p-limit vs async
JavaScript Concurrency Control Libraries Comparison
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What's JavaScript Concurrency Control Libraries?

Concurrency control libraries in JavaScript help manage asynchronous operations, allowing developers to execute multiple tasks simultaneously while controlling the flow and resource usage. These libraries provide utilities to handle tasks in parallel or limit the number of concurrent operations, which is crucial for optimizing performance and preventing resource exhaustion in applications that perform I/O operations or handle multiple requests.

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p-limit162,248,961
2,50711.7 kB57 days agoMIT
async67,943,133
28,222808 kB18a year agoMIT
Feature Comparison: p-limit vs async

Concurrency Control

  • p-limit:

    p-limit allows you to specify a maximum number of concurrent promises that can be executed at once. This is particularly useful for controlling resource usage and preventing overwhelming external services, such as APIs or databases, by limiting the number of simultaneous requests.

  • async:

    Async provides various methods for concurrency control, allowing developers to execute functions in series, parallel, or with a specific limit on concurrent executions. This flexibility makes it suitable for complex workflows where task dependencies and execution order are important.

Ease of Use

  • p-limit:

    p-limit has a simple and intuitive API that is easy to use. It requires minimal setup and is straightforward to integrate into existing codebases, making it accessible for developers who need quick concurrency control without additional complexity.

  • async:

    Async has a rich API with many utility functions, which may have a steeper learning curve for beginners. However, once familiar, developers can leverage its powerful features to handle complex asynchronous flows effectively.

Performance

  • p-limit:

    p-limit is designed to be lightweight and efficient, focusing solely on limiting concurrency. This makes it a better choice for performance-sensitive applications where the overhead of a larger library like Async is unnecessary.

  • async:

    While Async is powerful, its extensive feature set can introduce some overhead. For lightweight tasks, this might not be an issue, but for performance-critical applications, the overhead should be considered when choosing Async over simpler solutions.

Error Handling

  • p-limit:

    p-limit relies on standard promise error handling. While it does not provide additional error handling features, it allows developers to handle errors in a straightforward manner by using standard promise catch blocks.

  • async:

    Async provides built-in error handling mechanisms, allowing developers to manage errors in asynchronous flows effectively. It supports callbacks and promises, making it easier to catch and handle errors at various stages of execution.

Community and Ecosystem

  • p-limit:

    p-limit is a newer and more specialized library, which means its community is smaller compared to Async. However, it is gaining traction for its simplicity and effectiveness in specific use cases, and documentation is available for developers looking to implement it.

  • async:

    Async has a large community and a well-established ecosystem, with many resources available for learning and troubleshooting. Its popularity means that developers can find numerous examples and documentation to assist with implementation.

How to Choose: p-limit vs async
  • p-limit:

    Choose p-limit if your primary concern is to limit the number of concurrent promises being executed at any given time. It is lightweight and straightforward, making it suitable for scenarios where you need to control the concurrency of asynchronous operations without the overhead of a larger library. p-limit is perfect for managing API requests or file processing where too many concurrent operations could lead to performance degradation.

  • async:

    Choose Async if you need a comprehensive library that provides a wide range of utilities for working with asynchronous JavaScript. It is ideal for complex workflows that require various control flow patterns, such as series, parallel, and waterfall execution of tasks. Async is particularly useful for handling multiple asynchronous operations where the order of execution matters.

Similar Npm Packages to p-limit

p-limit is a utility library that allows developers to limit the number of concurrent promises that can be executed at a time. This is particularly useful when dealing with APIs or other asynchronous operations where you want to avoid overwhelming the server or hitting rate limits. By using p-limit, you can control the flow of asynchronous tasks, ensuring that only a specified number of them run concurrently, while the others wait in line until a slot becomes available.

While p-limit is a great tool for managing concurrency, there are other libraries that provide similar functionality. Here are a couple of alternatives:

  • p-queue is a promise queue that allows you to manage the concurrency of asynchronous tasks. It provides a more feature-rich solution than p-limit, with options for prioritizing tasks, setting a maximum concurrency level, and even handling retries. If you need more control over the order and execution of your asynchronous operations, p-queue is an excellent choice. It’s particularly useful for scenarios where you need to manage complex workflows or prioritize certain tasks over others.

  • p-throttle is another alternative that focuses on limiting the rate at which a function can be called. Unlike p-limit, which limits concurrent executions, p-throttle allows you to control how often a function can be invoked over time. This can be particularly useful for scenarios like API rate limiting, where you want to ensure that a function is not called too frequently. If your primary concern is controlling the rate of function execution rather than managing concurrency, p-throttle is the right tool for the job.

