concurrent-promise-ts

An efficient promise executor'

This library allows to efficiently apply a potentially expensive function to all the elements of an iterable source.

// To dump the results of the operation into an array, use `all`
import {all} from 'concurrent-promise-ts'
 
function delay(ms: number): Promise<void> { } // pauses for `ms` millis.
 
// An iterable source.
const source = [1, 2, 3, 4, 5, 6, ... 1000];
 
// An expensive function
async function expensiveFunction(n: number): Promise<number> {
  await delay(1000);
  return n;
}
 
// Maximum number of `expensiveFunction` that will be running at a time.
const concurrency = 32; // defaults to 32
 
// results is of type Array<number>
const results = await all(source, expensiveFunction, concurrency); 

all returns a promise. It will be rejected if any error occurs while retrieving data from the source, or while executing the function.

For advanced functionality, execute returns an asynchronous generator that traverses the source according to the concurrency and backpressure settings.

import {execute} from 'concurrent-promise-ts'
 
function delay(ms: number): Promise<void> { } // pauses for `ms` millis.
 
// An asynchronous iterable source.
async function* source() {
  for (const number of [1, 2, 3, 4, 5, 6, ... 1000]) {
    await delay(50);
    yield number;
  }
}
 
// An expensive function
async function expensiveFunction(n: number): Promise<number> {
  await delay(1000);
  return n;
}
 
// Maximum number of `expensiveFunction` that will be running at a time.
const concurrency = 32; // defaults to 32
 
// If `false`, as `expensiveFunction` finishes for the first `concurrency` values of
// the source generator, the results are stored in a buffer and more values are
// requested. Repeats until the source generator finishes.
// If `true` the source generator won't be traversed if the one returned by
// `execute` isn't.
const backpressure = false; // defaults to false
 
// iterate
for await (const result of execute(source, expensiveFunction, concurrency, backpressure)) {
  console.log('finished for', result);
}