tarn

What is tarn?

The tarn.js package is a small, robust resource pool for JavaScript. It is primarily used for managing a pool of resources such as database connections, ensuring efficient resource utilization and scalability in applications. It provides features like acquiring and releasing resources, timeout handling, and error management.

What are tarn's main functionalities?

Resource Pool Management

This code demonstrates how to create a resource pool with minimum and maximum limits, and manage resource acquisition and release. It handles timeouts and resource reaping intervals.

const { Pool } = require('tarn');
const pool = new Pool({
  create: () => Promise.resolve(new Resource()),
  destroy: resource => Promise.resolve(resource.dispose()),
  min: 2,
  max: 10,
  acquireTimeoutMillis: 30000,
  idleTimeoutMillis: 30000,
  reapIntervalMillis: 1000
});

pool.acquire().promise.then(resource => {
  console.log('Resource acquired');
  pool.release(resource);
});

Other packages similar to tarn

generic-pool

generic-pool is a robust resource pooling library similar to tarn. It supports priority queuing and more extensive configuration options for resource management. While tarn focuses on simplicity and specific use cases, generic-pool offers broader flexibility and customization.

pool2

pool2 is another resource pooling library that provides features like deferred resource creation and better error handling. It is designed to be a more modern and feature-rich alternative to older pooling libraries, offering a different API but similar core functionalities as tarn.

README

Why yet another resource pool?

Tarn is focused on robustness and ability to recover from errors. Tarn has timeouts for all operations that can fail or timeout so that you should never end up with pool full of crap. Tarn has a comprehensive test suite and we are committed to adding tests and fixing all bugs that are found.

Tarn will always remain simple.

Install

npm install tarn

Usage

const { Pool, TimeoutError } = require('tarn');

const pool = new Pool({

  // function that creates a resource. You can either pass the resource
  // to the callback or return a promise that resolves the resource
  // (but not both).
  create: (cb) => {
    cb(null, new SomeResource());
  },

  // validates a connection before it is used. Return true or false
  // from it. If false is returned, the resource is destroyed and a
  // another one is acquired.
  validate: (resource) {
    return true;
  },

  // function that destroys a resource. This is always synchronous
  // as nothing waits for the return value.
  destroy: (someResource) => {
    someResource.cleanup();
  },

  // minimum size
  min: 2,

  // maximum size
  max: 10,

  // acquire promises are rejected after this many milliseconds
  // if a resource cannot be acquired
  acquireTimeoutMillis: 30000,

  // create operations are cancelled after this many milliseconds
  // if a resource cannot be acquired
  createTimeoutMillis: 30000,

  // free resouces are destroyed after this many milliseconds
  idleTimeoutMillis: 30000,

  // how often to check for idle resources to destroy
  reapIntervalMillis: 1000,

  // long long to idle after failed create before trying again
  createRetryIntervalMillis: 200,

  // If true, when a create fails, the first pending acquire is
  // rejected with the error. If this is false (the default) then
  // create is retried until acquireTimeoutMillis milliseconds has
  // passed.
  propagateCreateError: false
});

// acquires a resource. The promise is rejected with `tarn.TimeoutError`
// after `acquireTimeoutMillis` if a resource could not be acquired.
const acquire = pool.acquire();

// acquire can be aborted using the abort method
acquire.abort();

// the acquire object has a promise property that gets reolved with
// the acquired resource
try {
  const resource = await acquire.promise;
} catch (err) {
  // if the acquire times out an error of class TimeoutError is thrown
  if (err instanceof TimeoutError) {
    console.log('timeout');
  }
}

// releases the resource.
pool.release(resource);

// returns the number of non-free resources
pool.numUsed()

// returns the number of free resources
pool.numFree()

// how many acquires are waiting for a resource to be released
pool.numPendingAcquires()

// how many asynchronous create calls are running
pool.numPendingCreates()

// waits for all resources to be returned to the pool and destroys them.
// pool cannot be used after this.
await pool.destroy();