tarn

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 Tarn = require('tarn').Tarn;

const pool = new Tarn({

  // 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
});

pool.acquire().promise.then(someResource => {
  return useResource(someResource);
}).then(someResource => {
  pool.release(someResource);
});

// 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()