@supercharge/promise-pool

What is @supercharge/promise-pool?

@supercharge/promise-pool is an npm package that allows you to process a large number of promises concurrently with a specified limit on the number of promises that can run at the same time. This helps in managing resources efficiently and avoiding overwhelming the system.

What are @supercharge/promise-pool's main functionalities?

Concurrent Processing

This feature allows you to process a list of items concurrently with a specified limit on the number of concurrent operations. In this example, the concurrency limit is set to 5.

const { PromisePool } = require('@supercharge/promise-pool');

async function processItems(items) {
  const { results, errors } = await PromisePool
    .for(items)
    .withConcurrency(5)
    .process(async item => {
      // Process each item
      return await processItem(item);
    });

  console.log('Results:', results);
  console.log('Errors:', errors);
}

async function processItem(item) {
  // Simulate async processing
  return new Promise(resolve => setTimeout(() => resolve(item), 1000));
}

processItems([1, 2, 3, 4, 5, 6, 7, 8, 9, 10]);

Error Handling

This feature demonstrates how to handle errors that occur during the processing of items. Errors are collected and can be reviewed after the processing is complete.

const { PromisePool } = require('@supercharge/promise-pool');

async function processItems(items) {
  const { results, errors } = await PromisePool
    .for(items)
    .withConcurrency(5)
    .process(async item => {
      if (item % 2 === 0) {
        throw new Error('Even number error');
      }
      return await processItem(item);
    });

  console.log('Results:', results);
  console.log('Errors:', errors);
}

async function processItem(item) {
  // Simulate async processing
  return new Promise(resolve => setTimeout(() => resolve(item), 1000));
}

processItems([1, 2, 3, 4, 5, 6, 7, 8, 9, 10]);

Dynamic Concurrency

This feature allows you to dynamically set the concurrency level based on certain conditions. In this example, the concurrency is set to 10 if the number of items is greater than 5, otherwise, it is set to 2.

const { PromisePool } = require('@supercharge/promise-pool');

async function processItems(items) {
  const concurrency = items.length > 5 ? 10 : 2;
  const { results, errors } = await PromisePool
    .for(items)
    .withConcurrency(concurrency)
    .process(async item => {
      return await processItem(item);
    });

  console.log('Results:', results);
  console.log('Errors:', errors);
}

async function processItem(item) {
  // Simulate async processing
  return new Promise(resolve => setTimeout(() => resolve(item), 1000));
}

processItems([1, 2, 3, 4, 5, 6, 7, 8, 9, 10]);

Other packages similar to @supercharge/promise-pool

p-limit

p-limit is a package that allows you to run multiple promise-returning & async functions with a concurrency limit. It is simpler and more lightweight compared to @supercharge/promise-pool, but it lacks some of the advanced features like error collection and dynamic concurrency.

async

async is a utility module which provides straight-forward, powerful functions for working with asynchronous JavaScript. It includes a variety of methods for managing concurrency, such as `async.eachLimit` and `async.queue`. It is more feature-rich and versatile compared to @supercharge/promise-pool, but it can be more complex to use.

bluebird

bluebird is a fully featured promise library with focus on innovative features and performance. It includes methods like `Promise.map` which can be used to limit concurrency. It is more comprehensive and offers more features beyond just concurrency control compared to @supercharge/promise-pool.

README

Promise Pool

Map-like, concurrent promise processing for Node.js.

Installation · Docs · Usage

Follow @marcuspoehls and @superchargejs for updates!

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Installation

npm i @supercharge/promise-pool

Docs

Find all the details and available methods in the extensive Supercharge docs.

Usage

Using the promise pool is pretty straightforward. The package exposes a class and you can create a promise pool instance using the fluent interface.

Here’s an example using a concurrency of 2:

const { PromisePool } = require('@supercharge/promise-pool')

const users = [
  { name: 'Marcus' },
  { name: 'Norman' },
  { name: 'Christian' }
]

const { results, errors } = await PromisePool
  .withConcurrency(2)
  .for(users)
  .process(async (userData, index, pool) => {
    const user = await User.createIfNotExisting(userData)

    return user
  })

The promise pool uses a default concurrency of 10:

await PromisePool
  .for(users)
  .process(async data => {
    // processes 10 items in parallel by default
  })

Manually Stop the Pool

You can stop the processing of a promise pool using the pool instance provided to the .process() and .handleError() methods. Here’s an example how you can stop an active promise pool from within the .process() method:

await PromisePool
  .for(users)
  .process(async (user, index, pool) => {
    if (condition) {
      return pool.stop()
    }

    // processes the `user` data
  })

You may also stop the pool from within the .handleError() method in case you need to:

const { PromisePool } = require('@supercharge/promise-pool')

await PromisePool
  .for(users)
  .handleError(async (error, user, pool) => {
    if (error instanceof SomethingBadHappenedError) {
      return pool.stop()
    }

    // handle the given `error`
  })
  .process(async (user, index, pool) => {
    // processes the `user` data
  })

Bring Your Own Error Handling

The promise pool allows for custom error handling. You can take over the error handling by implementing an error handler using the .handleError(handler).

If you provide an error handler, the promise pool doesn’t collect any errors. You must then collect errors yourself.

Providing a custom error handler allows you to exit the promise pool early by throwing inside the error handler function. Throwing errors is in line with Node.js error handling using async/await.

const { PromisePool } = require('@supercharge/promise-pool')

try {
  const errors = []

  const { results } = await PromisePool
    .for(users)
    .withConcurrency(4)
    .handleError(async (error, user) => {
      if (error instanceof ValidationError) {
        errors.push(error) // you must collect errors yourself
        return
      }

      if (error instanceof ThrottleError) { // Execute error handling on specific errors
        await retryUser(user)
        return
      }

      throw error // Uncaught errors will immediately stop PromisePool
    })
    .process(async data => {
      // the harder you work for something,
      // the greater you’ll feel when you achieve it
    })

  await handleCollected(errors) // this may throw

  return { results }
} catch (error) {
  await handleThrown(error)
}

Contributing

1. Create a fork
2. Create your feature branch: git checkout -b my-feature
3. Commit your changes: git commit -am 'Add some feature'
4. Push to the branch: git push origin my-new-feature
5. Submit a pull request 🚀

License

MIT © Supercharge

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superchargejs.com  ·  GitHub @supercharge  ·  Twitter @superchargejs

Changelog

2.1.0 - 2021-12-14

Added

• keep the original error in error.raw
  • this is useful if your errors store some kind of context
  • the PromisePoolError instance would otherwise loose the original error context

class CustomError extends Error { … }

const { errors } = await PromisePool
  .withConcurrency(2)
  .for([1, 2, 3])
  .process(() => {
    throw new CustomError('Oh no')
  })

errors[0].raw instanceof CustomError
// true

Updated

• bump dependencies
• run tests for Node.js v17