p-limit 3.1.0

Clean-room public code sample — generation instructions

Write a brand-new, minimal, self-contained code sample in this clean-room directory.
Do not copy, paraphrase, or reference any existing project source. Work only from this spec.

A csx.json manifest scaffold already exists. Do not recreate it from memory. Preserve its case.goal, packages and symbols; fill its empty case.contract with exact assertions and correct its environment, commands and verifierAdapter for the files you generate.

Goal: verify pkg:npm/p-limit@3.1.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:npm/p-limit@3.1.0
Constraints:
  - executionContext: node
Required runtime conditions:
  - ecosystem: npm
  - language: javascript
  - moduleSystem: cjs
  - packageManager: npm@10.9.8
  - runtime: node@22.23.2

Rules:
  - One focused purpose; the smallest project that proves the goal.
  - Include a contract test (test/contract.*) that runs OFFLINE and exits 0 exactly when the goal behavior works.
  - Pin every dependency with a lockfile so resolution is reproducible.
  - No secrets, credentials, or tokens. No real URLs (only example.com or localhost). No absolute paths.
  - No personal names, emails, company names, or project identifiers of any kind.
  - No binaries and no generated output (node_modules, dist, target, venv, .git, .env).
  - Keep it under 200 files and 256KB packed.

{"case":{"caseId":"case:sha256:ce26529a57ef02aeb2cc7ac7c31df35cbc3679f23e2636cbc82878976bf70ac2","constraints":{"executionContext":"node"},"contract":["pLimit restricts concurrent execution of async tasks to the specified concurrency threshold","limit exposes activeCount and pendingCount properties reflecting real-time queue state","limit.clearQueue empties pending queued tasks while allowing active tasks to complete","limit passes through arguments to the wrapped async function and resolves with the return value","pLimit throws a TypeError when initialized with invalid concurrency values"],"goal":"verify pkg:npm/p-limit@3.1.0","kind":"HOW","packages":["pkg:npm/p-limit@3.1.0"],"schemaVersion":1},"contractCommand":["node","test/contract.js"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"npm","executionContext":"node","language":"javascript","libc":"glibc","libcVersion":"2.39","moduleSystem":"cjs","os":"linux","osVersionBucket":"24","packageManager":"npm","packageManagerVersion":"10.9.8","runtime":"node","runtimeVersion":"22.23.2","schemaVersion":1},"license":"MIT-0","packages":["pkg:npm/p-limit@3.1.0"],"schemaVersion":1,"verifierAdapter":"node-typescript@1"}

{
  "name": "p-limit-sample",
  "version": "1.0.0",
  "lockfileVersion": 3,
  "requires": true,
  "packages": {
    "": {
      "name": "p-limit-sample",
      "version": "1.0.0",
      "dependencies": {
        "p-limit": "3.1.0"
      }
    },
    "node_modules/p-limit": {
      "version": "3.1.0",
      "resolved": "https://registry.npmjs.org/p-limit/-/p-limit-3.1.0.tgz",
      "integrity": "sha512-TYOanM3wGwNGsZN2cVTYPArw454xnXj5qmWF1bEoAc4+cU/ol7GVh7odevjp1FNHduHc3KZMcFduxU5Xc6uJRQ==",
      "license": "MIT",
      "dependencies": {
        "yocto-queue": "^0.1.0"
      },
      "engines": {
        "node": ">=10"
      },
      "funding": {
        "url": "https://github.com/sponsors/sindresorhus"
      }
    },
    "node_modules/yocto-queue": {
      "version": "0.1.0",
      "resolved": "https://registry.npmjs.org/yocto-queue/-/yocto-queue-0.1.0.tgz",
      "integrity": "sha512-rVksvsnNCdJ/ohGc6xgPwyN8eheCxsiLM8mxuE/t/mOVqJewPuO1miLpTHQiRgTKCLexL4MeAFVagts7HmNZ2Q==",
      "license": "MIT",
      "engines": {
        "node": ">=10"
      },
      "funding": {
        "url": "https://github.com/sponsors/sindresorhus"
      }
    }
  }
}

{
  "name": "p-limit-sample",
  "version": "1.0.0",
  "dependencies": {
    "p-limit": "3.1.0"
  }
}

{
  "schemaVersion": 1,
  "goal": "verify pkg:npm/p-limit@3.1.0",
  "kind": "HOW",
  "packages": [
    "pkg:npm/p-limit@3.1.0"
  ],
  "constraints": {
    "executionContext": "node"
  },
  "runtimeConditions": {
    "ecosystem": "npm",
    "language": "javascript",
    "moduleSystem": "cjs",
    "packageManager": "npm@10.9.8",
    "runtime": "node@22.23.2"
  }
}

const pLimit = require('p-limit');

/**
 * Creates a concurrency limiter function.
 *
 * @param {number} concurrency - Maximum number of concurrent tasks.
 * @returns {import('p-limit').Limit}
 */
function createLimiter(concurrency) {
  return pLimit(concurrency);
}

