||
+        file.name.endsWith(".esm") ||
+        file.name.endsWith(".esl")
       ) {
-        plugins.push(next.value);
+        plugins.push(file);
       }
     }
     dispatch(setPending(plugins.length));
 
     plugins.forEach(async (plugin, index) => {
-      const file = await plugin.getFile();
-      const contents = new Uint8Array(await file.arrayBuffer());
+      const contents = new Uint8Array(await plugin.arrayBuffer());
       try {
-        workers[index % workers.length].postMessage(
-          {
-            skipParsing: excludedPlugins.includes(plugin.name),
-            filename: plugin.name,
-            lastModified: file.lastModified,
-            contents,
-          },
-          [contents.buffer]
-        );
+        workerPool.pushTask({
+          skipParsing: excludedPlugins.includes(plugin.name),
+          filename: plugin.name,
+          lastModified: plugin.lastModified,
+          contents,
+        });
       } catch (error) {
         console.error(error);
       }
@@ -77,9 +61,12 @@ const DataDirPicker: React.FC<Props> = () => {
         To see all of the cell edits and conflicts for your current mod load
         order select your <code>Data</code> directory below to load the plugins.
       </p>
-      <button onClick={onDataDirButtonClick} disabled={workers.length === 0}>
-        {plugins.length === 0 ? "Open" : "Reload"} Skyrim Data directory
-      </button>
+      <input
+        type="file"
+        webkitdirectory=""
+        onChange={onDataDirButtonClick}
+        disabled={!workerPool}
+      />
     </>
   );
 };

lib/WorkerPool.ts

@@ -0,0 +1,81 @@
+import {
+  addPluginInOrder,
+  decrementPending,
+  PluginFile,
+} from "../slices/plugins";
+import store from "./store";
+import { default as Worker } from "worker-loader?filename=static/[fullhash].worker.js!../workers/PluginsLoader.worker";
+
+export interface Task {
+  skipParsing: boolean,
+  filename: string,
+  lastModified: number,
+  contents: Uint8Array,
+}
+
+export class WorkerPool {
+  public taskQueue: Task[];
+  public availableWorkers: Worker[];
+
+  public constructor() {
+    this.taskQueue = [];
+    this.availableWorkers = [];
+  }
+
+  public async init(count: number = 8): Promise<WorkerPool> {
+    this.availableWorkers = [];
+    for (let i = 0; i < count; i++) {
+      this.availableWorkers.push(await this.createWorker());
+    }
+    return this;
+  }
+
+  public async addWorker() {
+    const worker = await this.createWorker();
+    this.availableWorkers.push(worker);
+    this.assignWorker();
+  }
+
+  public async createWorker(): Promise<Worker> {
+    return new Promise((resolve) => {
+      const worker = new Worker();
+      worker.onmessage = (evt: {
+        data: string | PluginFile & { timeHashEnd: number };
+      }) => {
+        const { data } = evt;
+        if (typeof data === "string" && data === "ready") {
+          resolve(worker);
+        } else if (typeof data !== "string") {
+          store.dispatch(decrementPending(1));
+          store.dispatch(addPluginInOrder(data));
+          // Since web assembly memory cannot be shrunk, replace worker with a fresh one to avoid slow repeated
+          // invocations on the same worker instance. Repeated invocations are so slow that the delay in creating a
+          // new worker is worth it. In practice, there are usually more workers than tasks, so the delay does not slow
+          // down processing.
+          worker.terminate();
+          this.addWorker();
+        }
+      };
+    });
+  }
+
+  public pushTask(task: Task) {
+    this.taskQueue.push(task);
+    this.assignWorker();
+  }
+
+  public async assignWorker() {
+    if (this.taskQueue.length > 0 && this.availableWorkers.length > 0) {
+      const task = this.taskQueue.shift()!;
+      const worker = this.availableWorkers.shift()!;
+      worker.postMessage(task, [task.contents.buffer]);
+    }
+  }
+
+  public async terminateAll() {
+    for (const worker of this.availableWorkers) {
+      worker.terminate();
+    }
+    this.availableWorkers = [];
+  }
+}

pages/index.tsx

@@ -1,52 +1,38 @@
-import { createContext, useEffect, useRef, useState } from "react";
+import { createContext, useEffect, useCallback, useState } from "react";
 import type { NextPage } from "next";
 import Head from "next/head";
 import "mapbox-gl/dist/mapbox-gl.css";
 
 import Map from "../components/Map";
-import { useAppDispatch, useAppSelector } from "../lib/hooks";
-import {
-  addPluginInOrder,
-  decrementPending,
-  PluginFile,
-} from "../slices/plugins";
+import { useAppDispatch } from "../lib/hooks";
 import { setPluginsTxtAndApplyLoadOrder } from "../slices/pluginsTxt";
+import { WorkerPool } from "../lib/WorkerPool";
 
