Promise Pool

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

Installation · Docs · Usage

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Installation

npm i @supercharge/promise-pool

Docs

• 📖 Documentation

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:

1const { PromisePool } = require('@supercharge/promise-pool')
2
3const users = [
4  { name: 'Marcus' },
5  { name: 'Norman' },
6  { name: 'Christian' }
7]
8
9const { results, errors } = await PromisePool
10  .withConcurrency(2)
11  .for(users)
12  .process(async (userData, index, pool) => {
13    const user = await User.createIfNotExisting(userData)
14
15    return user
16  })

The promise pool uses a default concurrency of 10:

1await PromisePool
2  .for(users)
3  .process(async data => {
4    // processes 10 items in parallel by default
5  })

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:

1await PromisePool
2  .for(users)
3  .process(async (user, index, pool) => {
4    if (condition) {
5      return pool.stop()
6    }
7
8    // processes the `user` data
9  })

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

1const { PromisePool } = require('@supercharge/promise-pool')
2
3await PromisePool
4  .for(users)
5  .handleError(async (error, user, pool) => {
6    if (error instanceof SomethingBadHappenedError) {
7      return pool.stop()
8    }
9
10    // handle the given `error`
11  })
12  .process(async (user, index, pool) => {
13    // processes the `user` data
14  })

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.

1const { PromisePool } = require('@supercharge/promise-pool')
2
3try {
4  const errors = []
5
6  const { results } = await PromisePool
7    .for(users)
8    .withConcurrency(4)
9    .handleError(async (error, user) => {
10      if (error instanceof ValidationError) {
11        errors.push(error) // you must collect errors yourself
12        return
13      }
14
15      if (error instanceof ThrottleError) { // Execute error handling on specific errors
16        await retryUser(user)
17        return
18      }
19
20      throw error // Uncaught errors will immediately stop PromisePool
21    })
22    .process(async data => {
23      // the harder you work for something,
24      // the greater you’ll feel when you achieve it
25    })
26
27  await handleCollected(errors) // this may throw
28
29  return { results }
30} catch (error) {
31  await handleThrown(error)
32}

Callback for Started and Finished Tasks

You can use the onTaskStarted and onTaskFinished methods to hook into the processing of tasks. The provided callback for each method will be called when a task started/finished processing:

1const { PromisePool } = require('@supercharge/promise-pool')
2
3await PromisePool
4  .for(users)
5  .onTaskStarted((item, pool) => {
6    console.log(`Progress: ${pool.processedPercentage()}%`)
7    console.log(`Active tasks: ${pool.processedItems().length}`)
8    console.log(`Active tasks: ${pool.activeTasksCount()}`)
9    console.log(`Finished tasks: ${pool.processedItems().length}`)
10    console.log(`Finished tasks: ${pool.processedCount()}`)
11  })
12  .onTaskFinished((item, pool) => {
13    // update a progress bar or something else :)
14  })
15  .process(async (user, index, pool) => {
16    // processes the `user` data
17  })

You can also chain multiple onTaskStarted and onTaskFinished handling (in case you want to separate some functionality):

1const { PromisePool } = require('@supercharge/promise-pool')
2
3await PromisePool
4  .for(users)
5  .onTaskStarted(() => {})
6  .onTaskStarted(() => {})
7  .onTaskFinished(() => {})
8  .onTaskFinished(() => {})
9  .process(async (user, index, pool) => {
10    // processes the `user` data
11  })

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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