mysql-queue-pool/lib/pool.js

Database connection pooling and query queueing.

/**
 * Connection pool.
 *
 * @file   utils/pool.js
 * @author Radek Pycka
 *
 * @todo implement timeouts
 */

var _ = require('underscore')._;

/**
 * @private
 * @param {Object} config
 */
function ConnectionPool(config) {
  this.constructor = config.constructor;
  this.maxSize = config.maxSize;

  this.cptr = 0;
  this.pool = [];
  this.queue = [];
  this.timeout = config.timeout;
}

/**
 * Acquire connection from the pool in round-robin fashion.
 *
 * @param {Function} callback
 */
ConnectionPool.prototype.acquire = function (callback) {
  var pool = this.pool;
  var cptr = this.cptr;
  var size = pool.length;
  var i = cptr;
  var item;

  if (size) {
    do {
      i = ++i % size;
      item = pool[i];

      if (!item.locked) {
        item.lock();
        _.defer(callback, null, item.object);
        this.cptr = i;

        return;
      }
    }
    while(i !== cptr);
  }

  // Nothing found, establish new connection or join waiting.
  if (size < this.maxSize) {
    var me = this;
    var object = this.constructor(function (err) {
      if (err) {
        me.release(object, true);
        console.log('DBM ' + err);
      }

      _.defer(callback, err, object);
    });

    pool.push(new Item(object));
  }
  else {
    this.queue.push(callback);
  }
};

/**
 * Return acquired object to the pool.
 *
 * @public
 * @idempotent
 *
 * @param {Object}  object
 * @param {Boolean} remove
 *   Whether to remove permanently object from the pool.
 */
ConnectionPool.prototype.release = function (object, remove) {
  for (var i = 0, max = this.pool.length ; i < max ; ++i) {
    var item = this.pool[i];

    if (item.object === object) {
      if (remove) {
        this.pool.splice(i, 1);
      }
      else if (this.queue.length) { // someone is waiting for connection
        _.defer(this.queue.shift, null, object);
      }
      else {
        item.unlock();
      }

      break;
    }
  }
};


/**
 * Wrapper around held object.
 *
 * @param {Object} object
 */
function Item (object) {
  this.object = object;
  this.locked = true;
}

/**
 * @public
 */
Item.prototype.lock = function () {
  this.locked = true;
};

/**
 * @public
 */
Item.prototype.unlock = function () {
  this.locked = false;
};


// Export public API.
exports.ConnectionPool = ConnectionPool;