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# Based on https://raw.githubusercontent.com/github/gitignore/main/Node.gitignore
# Logs
logs
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npm-debug.log_
yarn-debug.log*
yarn-error.log*
lerna-debug.log*
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report.[0-9]_.[0-9]_.[0-9]_.[0-9]_.json
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*.lcov
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.env
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.parcel-cache
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dist
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MIT License
Copyright (c) 2024 Anton Nesterov
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.

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# Offload
Offload cpu-itensive tasks using WebWorkers. Offload creates a limited execution pool and can operate in two modes:
- callback mode (default) - spawns web workers on demand when the function is called, self terminated
- background - runs workers as backround jobs, distributes load among them, must be terminated manually
*Currently uses unstable api's.*
To install:
```bash
bun add githib:nesterow/offload # or pnpm
```
## Usage
Considering following worker:
```typescript
// echo.worker.ts
import { handler } from "@nesterow/offload";
declare var self: Worker;
handler(async (data: string) => {
await new Promise((resolve) => setTimeout(resolve, 1000));
console.log(data);
return true;
});
```
In the callback mode, `print()` will spawn a worker and terminate it after the task is done.
Maximum of 5 workers may be spawned at the same time, the rest will be queued:
```typescript
import { offload } from "@nesterow/offload";
const [print, terminate] = offload<boolean, string>("./echo.worker.ts", 5);
await print("Hello, World!"); // => true
```
In the background mode, offload will spawn 5 workers, `print()` will distribute the tasks among them:
```typescript
import { offload } from "@nesterow/offload";
const [print, terminate] = offload<boolean, string>("./echo.worker.ts", 5, 'bg');
await print("Hello, World!"); // => true
terminate(); // terminate all workers, for example on exit signal
```
## License
MIT

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import { handler } from "../mod.ts";
const isPrime = (n: number) => {
let result = true;
if (n <= 1) {
result = false;
} else {
for (let i = 2; i * i <= n; i++) {
if (n % i === 0) {
result = false;
break;
}
}
}
return result;
};
handler((n: number) => {
let result = 0;
for (let i = 0; i < n; i++) {
if (isPrime(i)) {
result++;
}
}
return result;
});

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import { handler } from "../mod.ts";
declare var self: Worker;
handler(async (data: any) => {
await new Promise((resolve) => setTimeout(resolve, 1000));
return data;
});

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import { test, expect } from "bun:test";
import { offload } from "../offload";
test(
"count-primes.worker.ts",
async () => {
const [calculatePrime, terminate] = offload<number, number>(
"__test__/count-primes.worker.ts",
);
const result = await calculatePrime(1000000);
expect(result).toBeNumber();
},
{ timeout: 30000 },
);
test("throw-error.worker.ts", async () => {
const [throwError, terminate] = offload<unknown, void>(
"__test__/throw-error.worker.ts",
);
try {
const result = await throwError();
} catch (e) {
expect(e).toBeInstanceOf(Error);
}
});
test("limited queue (size of 3)", async () => {
const [echo, terminate] = offload<number, number>(
"__test__/echo-1s.worker.ts",
3,
);
const results: number[] = [];
for (let i = 0; i < 10; i++) {
echo(i).then((e) => results.push(e));
}
await new Promise((resolve) => setTimeout(resolve, 1050));
expect(results.length).toBe(3);
await new Promise((resolve) => setTimeout(resolve, 1050));
expect(results.length).toBe(6);
console.log("limited queue: Order is not guaranteed:", results);
await new Promise((resolve) => setTimeout(resolve, 2000));
expect(results.length).toBe(10);
console.log("limited queue: Order is not guaranteed:", results);
});
test(
"bg daemons (size of 3)",
async () => {
const [echo, terminate] = offload<number, number>(
"__test__/echo-1s.worker.ts",
3,
"bg",
);
const results: number[] = [];
for (let i = 0; i < 10; i++) {
echo(i).then((e) => results.push(e));
}
await new Promise((resolve) => setTimeout(resolve, 1050));
expect(results.length).toBeLessThanOrEqual(4);
await new Promise((resolve) => setTimeout(resolve, 3000));
expect(results.length).toBe(10);
console.log("bg daemons: Order is not guaranteed:", results);
console.log("bg daemons: Always terminate background jobs");
terminate();
},
{ timeout: 7000 },
);

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import { handler } from "../mod.ts";
handler(async () => {
await new Promise((resolve) => setTimeout(resolve, 1000));
throw new Error("This is an error");
});

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{
"name": "@nesterow/offload",
"version": "0.0.1",
"exports": "./mod.ts"
}

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export * from "./offload.error.ts";
export * from "./offload.handler.ts";
export * from "./offload.ts";

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export class OffloadError extends Error {
constructor(message: string, options?: any) {
super(message, options);
this.name = "OffloadError";
}
}

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import type { WorkerResponse, WorkerRequest } from "./offload.interface";
declare var self: Worker;
type HandlerCallback<T, E> = ((data: E) => T) | ((data: E) => Awaited<T>);
export async function handler<T, E>(fn: HandlerCallback<T, E>): Promise<void> {
self.addEventListener("message", async (event) => {
const request = event.data as WorkerRequest<E>;
const result = await fn(request.params);
const response: WorkerResponse<T> = { id: request.id, value: result };
self.postMessage(response);
});
}

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export type WorkerResponse<T> = { id: number; value: T };
export type WorkerRequest<T> = { id: number; params: T };

