p-limit vs async-mutex vs async-lock vs async-sema vs semaphore-async-await
Concurrency Control in JavaScript Comparison
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What's Concurrency Control in JavaScript?

Concurrency control libraries in JavaScript help manage access to shared resources in asynchronous code, preventing race conditions and ensuring that only a limited number of tasks can access a resource at a time. These libraries provide mechanisms like locks, semaphores, and limits to control how and when asynchronous functions can execute, making them essential for building reliable and efficient applications that handle concurrent operations. They are particularly useful in scenarios like API rate limiting, managing access to shared data, or coordinating tasks in a multi-threaded environment. Each library offers different approaches and features for managing concurrency, allowing developers to choose the one that best fits their needs.

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p-limit173,032,5652,42010.3 kB97 months agoMIT
async-mutex3,680,1821,29963 kB14a year agoMIT
async-lock2,722,19841918.3 kB52 years agoMIT
async-sema2,461,250646-94 years agoMIT
semaphore-async-await98,237101-28 years agoMIT
Feature Comparison: p-limit vs async-mutex vs async-lock vs async-sema vs semaphore-async-await

Locking Mechanism

  • p-limit:

    p-limit does not provide a traditional locking mechanism but instead limits the number of concurrent promises that can be executed at a time. You specify a concurrency limit, and the library ensures that only that many promises are running simultaneously, queuing the rest until a slot becomes available. This helps manage resource usage and prevent overwhelming external services.

  • async-mutex:

    async-mutex implements a mutex (mutual exclusion) locking mechanism that allows you to control access to a shared resource. It supports both exclusive locks (only one task can hold the lock at a time) and reentrant locks (a task can acquire the lock multiple times if it already holds it). This flexibility makes it suitable for various concurrency control scenarios.

  • async-lock:

    async-lock provides a simple locking mechanism that allows you to create locks around specific functions or code blocks. It ensures that only one task can execute the locked section at a time, preventing race conditions and ensuring data integrity. The locking is done using a key-based system, allowing you to create multiple locks with different keys if needed.

  • async-sema:

    async-sema implements a semaphore that allows a specified number of tasks to access a resource concurrently. You can set the maximum number of concurrent tasks, and the semaphore will manage access accordingly. This is useful for limiting resource usage and preventing overloading a service or system.

  • semaphore-async-await:

    semaphore-async-await provides a semaphore implementation that allows you to limit the number of concurrent tasks accessing a resource. It supports both async and sync functions, making it versatile for different use cases. The semaphore can be configured with a maximum concurrency level, and it queues tasks when the limit is reached, ensuring orderly execution.

Concurrency Control

  • p-limit:

    p-limit offers concurrency control at the promise level. You define a limit on the number of concurrent promises, and the library ensures that only that many promises are executed at a time. This is particularly useful for controlling resource usage in scenarios where you have a large number of asynchronous tasks that can be executed in parallel but need to be limited to avoid overwhelming the system.

  • async-mutex:

    async-mutex allows for fine-grained concurrency control with its mutex and reentrant lock features. You can control access to shared resources at a granular level, allowing for more flexible and efficient concurrency management. The reentrant lock feature allows the same task to acquire the lock multiple times, reducing the risk of deadlocks in certain scenarios.

  • async-lock:

    async-lock provides fine-grained control over concurrency by allowing you to lock specific sections of code. You can create locks with different keys, enabling multiple independent locks within the same application. This allows for concurrent execution of unlocked code while ensuring that locked sections are executed sequentially.

  • async-sema:

    async-sema provides coarse-grained concurrency control by limiting the number of concurrent tasks accessing a resource. You set a maximum concurrency level, and the semaphore enforces this limit, allowing only a specified number of tasks to execute simultaneously. This is useful for managing resource usage and preventing contention in high-concurrency environments.

  • semaphore-async-await:

    semaphore-async-await provides effective concurrency control by limiting the number of concurrent tasks accessing a resource. You can configure the maximum concurrency level, and the semaphore will manage access accordingly. It supports both async and sync functions, making it versatile for different use cases. The semaphore queues tasks when the limit is reached, ensuring that they are executed in the order they were acquired.