-export const WorkersContext = createContext<Worker[]>([]);
+export const WorkerPoolContext = createContext<WorkerPool | null>(null);
 
 const Home: NextPage = () => {
-  const [workers, setWorkers] = useState<Worker[]>([]);
-  const pluginsPending = useAppSelector((state) => state.plugins.pending);
+  const [workerPool, setWorkerPool] = useState<WorkerPool | null>(null);
   const dispatch = useAppDispatch();
 
+  const createWorkerPool = useCallback(async () => {
+    setWorkerPool(
+      await new WorkerPool().init(window.navigator.hardwareConcurrency)
+    );
+  }, []);
+
   useEffect(() => {
-    async function loadWorkers(count: number) {
-      const { default: Worker } = await import(
-        "worker-loader?filename=static/[fullhash].worker.js!../workers/PluginsLoader.worker"
-      );
-      const newWorkers = [];
-      for (let i = 0; i < count; i++) {
-        const worker = new Worker();
-        worker.onmessage = (evt: { data: PluginFile }) => {
-          const { data } = evt;
-          dispatch(decrementPending(1));
-          dispatch(addPluginInOrder(data));
-        };
-        newWorkers.push(worker);
-      }
-      setWorkers(newWorkers);
-    }
-    loadWorkers(window.navigator.hardwareConcurrency ?? 8);
     return () => {
-      if (workers) {
-        for (const worker of workers) {
-          worker.terminate();
-        }
+      if (workerPool) {
+        workerPool.terminateAll();
       }
     };
     // eslint-disable-next-line react-hooks/exhaustive-deps
   }, [dispatch]);
 
+  useEffect(() => {
+    createWorkerPool();
+  }, [createWorkerPool]);
+
   return (
     <>
       <Head>
@@ -95,7 +81,7 @@ const Home: NextPage = () => {
         <meta name="twitter:site" content="@tyhallada" />
         <meta name="twitter:creator" content="@tyhallada" />
       </Head>
-      <WorkersContext.Provider value={workers}>
+      <WorkerPoolContext.Provider value={workerPool}>
         <div
           style={{
             margin: 0,
@@ -119,7 +105,7 @@ const Home: NextPage = () => {
         >
           <Map />
         </div>
-      </WorkersContext.Provider>
+      </WorkerPoolContext.Provider>
     </>
   );
 };

tsconfig.json

@@ -15,6 +15,6 @@
     "jsx": "preserve",
     "incremental": true
   },
-  "include": ["next-env.d.ts", "**/*.ts", "**/*.tsx"],
+  "include": ["next-env.d.ts", "webkitdirectory.d.ts", "**/*.ts", "**/*.tsx"],
   "exclude": ["node_modules"]
 }

webkitdirectory.d.ts

@@ -0,0 +1,8 @@
+import { AriaAttributes, DOMAttributes } from "react";
+
+declare module 'react' {
+  interface HTMLAttributes<T> extends AriaAttributes, DOMAttributes<T> {
+    // extends React's HTMLAttributes
+    webkitdirectory?: boolean | string;
+  }
+}

workers/PluginsLoader.worker.ts

@@ -1,6 +1,8 @@
 import { hash_plugin, parse_plugin } from "skyrim-cell-dump-wasm";
 
-self.addEventListener('message', async (event: MessageEvent<{ skipParsing?: boolean; filename: string; lastModified: number; contents: Uint8Array}>) => {
+self.postMessage("ready");
+
+self.addEventListener('message', async (event: MessageEvent<{ skipParsing?: boolean; filename: string; lastModified: number; contents: Uint8Array }>) => {
   const { skipParsing, filename, lastModified, contents } = event.data;
   let parsed = undefined;
   let parseError = undefined;
@@ -17,7 +19,7 @@ self.addEventListener('message', async (event: MessageEvent<{ skipParsing?: bool
       }
     }
     const hash = hash_plugin(contents).toString(36);
-    self.postMessage({ filename, lastModified, parsed, hash, parseError, enabled: parsed && !parseError });
+    self.postMessage({ filename, lastModified, parsed, hash, parseError, enabled: parsed && !parseError, timeHashEnd: Date.now() });
   } catch (error) {
     console.error(error);
     self.postMessage(error);