# Yahoo! UI Library

### io 3.0.0

Yahoo! UI Library > io > io-queue.js (source view)
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       /**
        * Extends the IO base class to implement Queue for synchronous
        * transaction processing.
    	* @module io
    	* @submodule io-queue
    	*/

       /**
    	* @description Array of transactions queued for processing
    	*
    	* @property _yQ
    	* @private
    	* @static
    	* @type Object
    	*/
    	var _q = new Y.Queue(),

       /**
    	* @description Reference to "io:complete" event handler.
    	*
    	* @property _e
    	* @private
    	* @static
    	* @type Object
    	*/
    	_e,

    	_activeId,
       /**
    	* @description Property to determine whether the queue is set to
    	* 1 (active) or 0 (inactive).  When inactive, transactions
    	* will be stored in the queue until the queue is set to active.
    	*
    	* @property _qState
    	* @private
    	* @static
    	* @type int
    	*/
    	_qState = 1;

       /**
    	* @description Method for requesting a transaction, and queueing the
    	* request before it is sent to the resource.
    	*
    	* @method _queue
    	* @private
    	* @static
    	* @return Object
    	*/
    	function _queue(uri, c) {
    		var o = { uri: uri, id: Y.io._id(), cfg:c };

    		_q.add(o);
    		if (_qState === 1) {
    			_shift();
    		}

    		Y.log('Object queued.  Transaction id is' + o.id, 'info', 'io');
    		return o;
    	}

       /**
    	* @description Method Process the first transaction from the
    	* queue in FIFO order.
    	*
    	* @method _shift
    	* @private
    	* @static
    	* @return void
    	*/
    	function _shift() {
    		var o = _q.next();

    		_activeId = o.id;
    		_qState = 0;
    		Y.io(o.uri, o.cfg, o.id);
    	}

       /**
    	* @description Method for promoting a transaction to the top of the queue.
    	*
    	* @method _unshift
    	* @private
    	* @static
    	* @return void
    	*/
    	function _unshift(o) {
    		_q.promote(o);
    	}

    	function _next(id) {
    		_qState = 1;
    		if (_activeId === id && _q.size() > 0) {
    			_shift();
    		}
    	}

       /**
    	* @description Method for removing a specific, pending transaction from
    	* the queue.
    	*
    	* @method _remove
    	* @private
    	* @static
    	* @return void
    	*/
    	function _remove(o) {
    		_q.remove(o);
    	}

    	function _start() {
    		_qState = 1;

    		if (_q.size() > 0) {
    			_shift();
    		}
    		Y.log('Queue started.', 'info', 'io');
    	}

       /**
    	* @description Method for setting queue processing to inactive.
    	* Transaction requests to YUI.io.queue() will be stored in the queue, but
    	* not processed until the queue is reset to "active".
    	*
    	* @method _stop
    	* @private
    	* @static
    	* @return void
    	*/
    	function _stop() {
    		_qState = 0;
    		Y.log('Queue stopped.', 'info', 'io');
    	};

       /**
    	* @description Method to query the current size of the queue.
    	*
    	* @method _size
    	* @private
    	* @static
    	* @return int
    	*/
    	function _size() {
    		return _q.size();
    	};

    	_e = Y.on('io:complete', function(id) { _next(id); }, Y.io);

       /**
    	* @description Method to query the current size of the queue, or to
    	* set a maximum queue size.  This is the interface for _size().
    	*
    	* @method size
    	* @public
    	* @static
    	* @param {number} i - Specified maximum size of queue.
        * @return number
    	*/
    	_queue.size = _size;

       /**
    	* @description Method for setting the queue to active. If there are
    	* transactions pending in the queue, they will be processed from the
    	* queue in FIFO order. This is the interface for _start().
    	*
    	* @method start
    	* @public
    	* @static
        * @return void
    	*/
    	_queue.start = _start;

       /**
    	* @description Method for setting queue processing to inactive.
    	* Transaction requests to YUI.io.queue() will be stored in the queue, but
    	* not processed until the queue is restarted. This is the
    	* interface for _stop().
    	*
    	* @method stop
    	* @public
    	* @static
        * @return void
    	*/
    	_queue.stop = _stop;

       /**
    	* @description Method for promoting a transaction to the top of the queue.
    	* This is the interface for _unshift().
    	*
    	* @method promote
    	* @public
    	* @static
    	* @param {Object} o - Reference to queued transaction.
        * @return void
    	*/
    	_queue.promote = _unshift;

       /**
    	* @description Method for removing a specific, pending transaction from
    	* the queue. This is the interface for _remove().
    	*
    	* @method remove
    	* @public
    	* @static
    	* @param {Object} o - Reference to queued transaction.
        * @return void
    	*/
    	_queue.remove = _remove;

        Y.mix(Y.io, {
    		queue: _queue
        }, true);

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