Ease of Use: Code Examples

  • p-limit:

    p-limit is easy to use and integrates seamlessly with promise-based functions. The API is simple, and the library provides clear documentation, making it easy to understand how to implement concurrency limits in your code. Example:

    const pLimit = require('p-limit');
const limit = pLimit(2); // Limit to 2 concurrent tasks

const tasks = Array.from({ length: 5 }, (_, i) =>
  limit(() => new Promise((resolve) => {
    setTimeout(() => {
      console.log(`Task ${i + 1} completed`);
      resolve();
    }, 1000);
  }))
);

await Promise.all(tasks);
  • async-mutex:

    async-mutex provides a simple and intuitive API for managing locks and mutexes. The documentation is clear, and the library is lightweight, making it easy to integrate into your projects. Example:

    const { Mutex } = require('async-mutex');
const mutex = new Mutex();

let counter = 0;

async function increment() {
  const release = await mutex.acquire();
  counter++;
  release(); // Release the lock
}

(async () => {
  await Promise.all([increment(), increment(), increment()]);
  console.log(counter); // Output: 3
});
  • async-lock:

    async-lock is easy to use and integrates well with existing asynchronous code. You can create locks with minimal setup and use them to wrap critical sections of your code. The API is straightforward, making it simple to implement locking without a steep learning curve. Example:

    const AsyncLock = require('async-lock');
const lock = new AsyncLock();

let sharedResource = 0;

function updateResource() {
  return lock.acquire('resource', async () => {
    const temp = sharedResource;
    await new Promise((resolve) => setTimeout(resolve, 100)); // Simulate async work
    sharedResource = temp + 1;
  });
}

(async () => {
  await Promise.all([updateResource(), updateResource(), updateResource()]);
  console.log(sharedResource); // Output: 3
});
  • async-sema:

    async-sema has a simple and straightforward API for creating and managing semaphores. It is easy to understand and use, making it a good choice for developers who need to implement concurrency limits quickly. Example:

    const { Sema } = require('async-sema');
const sema = new Sema(2); // Allow 2 concurrent tasks

async function limitedTask(id) {
  await sema.acquire(); // Acquire a semaphore
  console.log(`Task ${id} is running`);
  await new Promise((resolve) => setTimeout(resolve, 1000)); // Simulate async work
  sema.release(); // Release the semaphore
}

(async () => {
  await Promise.all([limitedTask(1), limitedTask(2), limitedTask(3), limitedTask(4)]);
});
  • semaphore-async-await:

    semaphore-async-await provides a simple and intuitive API for managing semaphores. It is easy to use and understand, making it a good choice for developers who need to implement concurrency limits quickly. Example:

    const { Semaphore } = require('semaphore-async-await');
const semaphore = new Semaphore(2); // Allow 2 concurrent tasks

async function limitedTask(id) {
  await semaphore.acquire(); // Acquire a semaphore
  console.log(`Task ${id} is running`);
  await new Promise((resolve) => setTimeout(resolve, 1000)); // Simulate async work
  semaphore.release(); // Release the semaphore
}

(async () => {
  await Promise.all([limitedTask(1), limitedTask(2), limitedTask(3), limitedTask(4)]);
});
How to Choose: p-limit vs async-mutex vs async-lock vs async-sema vs semaphore-async-await
  • p-limit:

    Choose p-limit if you want to limit the number of concurrent promises in a specific operation. It allows you to create a promise-based function that enforces a maximum concurrency level, making it useful for controlling resource usage in tasks like file uploads, API requests, or any operation that can benefit from concurrency control. This package is particularly helpful when working with asynchronous functions that can be executed in parallel, but you want to prevent overwhelming the system or external services.

  • async-mutex:

    Select async-mutex if you require a lightweight and flexible mutex implementation for your asynchronous code. It provides both exclusive locks and reentrant locks, allowing you to control access to shared resources with fine-grained control. This package is ideal for scenarios where you need to manage access to a resource while allowing the same task to acquire the lock multiple times if needed.

  • async-lock:

    Choose async-lock if you need a simple and effective locking mechanism for critical sections in your asynchronous code. It allows you to create locks around specific functions or code blocks, ensuring that only one task can execute them at a time. This is useful for preventing race conditions when multiple asynchronous operations might try to access or modify the same resource simultaneously.

  • async-sema:

    Use async-sema when you need a simple semaphore implementation to limit the number of concurrent tasks accessing a resource. It allows you to specify a maximum number of concurrent executions, making it perfect for scenarios like limiting API calls, controlling access to a shared resource, or managing concurrency in a task queue. This package is lightweight and easy to use, providing a straightforward API for managing concurrency limits.

  • semaphore-async-await:

    Select semaphore-async-await if you need a robust semaphore implementation that works seamlessly with async/await syntax. It provides a simple way to limit the number of concurrent tasks accessing a resource, with support for both async and sync functions. This package is ideal for scenarios where you want to enforce a concurrency limit while maintaining clean and readable code with async/await. It also supports queuing tasks when the limit is reached, ensuring that all tasks are executed in order.