/**
 * Executes an async task through a concurrency limiter.
 *
 * @param {import('p-limit').Limit} limiter
 * @param {(...args: any[]) => Promise<any>} fn
 * @param {...any} args
 * @returns {Promise<any>}
 */
function runWithLimit(limiter, fn, ...args) {
  return limiter(fn, ...args);
}

/**
 * Retrieves the current active and pending counts for a limiter.
 *
 * @param {import('p-limit').Limit} limiter
 * @returns {{ activeCount: number, pendingCount: number }}
 */
function getLimiterState(limiter) {
  return {
    activeCount: limiter.activeCount,
    pendingCount: limiter.pendingCount,
  };
}

/**
 * Clears any pending tasks waiting in the limiter queue.
 *
 * @param {import('p-limit').Limit} limiter
 */
function clearLimiterQueue(limiter) {
  limiter.clearQueue();
}

module.exports = {
  createLimiter,
  runWithLimit,
  getLimiterState,
  clearLimiterQueue,
  pLimit,
};

const assert = require('node:assert/strict');
const {
  createLimiter,
  runWithLimit,
  getLimiterState,
  clearLimiterQueue,
} = require('../src/index.js');

const delay = ms => new Promise(resolve => setTimeout(resolve, ms));

async function main() {
  // Contract 1: pLimit restricts concurrent execution of async tasks to the specified concurrency threshold
  {
    const limit = createLimiter(2);
    let active = 0;
    let maxActive = 0;

    const task = async () => {
      active++;
      maxActive = Math.max(maxActive, active);
      await delay(20);
      active--;
      return 'done';
    };

    const results = await Promise.all([
      runWithLimit(limit, task),
      runWithLimit(limit, task),
      runWithLimit(limit, task),
      runWithLimit(limit, task),
      runWithLimit(limit, task),
    ]);

    assert.strictEqual(results.length, 5);
    assert.strictEqual(results.every(r => r === 'done'), true);
    assert.strictEqual(maxActive, 2, 'Max concurrent executions should not exceed concurrency limit');
  }

  // Contract 2: limit exposes activeCount and pendingCount properties reflecting real-time queue state
  {
    const limit = createLimiter(1);
    let release;
    const blocker = new Promise(resolve => {
      release = resolve;
    });

    const p1 = limit(() => blocker);
    const p2 = limit(() => delay(10));
    const p3 = limit(() => delay(10));

    await delay(5);

    const state = getLimiterState(limit);
    assert.strictEqual(state.activeCount, 1, 'activeCount should be 1');
    assert.strictEqual(state.pendingCount, 2, 'pendingCount should be 2');

    release();
    await Promise.all([p1, p2, p3]);

    const finalState = getLimiterState(limit);
    assert.strictEqual(finalState.activeCount, 0, 'activeCount should be 0 after completion');
    assert.strictEqual(finalState.pendingCount, 0, 'pendingCount should be 0 after completion');
  }

  // Contract 3: limit.clearQueue empties pending queued tasks while allowing active tasks to complete
  {
    const limit = createLimiter(1);
    let task1Started = false;
    let task1Finished = false;
    let task2Ran = false;
    let release1;
    const blocker = new Promise(resolve => {
      release1 = resolve;
    });

    const p1 = limit(async () => {
      task1Started = true;
      await blocker;
      task1Finished = true;
      return 'task1';
    });

    const p2 = limit(async () => {
      task2Ran = true;
      return 'task2';
    });

    await delay(5);
    assert.strictEqual(task1Started, true);
    assert.strictEqual(limit.pendingCount, 1);

    clearLimiterQueue(limit);
    assert.strictEqual(limit.pendingCount, 0, 'pendingCount should be 0 after clearQueue');

    release1();
    const res1 = await p1;
    assert.strictEqual(res1, 'task1');
    assert.strictEqual(task1Finished, true);
    assert.strictEqual(task2Ran, false, 'Cleared task should not run');
  }

  // Contract 4: limit passes through arguments to the wrapped async function and resolves with the return value
  {
    const limit = createLimiter(2);
    const multiply = async (a, b) => {
      await delay(5);
      return a * b;
    };

    const res = await runWithLimit(limit, multiply, 6, 7);
    assert.strictEqual(res, 42, 'Limiter should pass arguments and resolve with return value');
  }

  // Contract 5: pLimit throws a TypeError when initialized with invalid concurrency values
  {
    assert.throws(
      () => createLimiter(0),
      {
        name: 'TypeError',
        message: 'Expected `concurrency` to be a number from 1 and up',
      }
    );
    assert.throws(
      () => createLimiter(-1),
      {
        name: 'TypeError',
        message: 'Expected `concurrency` to be a number from 1 and up',
      }
    );
    assert.throws(
      () => createLimiter(1.5),
      {
        name: 'TypeError',
        message: 'Expected `concurrency` to be a number from 1 and up',
      }
    );
    assert.throws(
      () => createLimiter('invalid'),
      {
        name: 'TypeError',
        message: 'Expected `concurrency` to be a number from 1 and up',
      }
    );
  }

  console.log('All pkg:npm/p-limit@3.1.0 contracts passed successfully.');
}

main().catch(err => {
  console.error(err);
  process.exit(1);
});