pooling

Overview

pooling is a small general purpose resource pooling library. It is heavily inspired from James Cooper's excellent generic-pool library. This library was written after using that library for some time and desiring extra functionality (namely watching events and health checking).

Usage

var EventEmitter = require('events').EventEmitter;
var pooling = require('pooling');

var pool = pooling.createPool({
        checkInterval: 30000, // 30s (default is 30s)
        max: 10,              // Default is 1
        maxIdleTime: 120000,  // 2m (default is 1 hour)
        name: 'my pool',

        // Health check. Call the callback with an Error if you want
        // to indicate this client should die. destroy will still be
        // called (i.e., don't "double free").
        //
        // This function is called when an object is unused for
        // >= maxIdleTime.  If you don't provide a check function,
        // the default behavior is to mark the client for death.
        check: function check(client, callback) {
                if ((client.id % 2) !== 0)
                            return callback(new Error());

                return callback(null);
        },

        // callback is of the form function (err, client).
        create: function create(callback) {
                var client = new EventEmitter();
                client.id = Math.floor(Math.random() * 1000);
                return callback(null, client);
        },

        // destroy is for you to do cleanup with; the pool will have already
        // discarded the object (hence no callback)
        destroy: function destroy(client) {
                client.was = client.id;
                client.id = -1;
        }
    });

    pool.on('create', function (client) {
            console.log('client %d created', client.id);
    });

    pool.on('death', function (client) {
            console.log('client %d was killed', client.was);
    });

    pool.on('drain', function () {
            console.log('pool has no backlog or outstanding clients');
    });

    pool.acquire(function (err, client) {
            if (err) {
                    console.error('Unable to acquire: %s', err.stack);
                    process.exit(1);
            }

            pool.release(client);
            client.emit('error', new Error('die now'));
    });

    // Gracefully block future acquire calls and wait for clients to be
    // released
    pool.shutdown(function () {
            console.log('done');
            process.exit(0);
    });

By default the pool will remove clients on close, end, error and timeout events. You can override this by passing in an events array at pool creation time. You can also pass in a Bunyan Logger - pooling logs everything at the trace level.

Install

    npm install pooling

Development

To run unit tests and lint/style checks, just run:

    make prepush

You can generate coverage data by running:

    make cover

And opening ./cover_data/index.html.

License

The MIT License (MIT) Copyright (c) 2012 Mark Cavage

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.