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-mutex

async-mutex is a JavaScript library that provides a simple and efficient way to manage asynchronous locks in your code. It allows developers to create mutexes (mutual exclusions) that can help prevent race conditions when accessing shared resources in asynchronous environments. This is particularly useful in scenarios where multiple asynchronous operations might attempt to modify the same resource simultaneously. By using async-mutex, you can ensure that only one operation can access the resource at a time, leading to more predictable and reliable code.

While async-mutex is a great choice for managing asynchronous locks, there are other libraries that offer similar functionality. Here are a couple of alternatives:

  • async-lock is a lightweight library that provides a simple API for creating locks in asynchronous JavaScript code. It allows you to create named locks, which can be acquired and released in a straightforward manner. async-lock is particularly useful when you need to ensure that certain sections of your code are executed in a controlled manner, preventing overlapping execution of asynchronous tasks. Its simplicity and ease of use make it a popular choice for developers looking to manage concurrency in their applications.
  • mutexify is another library that provides a mutex implementation for JavaScript. It allows you to create mutexes that can be used to control access to shared resources in an asynchronous context. mutexify is designed to be lightweight and easy to integrate into existing codebases. It provides a simple API for acquiring and releasing locks, making it a good option for developers who need a straightforward solution for managing concurrency in their applications.

To explore how async-mutex compares with async-lock and mutexify, check out the comparison: Comparing async-lock vs async-mutex vs mutexify.

Similar Npm Packages to async-lock

async-lock is a JavaScript library designed to provide a simple and effective way to manage asynchronous locks. It is particularly useful in scenarios where you need to ensure that certain operations do not execute concurrently, which can help prevent race conditions and ensure data integrity. By using async-lock, developers can create critical sections in their code, allowing only one operation to proceed at a time while others wait for their turn. This is especially beneficial in environments where multiple asynchronous tasks may attempt to access shared resources.

While async-lock is a great solution for managing asynchronous operations, there are alternatives available that can also help with similar use cases. One notable alternative is:

  • async-mutex. This library provides a simple and lightweight way to create mutexes (mutual exclusions) for asynchronous operations. It allows developers to create locks that can be used to ensure that only one asynchronous operation runs at a time. The API is straightforward and easy to use, making it a suitable choice for those who need a simple locking mechanism without the additional features that async-lock may provide. If your application requires basic locking functionality, async-mutex can be an effective and minimalistic solution.

To see how async-lock compares with async-mutex, check out the comparison: Comparing async-lock vs async-mutex.

Similar Npm Packages to async-sema

async-sema is a lightweight semaphore implementation for managing asynchronous operations in JavaScript. It allows developers to control the concurrency of asynchronous tasks, ensuring that a specified number of tasks can run simultaneously. This can be particularly useful in scenarios where you want to limit the number of concurrent requests to an API or manage resource-intensive operations without overwhelming the system. The simplicity and efficiency of async-sema make it a great choice for developers looking to implement concurrency control in their applications.

However, there are several alternatives in the JavaScript ecosystem that provide similar functionality for managing asynchronous operations. Here are a few noteworthy options:

  • async-lock is a library that provides a simple way to create locks for asynchronous functions. It allows developers to ensure that only one instance of a function can run at a time, preventing race conditions and ensuring data integrity. async-lock is particularly useful when you need to protect shared resources or critical sections of code from concurrent access.

  • async-mutex is another library that offers mutex (mutual exclusion) functionality for asynchronous operations. It provides a straightforward API for creating locks that can be acquired and released, allowing developers to manage access to shared resources effectively. async-mutex is ideal for scenarios where you need to ensure that only one asynchronous operation can access a resource at a time.

  • p-limit is a utility that limits the number of concurrent promises. It allows you to run a specified number of promises in parallel, making it a great choice for managing concurrency in scenarios where you want to control the number of simultaneous asynchronous operations. p-limit is lightweight and easy to use, making it suitable for various use cases.

  • semaphore-async-await is a semaphore implementation that works seamlessly with async/await syntax. It allows developers to limit the number of concurrent asynchronous operations, similar to async-sema, but with a focus on providing a more intuitive API for those who prefer using async/await. This library is particularly useful for managing concurrency in modern JavaScript applications that leverage async/await for handling asynchronous code.

To see how async-sema compares with async-lock, async-mutex, p-limit, and semaphore-async-await, check out the comparison: Comparing async-lock vs async-mutex vs async-sema vs p-limit vs semaphore-async-await.

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.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-all - Run promise-returning & async functions concurrently with optional limited concurrency
  • More…
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