To see how p-limit compares with p-queue and p-throttle, check out the comparison: Comparing p-limit vs p-queue vs p-throttle.

Similar Npm Packages to async

async is a utility module that provides powerful functions for working with asynchronous JavaScript. It simplifies the process of managing asynchronous operations, allowing developers to write cleaner and more maintainable code. With features like parallel execution, series execution, and control flow, async is particularly useful for handling complex asynchronous workflows. However, there are several alternatives in the JavaScript ecosystem that also provide similar functionalities. Here are a few notable ones:

  • bluebird is a fully-featured promise library that offers a wide range of utilities for working with promises. It enhances the native Promise functionality by providing additional features such as cancellation, progress tracking, and more robust error handling. bluebird is known for its performance and is a great choice for developers looking for an advanced promise library that can handle complex asynchronous tasks with ease.

  • p-map is a lightweight utility that allows you to map over an array asynchronously, executing a provided function for each element in parallel. It is particularly useful when you need to perform asynchronous operations on an array of items and want to control the concurrency level. p-map is simple to use and can be a great alternative for scenarios where you need to process multiple asynchronous tasks without the overhead of a larger library.

  • q is another promise library that focuses on providing a simple and straightforward API for working with asynchronous code. It was one of the earlier promise libraries in the JavaScript ecosystem and offers features like chaining, error handling, and more. While it may not be as feature-rich as some of the newer libraries, q is still a solid choice for developers looking for a lightweight solution for managing asynchronous operations.

To see how async compares with bluebird, p-map, and q, check out the comparison: Comparing async vs bluebird vs p-map vs q.

README for p-limit

p-limit

Run multiple promise-returning & async functions with limited concurrency

Works in Node.js and browsers.

Install

npm install p-limit

Usage

import pLimit from 'p-limit';

const limit = pLimit(1);

const input = [
	limit(() => fetchSomething('foo')),
	limit(() => fetchSomething('bar')),
	limit(() => doSomething())
];

// Only one promise is run at once
const result = await Promise.all(input);
console.log(result);

API

pLimit(concurrency) default export

Returns a limit function.

concurrency

Type: number
Minimum: 1

Concurrency limit.

limit(fn, ...args)

Returns the promise returned by calling fn(...args).

fn

Type: Function

Promise-returning/async function.

args

Any arguments to pass through to fn.

Support for passing arguments on to the fn is provided in order to be able to avoid creating unnecessary closures. You probably don't need this optimization unless you're pushing a lot of functions.

limit.map(array, mapperFunction)

Process an array of inputs with limited concurrency.

The mapper function receives the item value and its index.

Returns a promise equivalent to Promise.all(array.map((item, index) => limit(mapperFunction, item, index))).

This is a convenience function for processing inputs that arrive in batches. For more complex use cases, see p-map.

limit.activeCount

The number of promises that are currently running.

limit.pendingCount

The number of promises that are waiting to run (i.e. their internal fn was not called yet).

limit.clearQueue()

Discard pending promises that are waiting to run.

This might be useful if you want to teardown the queue at the end of your program's lifecycle or discard any function calls referencing an intermediary state of your app.

Note: This does not cancel promises that are already running.

limit.concurrency

Get or set the concurrency limit.

limitFunction(fn, options) named export

Returns a function with limited concurrency.

The returned function manages its own concurrent executions, allowing you to call it multiple times without exceeding the specified concurrency limit.

Ideal for scenarios where you need to control the number of simultaneous executions of a single function, rather than managing concurrency across multiple functions.

import {limitFunction} from 'p-limit';

const limitedFunction = limitFunction(async () => {
	return doSomething();
}, {concurrency: 1});

const input = Array.from({length: 10}, limitedFunction);

// Only one promise is run at once.
await Promise.all(input);

fn

Type: Function

Promise-returning/async function.

options

Type: object

concurrency

Type: number
Minimum: 1

Concurrency limit.

FAQ

How is this different from the p-queue package?

This package is only about limiting the number of concurrent executions, while p-queue is a fully featured queue implementation with lots of different options, introspection, and ability to pause the queue.

Related

  • p-throttle - Throttle promise-returning & async functions
  • p-debounce - Debounce promise-returning & async functions
  • p-map - Run promise-returning & async functions concurrently with different inputs
  • p-all - Run promise-returning & async functions concurrently with optional limited concurrency
  • More…
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