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@supercharge/promise-pool
Advanced tools
Changelog
3.1.0 - 2023-09-25
pool.handleError
after pool.for
: previously the error handler was lostReadme
Map-like, concurrent promise processing for Node.js.
Installation · Docs · Usage
Follow @marcuspoehls and @superchargejs for updates!
npm i @supercharge/promise-pool
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:
import { PromisePool } from '@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
})
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:
import { PromisePool } from '@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
})
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.
import { PromisePool } from '@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)
}
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:
import { PromisePool } from '@supercharge/promise-pool'
await PromisePool
.for(users)
.onTaskStarted((item, pool) => {
console.log(`Progress: ${pool.processedPercentage()}%`)
console.log(`Active tasks: ${pool.processedItems().length}`)
console.log(`Active tasks: ${pool.activeTasksCount()}`)
console.log(`Finished tasks: ${pool.processedItems().length}`)
console.log(`Finished tasks: ${pool.processedCount()}`)
})
.onTaskFinished((item, pool) => {
// update a progress bar or something else :)
})
.process(async (user, index, pool) => {
// processes the `user` data
})
You can also chain multiple onTaskStarted
and onTaskFinished
handling (in case you want to separate some functionality):
import { PromisePool } from '@supercharge/promise-pool'
await PromisePool
.for(users)
.onTaskStarted(() => {})
.onTaskStarted(() => {})
.onTaskFinished(() => {})
.onTaskFinished(() => {})
.process(async (user, index, pool) => {
// processes the `user` data
})
Sometimes it’s useful to configure a timeout in which a task must finish processing. A task that times out is marked as failed. You may use the withTaskTimeout(<milliseconds>)
method to configure a task’s timeout:
import { PromisePool } from '@supercharge/promise-pool'
await PromisePool
.for(users)
.withTaskTimeout(2000) // milliseconds
.process(async (user, index, pool) => {
// processes the `user` data
})
Notice: a configured timeout is configured for each task, not for the whole pool. The example configures a 2-second timeout for each task in the pool.
Sometimes you want the processed results to align with your source items. The resulting items should have the same position in the results
array as their related source items. Use the useCorrespondingResults
method to apply this behavior:
import { setTimeout } from 'node:timers/promises'
import { PromisePool } from '@supercharge/promise-pool'
const { results } = await PromisePool
.for([1, 2, 3])
.withConcurrency(5)
.useCorrespondingResults()
.process(async (number, index) => {
const value = number * 2
return await setTimeout(10 - index, value)
})
/**
* source array: [1, 2, 3]
* result array: [2, 4 ,6]
* --> result values match the position of their source items
*/
For example, you may have three items you want to process. Using corresponding results ensures that the processed result for the first item from the source array is located at the first position in the result array (=index 0
). The result for the second item from the source array is placed at the second position in the result array, and so on …
The results
array returned by the promise pool after processing has a mixed return type. Each returned item is one of this type:
Symbol('notRun')
: for tasks that didn’t runSymbol('failed')
: for tasks that failed processingThe PromisePool
exposes both symbols and you may access them using
Symbol('notRun')
: exposed as PromisePool.notRun
Symbol('failed')
: exposed as PromisePool.failed
You may repeat processing for all tasks that didn’t run or failed:
import { PromisePool } from '@supercharge/promise-pool'
const { results, errors } = await PromisePool
.for([1, 2, 3])
.withConcurrency(5)
.useCorrespondingResults()
.process(async (number) => {
// …
})
const itemsNotRun = results.filter(result => {
return result === PromisePool.notRun
})
const failedItems = results.filter(result => {
return result === PromisePool.failed
})
When using corresponding results, you need to go through the errors
array yourself. The default error handling (collect errors) stays the same and you can follow the described error handling section above.
git checkout -b my-feature
git commit -am 'Add some feature'
git push origin my-new-feature
MIT © Supercharge
superchargejs.com · GitHub @supercharge · Twitter @superchargejs
FAQs
Map-like, concurrent promise processing for Node.js
The npm package @supercharge/promise-pool receives a total of 311,327 weekly downloads. As such, @supercharge/promise-pool popularity was classified as popular.
We found that @supercharge/promise-pool demonstrated a healthy version release cadence and project activity because the last version was released less than a year ago. It has 3 open source maintainers collaborating on the project.
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