$ npm install generic-pool

1.0.9 - Dec 18 2011
   - Merged #25 (add getName() - contributed by BryanDonovan)
   - Merged #27 (remove sys import - contributed by botker)
   - Merged #26 (log levels - contributed by JoeZ99)

1.0.8 - Nov 16 2011
   - Merged #21 (add getter methods to see pool size, etc. - contributed by BryanDonovan)
   
1.0.7 - Oct 17 2011
   - Merged #19 (prevent release on the same obj twice - contributed by tkrynski)
   - Merged #20 (acquire() returns boolean indicating whether pool is full - contributed by tilgovi)

1.0.6 - May 23 2011
   - Merged #13 (support error variable in acquire callback - contributed by tmcw) 
      - Note: This change is backwards compatible.  But new code should use the two
              parameter callback format in pool.create() functions from now on.
   - Merged #15 (variable scope issue in dispense() - contributed by eevans)
   
1.0.5 - Apr 20 2011
   - Merged #12 (ability to drain pool - contributed by gdusbabek)
   
1.0.4 - Jan 25 2011
   - Fixed #6 (objects reaped with undefined timeouts)
   - Fixed #7 (objectTimeout issue)

1.0.3 - Dec 9 2010
   - Added priority queueing (thanks to sylvinus)
   - Contributions from Poetro
     - Name changes to match conventions described here: http://en.wikipedia.org/wiki/Object_pool_pattern
        - borrow() renamed to acquire()
        - returnToPool() renamed to release()
     - destroy() removed from public interface
     - added JsDoc comments
     - Priority queueing enhancements
   
1.0.2 - Nov 9 2010 
   - First NPM release

// Create a MySQL connection pool with
// a max of 10 connections and a 30 second max idle time
var poolModule = require('generic-pool');
var pool = poolModule.Pool({
    name     : 'mysql',
    create   : function(callback) {
        var Client = require('mysql').Client;
        var c = new Client();
        c.user     = 'scott';
        c.password = 'tiger';
        c.database = 'mydb';
        c.connect();
        
        // parameter order: err, resource
        // new in 1.0.6
        callback(null, c);
    },
    destroy  : function(client) { client.end(); },
    max      : 10,
    idleTimeoutMillis : 30000,
    log : true
});

// acquire connection - callback function is called
// once a resource becomes available
pool.acquire(function(err, client) {
    client.query("select * from foo", [], function() {
        // return object back to pool
        pool.release(client);
    });
});

Pool() accepts an object with these slots:

              name : name of pool (string, optional)
            create : function that returns a new resource
                       should call callback() with the created resource
           destroy : function that accepts a resource and destroys it
               max : maximum number of resources to create at any given time
 idleTimeoutMillis : max milliseconds a resource can go unused before it should be destroyed
                     (default 30000)
reapIntervalMillis : frequency to check for idle resources (default 1000),
     priorityRange : int between 1 and x - if set, borrowers can specify their
                     relative priority in the queue if no resources are available.
                     see example.  (default 1)
               log : true/false or function -
                       If a log is a function, it will be called with two parameters:
                                                - log string
                                                - log level ('verbose', 'info', 'warn', 'error')
                       Else if log is true, verbose log info will be sent to console.log()
                       Else internal log messages be ignored (this is the default)

 // create pool with priorityRange of 3
 // borrowers can specify a priority 0 to 2
 var pool = poolModule.Pool({
     name     : 'mysql',
     create   : function(callback) {
         // do something
     },
     destroy  : function(client) { 
         // cleanup.  omitted for this example
     },
     max      : 10,
     idleTimeoutMillis : 30000,
     priorityRange : 3
 });

 // acquire connection - no priority - will go at end of line
 pool.acquire(function(err, client) {
     pool.release(client);
 });

 // acquire connection - high priority - will go into front slot
 pool.acquire(function(err, client) {
     pool.release(client);
 }, 0);

 // acquire connection - medium priority - will go into middle slot
 pool.acquire(function(err, client) {
     pool.release(client);
 }, 1);

 // etc..

pool.drain(function() {
    pool.destroyAllNow();
});

// returns factory.name for this pool
pool.getName()

// returns number of resources in the pool regardless of
// whether they are free or in use
pool.getPoolSize()

// returns number of unused resources in the pool
pool.availableObjectsCount()

// returns number of callers waiting to acquire a resource
pool.waitingClientsCount()

$ npm install expresso
$ expresso -I lib test/*.js