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import type { WorkerResponse, WorkerRequest } from "./offload.interface";
import { OffloadError } from "./offload.error";
type URLlike = URL | string;
type Callback<T, E> = (data: E) => Promise<T>;
type Terminator = () => void; // 🦾
type Id = number;
type PromiseTable = Map<
Id,
{ resolve: (value: any) => void; reject: (reason: unknown) => void }
>;
type TaskCallback<T, E> = ((data: E) => Promise<T>) & { [workerId]: Worker };
type WorkerTasks = Map<Worker, PromiseTable>;
const workerId = Symbol("workerId");
const workerTasks: WorkerTasks = new Map();
/**
* OffloadMode
* 'cb' - (default) callback mode, spawns a worker on call and terminates it upon completion
* 'bg' - runs a max number of workers of poolSize constantly in background, balances callbacks among them
*/
export type OffloadMode = "cb" | "bg";
/**
* offload - offload a tasks to a worker
*/
export function offload<Return, Param>(
url: URLlike,
poolSize = 1,
mode: OffloadMode = "cb",
): [Callback<Return, Param>, Terminator] {
switch (mode) {
case "bg":
return createPooledCallback(poolSize, () => {
const bg = withMessageInterceptor(new Worker(url.toString()));
const bgcb = createTaskCallback<Return, Param>(bg);
return bgcb;
});
default:
return createBufferedCallback(poolSize, () => {
const worker = withMessageInterceptor(new Worker(url.toString()));
const cb = createTaskCallback<Return, Param>(worker, () => {
worker.terminate();
});
return cb;
});
}
}
function createTaskCallback<T, E>(
worker: Worker,
eof?: () => void,
): TaskCallback<T, E> {
const cb = async function (data: E): Promise<T> {
const id = createTaskId();
worker.addEventListener(
"error",
(event) => {
const error = event.message;
workerTasks.get(worker)?.get(id)?.reject(new OffloadError(error, id));
workerTasks.get(worker)?.delete(id);
},
{ once: true },
);
const workerTask = Promise.withResolvers<T>();
workerTasks.get(worker)?.set(id, workerTask);
const request: WorkerRequest<E> = { id, params: data };
worker.postMessage(request);
try {
const result = await workerTask.promise;
workerTasks.get(worker)?.delete(id);
if (eof) eof();
return result;
} catch (error) {
workerTasks.get(worker)?.delete(id);
if (eof) eof();
throw error;
}
};
cb[workerId] = worker;
return cb;
}
export function createBufferedCallback<T, E>(
bufSize: number,
fun: () => TaskCallback<T, E>,
): [Callback<T, E>, Terminator] {
let free = bufSize;
const waitFree = async () => {
if (free <= 0) {
await new Promise((resolve) => setTimeout(resolve));
return await waitFree();
}
};
const spots: TaskCallback<T, E>[] = [];
const term = () => {
for (const cb of spots) {
if (cb) terminate(cb);
}
};
const call = async (data: E) => {
if (free <= 0) await waitFree();
--free;
const cb = fun();
spots[free] = cb;
const result = await cb(data);
delete spots[free];
free++;
return result;
};
return [call, term];
}
export function createPooledCallback<T, E>(
poolSize: number,
fun: () => TaskCallback<T, E>,
): [Callback<T, E>, Terminator] {
let free = poolSize;
const waitFree = async () => {
if (free <= 0) {
await new Promise((resolve) => setTimeout(resolve));
return await waitFree();
}
};
const spots: TaskCallback<T, E>[] = [];
for (let i = 0; i < poolSize; i++) {
spots[i] = fun();
}
const term = () => {
for (const cb of spots) {
terminate(cb);
}
};
const call = async (data: E) => {
if (free <= 0) await waitFree();
--free;
const cb = spots[0];
const result = await cb(data);
free++;
return result;
};
return [call, term];
}
function useWorker<T, E>(cb: TaskCallback<T, E>): Worker {
return cb[workerId];
}
function terminate<T, E>(cb: TaskCallback<T, E>): void {
const worker = useWorker(cb);
worker.terminate();
}
function createTaskId(): Id {
return Math.floor(Math.random() * Number.MAX_SAFE_INTEGER);
}
function withMessageInterceptor(worker: Worker): Worker {
const promiseTable: PromiseTable = new Map();
workerTasks.set(worker, promiseTable);
worker.addEventListener("message", (event) => {
const { id, value } = event.data as WorkerResponse<unknown>;
promiseTable.get(id)?.resolve(value);
promiseTable.delete(id);
});
return worker;
}

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{
"name": "@nesterow/offload",
"version": "0.0.1",
"description": "Offload heavy tasks to a separate thread using workers",
"module": "offload.ts",
"type": "module",
"devDependencies": {
"@types/bun": "latest"
},
"peerDependencies": {
"typescript": "^5.0.0"
}
}

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{
"compilerOptions": {
// Enable latest features
"lib": ["ESNext", "DOM"],
"target": "ESNext",
"module": "ESNext",
"moduleDetection": "force",
"jsx": "react-jsx",
"allowJs": true,
// Bundler mode
"moduleResolution": "bundler",
"allowImportingTsExtensions": true,
"verbatimModuleSyntax": true,
"noEmit": true,
// Best practices
"strict": true,
"skipLibCheck": true,
"noFallthroughCasesInSwitch": true,
// Some stricter flags (disabled by default)
"noUnusedLocals": false,
"noUnusedParameters": false,
"noPropertyAccessFromIndexSignature": false
}
}